veterinary parasitology- the practical veterinarian
DESCRIPTION
Veterinary parasitologyTRANSCRIPT
-
Copyright 2001 by ButterworthHeinemann
A member of the Reed Elsevier group
All rights reserved.
No part of this publication may be reproduced, stored in a retrieval system, ortransmitted in any form or by any means, electronic, mechanical, photocopying,recording, or otherwise, without the prior written permission of the publisher.
Every effort has been made to ensure that the drug dosage schedules within thistext are accurate and conform to standards accepted at time of publication.However, as treatment recommendations vary in the light of continuingresearch and clinical experience, the reader is advised to verify drug dosageschedules herein with information found on product information sheets. This isespecially true in cases of new or infrequently used drugs.
Recognizing the importance of preserving what has been written, ButterworthHeinemann prints its books on acid-free paper wheneverpossible.
ButterworthHeinemann supports the efforts of American Forestsand the Global ReLeaf program in its campaign for the betterment oftrees, forests, and our environment.
Library of Congress Cataloging-in-Publication DataBallweber, Lora Rickard, 1958
Veterinary parasitology / Lora Rickard Ballweber.p. ; cm. (Practical veterinarian)
Includes bibliographical references and index.ISBN 0-7506-7261-7 (alk. paper)
1. Veterinary parasitology. I. Title. II. Series.[DNLM: 1. Parasitic Diseases, AnimalHandbooks. SF 810.A3 B193v 2001]SF810.A3 B35 2001]636.089696dc21 00-063083
British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.
The publisher offers special discounts on bulk orders of this book.For information, please contact:
Manager of Special SalesButterworthHeinemann225 Wildwood AvenueWoburn, MA 01801-2041Tel: 781-904-2500Fax: 781-904-2620
For information on all ButterworthHeinemann publications available, contactour World Wide Web home page at: http://www.bh.com
10 9 8 7 6 5 4 3 2 1
Printed in the United States of America
-
Series Preface
The Practical Veterinarian series was developed to helpveterinary students, veterinarians, and veterinary techni-cians find answers to common questions quickly. Unlikelarger textbooks, which are filled with detailed informa-tion and meant to serve as reference books, all the booksin The Practical Veterinarian series are designed to cut tothe heart of the subject matter. Not meant to replace thereference texts, the guides in our series complement thelarger books by serving as an introduction to each topicfor those learning the subject matter for the first time oras a quick review for those who already have masteredthe basics of each subject.
The titles for the books in our series are selected toprovide information for the most common subjects onewould encounter in veterinary school and veterinarypractice. The authors are experienced and establishedclinicians who can present the subject matter in an easy-to-understand format. This helps both the first-time stu-dent of the subject and the seasoned practitioner toassess information often difficult to comprehend.
It is our hope that the books in The Practical Veteri-narian series will meet the needs of readers and serve asa constant source of practical and important informa-tion. We welcome comments and suggestions that will
vii
-
help us improve future editions of the books in thisseries.
Shawn P. Messonnier, D.V.M.
viii Series Preface
-
Preface
Unknowingly, I was first exposed to the discipline of vet-erinary parasitology as a youngster when my grandfa-ther, Roy V. Stambaugh, gave me his copy of a 1923USDA publication on the diseases of horses. In thumb-ing through it, I came upon an illustration of bots thatwere living in the stomach of the horse. While repulsed,I was at the same time fascinated that such a lifestyle wasoccurring with apparently little harm to the horse! Per-haps that is why, years later, I chose to accept an assist-antship to study for a Masters in parasitology ratherthan ruminant nutrition, and I have thoroughly enjoyedveterinary parasitology over essentially the past 20 years.As first a student and now a veterinary medical educator,I have seen numerous reference materials on this sub-ject. Many texts have become standards in the requiredbook list, but the most common complaint from veteri-nary students is they are not user-friendly and are tooverbose. Therefore, I was delighted to have the oppor-tunity to write a text that I hope is user-friendly. The out-line format was chosen because it is designed to presentinformation in a succinct, easy-to-read, and readilyaccessible format, thus, making this a quick referenceguide to the nuts and bolts of the parasites of veterinaryimportance designed for the veterinary medical student.
ix
-
When designing this book, I was confronted withthe same question we are all confronted with in ourcourses: what material to include. The first decision waswhether to limit it to the usual dogs, cats, horses, etc., orto include birds, reptiles, rodents, and other small mam-mals. Shear volume of material made the choice formeit would have to be limited to traditional domesti-cated animals (including poultry) with a few rodentsand small mammals included in the arthropod section.Next was which actual parasites to include. Decisionshere were governed by whether the parasite is common,has dire consequences if missed, or possesses someunique attribute or ability. Some parasites are encoun-tered so infrequently that inclusion in a quick referenceguide is not feasible. Others, such as Spirocerca lupi, areincluded because of a unique attribute; in this case, itsassociation with neoplasia. Still others, such as Acan-thocheilonema (=Dipetalonema) reconditum, are includedbecause of the difficulty in differentiating diagnosticstages from those of other, more pathogenic parasites;in this case, distinguishing microfilariae from those pro-duced by the heartworm, Dirofilaria immitis. Althoughsome parasites near and dear to me were not included,I believe that those essential to a veterinary medical education are.
The book begins with an introduction explainingsome basic concepts of parasitology and taxonomic clas-sification. Chapter 2 is devoted solely to ectoparasites.Chapter 3 is an introductory chapter to the endopara-
x Preface
-
sites, describing the characteristics and generalized lifecycles of each group (protozoans, nematodes, cestodes,digenetic trematodes, acanthocephalans). Host-parasitelists are provided here as well. The subsequent chaptersdescribe the parasites according to body organ system.Chapters 4 to 6 describe the parasites of the gastroin-testinal tract, Chapter 7 describes the cardiopulmonarysystem, and Chapter 8 covers the remaining organ sys-tems. Geographic distribution and relative significanceto both veterinary medicine and public health areincluded for each parasite as a guide to the student as tothe general importance of the parasite.
Information related to treatment of helminths hasbeen summarized in tables for approved compoundsavailable in the United States. Dosages and treatmentschedules should be verified on package inserts prior touse. In cases where approved drugs are not available,information on types and dosages of drugs used suc-cessfully is included within the text. However, thereader is reminded that this constitutes extra-label druguse and it is the responsibility of the attending veteri-narian to determine the dosage and best treatment forthe animal. Always be aware of contraindications; forexample, many collies and dogs of related herdingbreeds may suffer potentially fatal idiosyncratic reac-tions to ivermectin at doses as low as 100 mg/kg.
I would like to acknowledge Dr. Robert Bergstromwho offered me that assistantship in veterinary para-sitology those many years ago and fostered my fascina-
Preface xi
-
tion with this subject. I would also like to thank Dr. EricHoberg and past and present colleagues at MississippiState University, including Drs. Carla Siefker, AlanRathwell, Harry Jacobson, George Hurst, CarolynBoyle, Sharon Black, Terry Engelken, and Linda Pote,for their help and stimulating discussions over the pastfew years. Finally, I express sincere appreciation to myhusband for his patience and understanding when Ineeded to be working rather than fishing, and to therest of my family who do not know exactly what it is Ido, but have always supported my decision to do it.
L.R.B.
xii Preface
-
1Introduction
Symbiosis refers to any association, either temporary orpermanent, that exists between two organisms of differ-ent species. There are several types of symbiotic relation-ships, including predator-prey, phoresis, mutualism,commensalism, and parasitism. In the predator-prey rela-tionship, the association is one that is very short andresults in harm (i.e., death) to one member while bene-fiting the other. Phoresis refers to a relationship in whichone member of the association is mechanically carriedabout by the second member with no harm inflicted oneither. Mutualism refers to a relationship in which bothmembers of the association benefit as a result of the rela-tionship. Commensalism refers to a relationship in whichone member of the association benefits while the second
1
-
member receives neither benefit nor harm. Finally, para-sitism refers to a relationship in which one member ofthe associationthe parasitelives in or on the sec-ondthe host. The parasite derives nutritional benefitfrom the host and is usually considered harmful to thehost, although the degree of harm can vary greatly. It isthe parasites and parasitic diseases of domestic animalsthat we refer to as the discipline of veterinary parasitol-ogy, the subject of this book.
To understand parasites and the diseases they cause,one must first understand what a species is and the con-cepts of classification. Although not perfect, the mostwidely accepted definition of a species is an interbreedingpopulation that is reproductively isolated from other suchpopulations. For example, horses are host to manyspecies of small strongyles. As many as 1520 species ofthese parasites may be found living in the colon of thesame horse at the same time, yet they cannot interbreedand are, thus, separate species. We recognize the fact thatmany of these species are related, some more closely thanothers, by considering them to be in the same genus or inclosely related genera within the same family. These rela-tionships, then, are the basis of the Linnaean system ofclassification. There are millions of organisms on earth,each of which may have a different common name in dif-ferent regions of the world. Conversely, the same com-mon name may be used in different regions of the worldto refer to different species. In order to bring about sta-bility and universality, a system of classification has been
2 Introduction
-
devised in which all organisms are given a Latin binomial.This consists of a genus name (capitalized) followed bythe species name (lowercase). Both genus and speciesnames are italicized. Each species refers to a specificorganism and both genus and species names are givenwhen referring to that particular organism, for example,Dirofilaria immitis for the heartworm of dogs. Similarspecies are grouped within the same genus, similar gen-era within the same family, similar families within thesame order, similar orders within the same class, similarclasses within the same phylum, and similar phylagrouped together in the same kingdom. In order tocommunicate with colleagues, it is important to at leastlearn the species names of the parasites.
Identification is the process of determining to whichof these taxonomic groups an organism belongs. It is,generally, based on morphologic characteristics that areused to describe a certain species, genus, family, etc.Diagnosis, on the other hand, usually refers to the processof determining the cause of a disease. In this book, theterm diagnosis is used to refer to the process of deter-mining the presence of or how to identify a particularparasite species and not the determination of the causeof the clinical signs present. For example, diarrhea in ayoung calf may have a bacterial or viral cause and havelittle or nothing to do with the coccidial infection pres-ent. However, identification of oocysts in the feces maylead the uninitiated to misdiagnose coccidiosis. Alwaysrememberinfection does not equal disease.
Introduction 3
-
2Arthropods
Ectoparasites, most of which are arthropods, are thoseparasites that live on the body of the host. Some spendtheir entire life on the host, others spend only parts oftheir life on the host, while still others only occasionallyvisit the host. The ectoparasites most veterinarians dealwith directly are those that live all or much of their lifeon the host. Those that are periodic visitors to the hostare not usually on the animals when presented to thepractitioner. Although called upon to treat the effects ofthese periodic parasites, most veterinarians are notdirectly involved in their control. Consequently, thischapter focuses on those parasites spending all or muchof their life on the host with only brief mention of theperiodic parasites.
5
-
Classification of the ArthropodsKingdom: AnimaliaPhylum: ArthropodaClass: Arachnida (scorpions, spiders, mites, and
ticks)Order: Acarina (mites and ticks)Class: Insecta (insects)Order: Mallophaga (chewing or biting lice)
Anoplura (sucking lice)Siphonaptera (fleas)Diptera (two-winged flies)
Importance Intermediate hosts for various parasites.
Vectors for bacteria, viruses, and other pathogens.
Direct causal agents of disease.
Produce venoms that may be toxic.
Morphology Arachnids: body divided into two parts (cephalotho-
rax [fusion of head and thorax] and abdomen) orcompletely fused; adults with four pairs of legs;antennae absent; wingless.
6 Arthropods
-
Insects: body divided into three parts (head, thorax,abdomen); adults with three pairs of legs; antennaepresent; wings present or absent.
Ticks (Arachnida)Ticks are divided into two families: the Argasidae (softticks) and the Ixodidae (hard ticks). Table 21 outlinesthe important characteristics of each family.
Life Cycle
Simple metamorphosis with larval and nymphalstages resembling adults.
Separate sexes with females laying eggs off the host.
Larva (six legs, no reproductive organs) hatches,feeds on host and molts to nymph.
Nymph (eight legs, no functional reproductiveorgans) feeds on host and molts to another nymph(soft ticks) or adult (hard ticks).
Soft ticks have two or more nymphal stages; hardticks have only one.
All adult hard ticks feed on blood whereas not alladult soft ticks do.
Soft ticks tend to live inside (burrows, dens, hutches,etc.), feed rapidly, and spend relatively little time onthe host. Hard ticks tend to live outdoors, feedslowly, and spend longer time on the host.
Arthropods 7
-
8 Arthropods
Tab
le 2
1Im
port
ant C
hara
cter
istic
s of
Sof
t and
Har
d Ti
cks
Char
acte
rA
rgas
idae
(So
ft T
icks
)Ix
odid
ae (
Har
d T
icks
)
Scut
um
Abse
ntPr
esen
t
mal
es
cove
rs e
ntire
dor
sal
surfa
ce
fe
mal
es
cove
rs p
art o
f dor
sal
surfa
ce
Mou
thpa
rtsH
idde
n w
hen
view
ed fr
om th
e do
rsal
sur
face
Visi
ble
whe
n vi
ewed
from
the
dors
al s
urfa
ce
Feed
ing
Larv
ae fe
ed s
low
ly, o
ver s
ever
al
days
; nym
phs
and
adul
ts fe
ed
quic
kly,
sev
eral
tim
es
Larv
ae, n
ymph
s, a
nd a
dults
feed
on
ce, r
equi
ring
seve
ral d
ays
to
repl
etio
n Li
fe s
tage
sEg
g, la
rva,
two
or m
ore
nym
phs,
ad
ult
Egg,
larv
a, n
ymph
, adu
lt
-
Most ticks cannot tolerate direct sunlight, dryness,or excessive rainfall; tick activity decreases duringthe cold months and increases during spring, sum-mer, and fall.
Hard ticks can be classified as either one-host (allstages on one host), two-host (two stages on one host),or three-host (all stages on different hosts) ticks.
Common Soft Ticks in North America
ARGAS SPP. In the United States, distributed along the Gulf of
Mexico and the Mexican border.
Parasitize wild and domestic birds, occasionallyhumans.
Active primarily in evening hours.
Annoyance leads to decreased egg production;heavy infestations may cause anemia.
Development from egg to adult may take as little as30 days; may survive months (larvae, nymphs) ormore than 2 years (adults) without a blood meal.
OTOBIUS MEGNINI (SPINOSE EAR TICK) Generally distributed throughout North America.
Parasitize cattle, horses, other domestic animals, andhumans.
Arthropods 9
-
One-host tick in which larvae and nymphs feed inthe ear canal; unfed nymphs can survive as long as 2months.
Adults have vestigial mouthparts and do not feed;therefore, adult females lay a single clutch of eggs.
Common Hard Ticks in North America
RHIPICEPHALUS SANGUINEUS (BROWN DOG TICK) Three-host tick with all stages preferring dogs; can
feed on humans.
Originally found in the tropics; cannot overwinter incold, temperate regions but will survive indoors inthese areas; found in most of the United States andparts of southeast Canada.
Egg to egg development may be completed in as lit-tle as 2 months; unfed adults may survive for over ayear.
Transmit Babesia canis, Erlichia canis, possibly Hepato-zoon americanum.
AMBLYOMMA SPP. Two species are commonAmblyomma americanum
(lone star tick) and Amblyomma maculatum (Gulfcoast tick).
Both are three-host ticksadults prefer feeding onlarger animals (cattle and other livestock) and
10 Arthropods
-
other stages prefer feeding on foxes and similar-sized animals.
In the United States, A. maculatum is distributedalong Atlantic and Gulf coastal areas, whereas A.americanum is distributed in the southeastern region,into the Midwest and on the Atlantic coast.
Ambylomma americanum can produce severe anemiaand may transmit tularemia, Rocky Mountain spot-ted fever, and Lyme disease.
Amblyomma maculatum produces painful bite woundsthat swell and may become secondarily infected;implicated as a cause of tick paralysis; transmit Hepa-tozoon americanum.
DERMACENTOR SPP. Dermacentor variabilis (American dog tick)disjunct
populations occur across the United States, intoCanada, and Mexico.
Dermacentor andersoni (Rocky Mountain wood tick)widely distributed across western United States andCanada.
Both are three-host tickslarvae and nymphs preferfeeding on small rodents, adults prefer larger ani-mals (including dogs and humans).
Both can transmit Rocky Mountain spotted fever,tularemia, and can cause tick paralysis.
Arthropods 11
-
IXODES SPP. Several species or subspecies found across the
United States.
Three-host tick with larvae and nymphs preferringsmall rodents and adults preferring deer.
Transmits Lyme disease.
Other Important Genera
BOOPHILUS SPP. Two species of importance in North America
Boophilus microplus and Boophilus annulatus (Ameri-can cattle tick).
One-host ticks with B. annulatus preferring cattleand B. microplus preferring large animals in general(cattle, goats, deer, etc.).
Has been eradicated from the United States and,therefore, if encountered must be reported to stateand federal authorities.
Boophilus annulatus transmits Texas cattle fever (Babesiabigemina); both can transmit Anaplasma marginale.
HAEMAPHYSALIS SPP. Important parasite of wild mammals and birds;
rarely of dogs, cats, or humans.
Three-host ticks distributed from Alaska toArgentina.
12 Arthropods
-
Diagnosis
Ticks should be collected carefully in order to keep themouthparts intact. Preserving intact specimens in 70%ethanol or isopropyl alcohol is recommended, although5% formalin will do. The specific identification of tickscan be challenging, particularly if dealing with larval ornymphal forms. However, adults can be identified togenus using the shape of their capitulum and length oftheir mouthparts, the presence or absence of markings onthe scutum, and body structures. Table 22 presents keymorphologic characteristics that can be used to distin-guish the North American genera of hard ticks.
Treatment and Control
For dogs, dichlorvos, carbaryl, fipronil, and selamectincan be used. Fipronil on cats is highly effective. Flea andtick collars are available for dogs and cats. To control R.sanguineus indoors, spray building with Diazinon.Remove vegetation and debris from bed and yards todecrease tick survival. Spray or dust with acaricide to killthose that remain.
For lactating dairy cattle, coumaphos and dichlorvoscan be used. These and malathion may be used in non-lactating beef and dairy cattle. Coumaphos is effectivefor horses. Environmental modification for livestock isoften impractical.
Insecticidal dusts or emulsion concentrates are usedin the treatment of O. megnini infestations.
Arthropods 13
-
14 ArthropodsTa
ble
22
Key
Mor
phol
ogic
Cha
ract
eris
tics
Use
d to
Dis
tingu
ish
the
Nor
th A
mer
ican
G
ener
a of
Har
d Ti
cks
and
Boo
philu
s
Gen
us
An
al G
roov
e*
* Loc
atio
n of
gro
ove,
if p
rese
nt, i
n re
latio
n to
anu
s.
Bas
is C
apit
uli
or
Mou
thp
arts
Eyes
Scu
tal
Mar
kin
gsFe
stoo
ns
Ixod
esAn
terio
rM
outh
parts
long
Abse
ntIn
orna
te
Inor
nate
= n
o w
hite
mar
ks o
n th
e sc
utum
; orn
ate
= w
hite
mar
ks p
rese
nt o
n sc
utum
.
Abse
nt
Rhip
icep
halu
sPo
ster
ior
Hex
agon
al b
asis
ca
pitu
liPr
esen
tIn
orna
tePr
esen
t
Ambl
yom
ma
Post
erio
rM
outh
parts
muc
h lo
nger
than
ba
sis
capi
tuli
Pres
ent
Orn
ate
Pres
ent
Der
mac
ento
rAb
sent
Rect
angu
lar b
asis
ca
pitu
liPr
esen
tO
rnat
ePr
esen
t
Hae
ma-
phys
alis
Post
erio
rSe
cond
pal
pal s
eg-
men
t ar
ed la
t-er
ally
Abse
ntIn
orna
tePr
esen
t
Boo
philu
sAb
sent
Hex
agon
al b
asis
ca
pitu
li, s
hort
mou
thpa
rts
Pres
ent
Inor
nate
Abse
nt
-
Mites (Arachnida)Mites can be divided into two major groups: sarcopti-form and nonsarcoptiform mites. The sarcoptiformmites can be subdivided into those that burrow or tunnelwithin the epidermis and those that do not. Sarcopti-form mites are distinguished from nonsarcoptiformmites by possessing a round to oval-shaped body. Thelegs of sarcoptiform mites also have pedicels (stalks) atthe tips that may be long or short. If long, they may bejointed or unjointed. Suckers may be present at the tip ofthe stalk. These characteristics are very important foridentification. Although geographic distribution varieswith species of mite, in general, mites are found through-out the world.
Life Cycle
Simple metamorphosis with larval and nymphalstages resembling adults.
Separate sexes with females laying eggs on the host.
Larva (six legs) hatches, may or may not feed, andmolts to nymph.
Nymph (eight legs) feeds on host and molts toanother nymph (sarcoptiform mites living on sur-face) or adult (burrowing sarcoptiform mites; non-sarcoptiform mites).
Except for some mites of birds, mites tend to spendentire life on the host; for most mites, transmission
Arthropods 15
-
is primarily by direct contact although fomites canplay a role.
Sarcoptiform Mites
TUNNELING SARCOPTIFORM MITES Table 23 presentsthe host spectrum and characteristic lesions of the com-mon tunneling sarcoptiform mites.
SURFACE-DWELLING SARCOPTIFORM MITES Table 24presents the host spectrum and characteristic lesions of thecommon surface-dwelling sarcoptiform mites.
Non-Sarcoptiform Mites
DEMODEX SPP. These host-specific mites live in the hairfollicles and sebaceous glands of humans and mostdomestic animals. In most animals, these mites are con-sidered normal, nonpathogenic fauna of the skin. How-ever, particularly in the dog, serious disease can result.Transmission is by direct contact. The cigar-shaped bodymakes these mites easily recognizable.
Demodex canis Localized demodecosis: patchy alopecia, especially
of the muzzle, face, and bony projections on extrem-ities; nonpruritic; most recover spontaneously;recurrence is rare.
16 Arthropods
-
Arthropods 17
Tab
le 2
3H
ost,
Spec
ies,
Key
Cha
ract
eris
tics,
and
Les
ions
Cau
sed
by T
unne
ling
Sarc
optif
orm
Mite
s
Mit
eH
ost
Lesi
ons
Com
mon
Sit
esO
ther
Sarc
opte
s sc
abei
v.
cani
s
Dog
sIn
itial
ly
eryt
hem
a-to
us, t
hen
papu
lar;
beco
min
g cr
usty
, thi
ck-
ened
with
al
opec
ia,
prur
itis
Ears
, lat
eral
el
bow
s,
vent
ral
abdo
men
Zoon
otic
Sarc
opte
s sc
abei
v. s
uis
Pigs
Ina
mm
atio
n,
eryt
hem
a,
alop
ecia
, w
ith in
tens
e pr
uriti
s
Hea
d (e
ars,
no
se, e
yes)
in
itial
ly;
spre
ads
to
neck
, sho
ul-
ders
, bac
k
Zoon
otic
(con
tinue
s)
-
18 Arthropods
Tab
le 2
3(C
ontin
ued)
Mit
eH
ost
Lesi
ons
Com
mon
Sit
esO
ther
Not
oedr
es c
ati
Cat
s Ra
bbits
Yello
w c
rust
s,
thic
kene
d sk
in,
alop
ecia
Star
ts o
n ea
rs;
spre
ads
to
face
, nec
k,
paw
s, a
nd
hind
quar
-te
rs
Mos
t com
mon
ca
use
of fe
line
scab
ies
Trix
acar
us
cavi
aeG
uine
a pi
gsD
ry, s
caly
ski
n w
ith a
lope
-ci
a, d
erm
ati-
tis, e
xtre
me
prur
itis
Back
, nec
k,
shou
lder
sIn
fest
atio
ns c
an
lead
to
anor
exia
an
d de
ath
Cne
mid
ocop
tes
mut
ans
Poul
try
Wild
bird
sH
yper
kera
tosi
s w
ith le
gs
beco
min
g th
icke
ned,
de
form
ed
Legs
Com
mon
na
me:
sca
ly
leg
-
Arthropods 19
Cne
mid
ocop
tes
pila
e C
. jam
aice
nsis
Para
keet
s C
anar
ies
Leg
lesi
ons
as
for C
. m
utan
s;
crus
ty m
ass
on b
eak
Shan
ks a
nd
pads
of f
eet,
cere
, ven
t ar
ea, b
ack
Com
mon
na
me
for
faci
al le
sion
s =
sca
ly fa
ce
Cne
mid
ocop
tes
galli
nae
Poul
try
Pige
ons
Ina
mm
atio
n,
prur
itis;
fe
athe
rs
brea
k ea
sily
Back
, top
of
win
g, b
reas
t, th
ighs
, ven
t ar
ea
Bird
s m
ay
activ
ely
pull
out f
eath
ers
-
20 Arthropods
Tab
le 2
4H
ost,
Spec
ies,
Key
Cha
ract
eris
tics,
and
Les
ions
Cau
sed
by S
urfa
ce-
Dw
ellin
g Sa
rcop
tifor
m M
ites
Mit
eH
ost
Lesi
ons
Com
mon
Sit
esO
ther
Psor
opte
scu
nicu
liRa
bbits
Drie
d cr
ust i
n pi
nna;
bro
wn
disc
harg
e; o
ti-tis
med
ia m
ay
resu
lt
Ears
Can
als
o be
fo
und
on
hors
es, g
oats
, sh
eep
Psor
opte
s bo
vis
Cat
tlePr
uriti
c ar
eas
con-
sist
ing
of p
ap-
ules
, cru
sts,
th
icke
ned
skin
With
ers,
bac
k,
rum
pRe
porta
ble
and
quar
antin
able
Psor
opte
s ov
isSh
eep
Extre
mel
y pr
uriti
c;
cons
tant
rub-
bing
lead
s to
se
lf-m
utila
-tio
n; w
ool f
alls
ou
t; sk
in
Woo
led
area
s of
th
e bo
dyH
as b
een
erad
i-ca
ted
from
th
e U
nite
d St
ates
-
Arthropods 21
beco
mes
th
icke
ned,
cr
acks
, ble
eds
easi
ly; s
heep
be
com
e de
bil-
itate
d an
d ca
n di
eC
horio
ptes
sp
p.Ru
min
ants
H
orse
sSk
in b
ecom
es
thic
kene
d,
crus
ty; n
ot
over
ly p
rurit
ic
Skin
of l
ower
hi
nd le
gs, t
ail-
head
, esc
utch
-eo
n
Repo
rtabl
e in
so
me
stat
es
Oto
dect
es
cyan
otis
Dog
s C
ats
Ferre
ts
Inte
nsel
y pr
uriti
c;
muc
h da
rk
ceru
men
pro
-du
ced;
hea
d sh
akin
g ca
n ca
use
hem
atom
a of
th
e au
ral
pinn
a
Exte
rnal
ear
, ear
ca
nal;
has
been
foun
d ar
ound
the
base
of t
he
tail
If un
treat
ed, p
er-
fora
tion
of
the
tym
pani
c m
embr
ane
can
occu
r
-
Generalized demodecosis: occurs as a result of animmunodeficiency; diffuse alopecia, erythema, andsecondary bacterial infections; pruritic; rancid odor;difficult to ameliorate; poor prognosis.
Other Species These species are usually nonpatho-genic; however, lesions have been associated withinfestations. As for the dog, concomitant diseases areusually present with severe infestations.
Demodex cati and D. gatoi (cat) can cause alopecia, ery-thema, scaly or crusty dermatitis on face, neck, and ears.
Demodex bovis (cattle) and D. caprae (goats) can causepinhead and larger-sized pustules; found on theshoulders, trunk, and lateral aspect of the neck.
Demodex ovis (sheep) can cause localized, scalylesions; rare.
Demodex phylloides (pigs) can cause pustules aroundthe eyes and on the snout; can spread to ventral sur-face of the body.
Demodex caballi and D. equi (horses) may producepruritis, alopecia with scaling, or pustules; starts onthe neck or withers, spreading to head, forelimbs,and back.
Demodex aurati and D. criceti (hamsters, gerbils) cancause alopecia with scaling or scabs; found on therump and back (hamster) or face (gerbil).
22 Arthropods
-
PNEUMONYSSOIDES (=PNEUMONYSSUS) CANINUM Oval, pale yellow; 1.01.5 mm in length; all legs are
on the anterior half of the body.
Lives in nasal and paranasal sinuses of dogs; preva-lence in the United States is unknown.
Generally thought to be nonpathogenic; has beenassociated with sneezing, sinusitis, labored breath-ing, and disorders of the central nervous system (aresult of the sinusitis).
CHEYLETIELLA SPP. Species include Cheyletiella blakei (cats), C. parasitivo-
rax (rabbits), and C. yasguri (dogs).
Up to 386 266 m in size; have large hook-likeaccessory palpi on anterior end.
Mites are very motile; resemble moving flakes ofdandruff (common name: walking dandruff).
Causes a dry, scaly dermatitis; mild alopecia; perhapsskin thickening.
May infest humans causing a mild dermatitis.
DERMANYSSUS GALLINAE (RED MITE OF POULTRY) ANDORNITHONYSSUS SYLVIARUM (NORTHERN FOWL MITE)
Morphologically similar; approximately 1 mm inlength.
Parasitize chickens, wild birds; occasionally humans.
Arthropods 23
-
Ornithonyssus sylviarum usually found on birds, butalso can be found in nests and poultry houses; D. gal-linae usually found off birds.
Feeding activities cause irritation, weight loss, decreasedegg production, and anemia; may lead to death.
Diagnosis
The experienced clinician often can make an accurate diag-nosis based on the typical distribution and manner of thespread of lesions. However, a positive diagnosis depends onrecovery and identification of the mites. Skin scrapings,deep enough to draw blood, are the most common diag-nostic tool. Some mites are extremely difficult to find; there-fore, negative skin scrapings are inconclusive and animalsshould be examined repeatedly. Scrapings should be at themargins of active lesions. Additionally, for Demodex spp.,areas of normal skin should be scraped to determine if theinfection is generalized. For Cnemidocoptes spp., remove andexamine the underside of a loose scale. A strong hand lensmay be used to view Cheyletiella on the animal.
Table 25 presents a key to differentiate the commonsarcoptiform mites. Characteristic morphologic features ofnonsarcoptiform mites have already been presented.
Treatment and Control
Dogs and cats: oral or SQ ivermectin at 0.20.4 mg per kgor topical ivermectin at 0.5 mg per kg is effective against sar-
24 Arthropods
-
coptic mange in dogs. Clip hair and remove crusty materialwith keratolytic shampoo first. Ivermectin at 0.3 mg per kgand doramectin at approximately 0.3 mg per kg has beeneffective against notoedric mange in cats. Otodectic acaria-sis in dogs and cats requires a thorough cleaning of the earcanal followed by acaricidal otic solutions. Selamectin isapproved for use against this parasite. Oral (three treat-ments at weekly intervals) or SC (two treatments at 2 weeksapart) ivermectin at 0.20.4 g per kg is effective in dogs.Ivermectin at 0.20.5 g per kg administered orally, SC, ortopically is effective in cats. Treatment intervals for oral andSC in cats is as for dogs; use a minimum of two treatmentsgiven 2 weeks apart for pour-on. For demodectic mange indogs, the localized form has been treated with 1% rotenone
Arthropods 25
Table 25 Key to the Genera of Common Sarcoptiform Mites
1a. Short, unjointed pedicels. . . . . . . . . . . . . . . . . . . . . . . . . 2 1b. Long pedicels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2a. Pedicels on rst, second, and fourth pairs of legs of
females and all legs of males; body of males with large, posterior lobes . . . . . . . . . . . . . . . . . . . . . . . . . .Chorioptes
2b. Pedicels on rst and second pairs of legs of females and all legs of males; body of male with small, posterior lobes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Otodectes
3a. Long, jointed pedicels . . . . . . . . . . . . . . . . . . . . Psorpotes 3b. Long, unjointed pedicels . . . . . . . . . . . . . . . . . . . . . . . . . 4 4a. Anus at posterior margin of body . . . . . . . . . . . Sarcoptes 4b. Anus on dorsal surface of body . . . . . . . . . . . . Notoedres
-
ointment or 5% benzoyl peroxide once or twice daily. Donot use Amitraz for treatment of the localized form. How-ever, Amitraz is approved and recommended for use againstthe generalized form. Continue treatment until no livemites are found on two successive skin scrapes. Daily oralivermectin at 0.6 mg per kg until resolution of infection (4months) and daily oral milbemycin oxime at 0.523.8 mgper kg for varying periods has also been used with mixedsuccess. For P. caninum, milbemycin oxime at 0.51.0 mgper kg orally once a week for 3 weeks was effective. ForCheyletiella, acaricidal shampoos approved for use on dogsor cats are effective as is fipronil in dogs. Ivermectin at0.20.4 mg per kg every 7 (orally) or 14 (SQ) days for 68weeks or pour-on ivermectin at 0.5 mg per kg given 2 weeksapart has also been used. Be sure to treat premises withresidual acaricidal spray.
Ruminants: acaricides effective against lice are alsogood for chorioptic mange in cattle. Eprinomectin isapproved for use in lactating dairy cattle. Sarcopticmange is reportable in cattle; should it occur, treatmentand control requirements will be outlined at that time.Psoroptic mange is also reportable and treatment andcontrol requirements will be outlined at that time.
Horses: lindane applied two times at weekly intervalshas been effective. Thoroughly clean stall and associatedequipment (e.g., feed buckets, curry combs).
Pigs: ivermectin at 0.3 mg per kg SQ is used againstsarcoptic mange.
Birds: efforts against D. gallinae are directed towards theenvironment. Periodic removal of litter and nest materials,
26 Arthropods
-
thorough cleaning, and high-pressure application ofresidual acaricides are recommended. For control of O.sylviarum, spray birds with appropriate ectoparasiticidesuch as malathion, carbaryl, or permethrin. As with allmedications, read and follow label directions. Cnemido-coptic mites may be treated with ivermectin at 0.2 mg perkg, administered parenterally or orally.
Guinea pigs: T. caviae can be treated with two dosesof ivermectin at 0.20.5 mg per kg SQ or orally, given 1week apart.
Rabbits: P. cuniculi can be treated with two injectionsof ivermectin at 0.20.4 mg per kg given 2 weeks apart.
Lice (Insecta)Lice are distributed across two orders, the Anoplura (suck-ing lice) and the Mallophaga (biting or chewing lice). Table26 outlines the important characteristics of each family.Although geographic distribution varies according to eachspecies of louse, in general, lice are distributed worldwide.
Life Cycle
Simple metamorphosis with nymphal stages resem-bling adults.
Spend entire life on the host; transmission primarilyby direct contact, but fomites can also play a role.
Separate sexes with adult females laying small(0.51.0 mm), whitish, oval eggs (nits); attachedfirmly to hair or feathers.
Arthropods 27
-
28 Arthropods
Tab
le 2
6Im
port
ant C
hara
cter
istic
s D
istin
guis
hing
the
Two
Ord
ers
of L
ice
Char
acte
rA
nop
lura
(Su
ckin
g Li
ce)
Mal
lop
hag
a (C
hew
ing
Lice
)
Col
orTe
nd to
be
gray
or r
ed d
epen
ding
on
how
muc
h bl
ood
has
been
in
gest
ed
Tend
to b
e ye
llow
Mou
thpa
rtsPi
erci
ng m
outh
parts
Che
win
g m
outh
parts
H
ead
Som
ewha
t poi
nted
, nar
row
er th
an
thor
axRo
unde
d he
ad, b
road
er th
an
thor
ax
Life
sta
ges
Egg,
thre
e ny
mph
s, a
dult
Egg,
thre
e ny
mph
s, a
dult
Atta
chm
ent
Tend
s to
rem
ain
atta
ched
to a
nim
alTe
nds
to b
e m
obile
, eas
y to
re
mov
e
-
Nymphs hatch from eggs; three nymphal stagesoccur prior to reaching the adult stage.
After mating, the adult female will lay eggs and thelife cycle begins again.
The time from egg to egg can take as little as 34 weeks.
Eggs generally do not hatch and neither nymphs noradults will live much longer than 1 week if removedfrom the host.
Common Lice
Lice are relatively host specific with most species ofanimals having some type of louse (common speciesand hosts are presented in Table 27); human lice(Phthirus pubis, Pediculus humanus) can occasionallybe found on dogs.
Sucking lice do not parasitize cats or birds.
Importance
Most lice problems manifest under crowded condi-tions, often in winter.
The presence of either type of louse can cause irri-tation, pruritis, scratching, licking, and restlessnessleading to loss of condition, poor weight gain,decreased milk production, etc.
Sucking lice can cause anemia.
Bite wounds can become secondarily infected.
Arthropods 29
-
30 ArthropodsTa
ble
27
Com
mon
Spe
cies
of C
hew
ing
(Ord
er: M
allo
phag
a) a
nd S
ucki
ng
(Ord
er: A
nopl
ura)
Lic
e As
soci
ated
with
Dom
estic
Ani
mal
s
Hos
tCh
ewin
g Lo
use
Suck
ing
Lou
se
Bird
sM
enop
on s
pp. (
poul
try)
Gon
oide
s sp
p. (
poul
try)
Col
umbi
cola
spp
. (pi
geon
s)
Non
e
Cat
sFe
licol
a su
bros
tratu
sN
one
Dog
sTr
icho
dect
es c
anis
Lino
gnat
hus
seto
sus
Swin
eN
one
Hae
mat
opin
us s
uis
Shee
pD
amal
inia
(=
Bov
icol
a) o
vis
Lino
gnat
hus
peda
lis (
also
goa
ts)
Lino
gnat
hus
ovill
us (
also
goa
ts)
Goa
tsD
amal
inia
(=
Bov
icol
a) c
apra
e D
amal
inia
(=
Bov
icol
a) li
mba
taLi
nogn
athu
s st
enop
sis
Lino
gnat
hus
afric
anis
Hor
ses
Dam
alin
ia (
=B
ovic
ola)
equ
iH
aem
atop
inus
asi
ni
Cat
tleD
amal
inia
(=
Bov
icol
a) b
ovis
Hae
mat
opin
us e
urys
tern
us
Lino
gnat
hus
vitu
liSo
leno
pote
s ca
pilla
tus
Rats
/mic
eN
one
Poly
plax
spi
nulo
sa/P
olyp
lax
serr
ata
Gui
nea
pigs
Glir
icol
a po
rcel
li G
yrop
us o
valis
Non
e
Ger
bils
Non
eH
oplo
pleu
ra m
erid
ioni
dis
-
Trichodectes canis is an intermediate host of Dipylidiumcaninum; Linognathus setosus is an intermediate hostfor Acanthocheilonema reconditum; Haematopinus suistransmits swine pox and probably Eperythrozoon.
Diagnosis
Lice and their eggs can be detected through carefulexamination of hair or feathers and are easily seen withthe naked eye. A hand-held magnifying lens may assist intheir visualization.
Treatment and Control
Dogs and cats: carbaryl shampoos, sprays, or dips, appliedin two treatments at 1 week intervals, are effective.
Beef and nonlactating dairy cattle: numerous sprays,dips, and pour-ons are available for use against lice as areinsecticidal ear-tags. Macrolide injectibles and pour-onshave excellent activity against anopluran infestations andpour-ons also work against mallophagans. If a herd has ahistory of infestation, fall treatment is recommended toavoid winter increase in lice populations. Beware of poten-tial host-parasite reactions to cattle grubs that may be con-currently in the esophagus or spinal canal (see Hypoderma).
Lactating dairy cattle: a few compounds that can beapplied as sprays or used in back rubbers or dust bags areavailable for this group of animals. Eprinomectin is alsoapproved and has no withdrawal time.
Arthropods 31
-
Pigs: injectible or premix formulations of avermectins orpour-on organophosphates are available for lice control.
Horses: two spray applications of coumaphos 2 weeksapart are effective. Dusting horses with a mixture of rotenoneand a synergized pyrethrin in winter may be less stressful.
Fleas (Insecta)Adult fleas are wingless, laterally compressed insects withpowerful hind legs allowing them to jump great dis-tances. They have piercing-sucking mouthparts thatenable them to feed on a hosts blood by piercing ablood vessel and imbibing the blood from the lumen.
Life Cycle
Complex metamorphosis with egg, maggot-like lar-val stages, pupa, and adults.
Adults are parasitic; other stages are found primarilyin the hosts environment.
Separate sexes with adult females laying small (about0.5 mm long), oval eggs on the host or in the envi-ronment.
Larvae hatch from eggs; three larval stages growingfrom about 2 mm to 5 mm in size, white, turningbrown after feeding (primarily on flea feces).
Third larval stage pupates; pupal stage is stage most resis-tant to environmental stress and chemical control efforts.
32 Arthropods
-
Heat, carbon dioxide, and movement stimulateadults to emerge from pupae.
Fleas tend to survive best in humid conditions.
Fleas Encountered in North America
CTENOCEPHALIDES FELIS AND CTENOCEPHALIDES CANIS Parasitize a wide variety of mammals; will feed on humans.
Ctenocephalides felis is the most commonly encountered fleaof cats and dogs.
Generally distributed throughout the United States, par-ticularly prevalent in humid areas.
Life cycle can take as little as 3 weeks or as long as 20months.
Feeding causes irritation resulting in the animal bit-ing and scratching; can cause anemia in very heavyinfestations.
Some animals become sensitized to the salivarysecretions resulting in an intensely pruritic reaction(flea-bite hypersensitivity or flea allergy dermatitis).
Intermediate host for Dipylidium caninum, Acan-thocheilonema reconditum; transmits Bartonella henselae(cat scratch fever).
ECHIDNOPHAGA GALLINACEA (STICKTIGHT FLEA) Parasitize poultry and other domestic birds; will feed
on dogs, cats, rabbits, horses, and humans.
Arthropods 33
-
Present in United States as far north as Kansas andVirginia.
Life cycle completed in 3060 days.
Females remain attached at site of feeding; causesswelling and ulceration; if near eyes, lesions maycause blindness.
XENOPSYLLA CHEOPIS (ORIENTAL OR TROPICAL RAT FLEA) Parasitize rats; will feed on humans.
Present in United States as far north as the northern-most states.
Life cycle completed in as little as 3 weeks.
Primary importance is as vector of plague (Yersinia pestis).
PULEX IRRITANS (HUMAN FLEA) Parasitize humans; will feed on dogs, cats, pigs, and
rats.
Life cycle takes about 1 month to complete.
This is a human parasite capable of transmittingplague; when recovered from a pet, must tactfullyexplain to the owners they are the reason the animalhas fleas.
Treatment and Control
Dogs and cats: lufenuron, fipronil, and imidaclopridhave dramatically changed flea control. All can be
34 Arthropods
-
administered at monthly intervals although lufenuronalso has a long-acting injectible formulation providingaction longer than a 1-month duration. Lufenuron doesnot kill adult fleas, but prevents eggs from hatching.Because the vast majority of all fleas are found in theenvironment as eggs, larvae, or pupae, environmentalcontrol should be considered in flea control programswith these or any other products. Numerous over-the-counter products are available as shampoos, collars, ortopicals, which provide adequate control when com-bined with proper environmental control programs.
Myiasis-Producing Flies (Insecta)The larvae of certain dipterans are capable of developingin the tissues of many domestic animals. This results in acondition called myiasis. There are two types of myiases:(1) facultative myiasislarvae are free-living, but canbecome parasitic under certain conditions; and (2) obligatory myiasislarvae are always parasitic, i.e., withouta proper host, the flies cannot complete their life cycle.
Life Cycle
Complex metamorphosis with egg, larval stages(instars), pupa, and adults.
Separate sexes with adult females laying eggs or lar-vae on host or in environment.
Larvae hatch from eggs; three larval stages (maggots).
Arthropods 35
-
Third larval stage pupates with adults emergingfrom pupae.
Obligatory Myiasis-Producing Flies
Adults of the obligatory myiasis-producing flies tend toresemble honeybees. They have only vestigial mouthpartsand, therefore, do not feed. They are quite annoying totheir hosts as the females buzz around the animal, layingher eggs. These flies are extremely host- and site-specific.Because they are so specific, the third-stage larvae can beprovisionally identified to genus based on host and sitealone. However, first- and second-stage larvae must be dif-ferentiated from larvae of the facultative myiasis- producing flies, particularly if in an abnormal host.
OESTRUS OVIS (SHEEP NASAL BOT) Females fly around nostrils of sheep and goats during
the hottest part of the day; deposit tiny, white to yellow,first-stage larvae; crawl into nasal sinuses, and developinto large (3 cm), dark brown third-stage larvae.
Third-stage larvae crawl out of the nostrils or aresneezed out; pupate in the ground; adults emerge36 weeks later; if begin pupating in fall, pupateoverwinter and adults emerge in spring; larvae canalso overwinter in nares of host.
Larvae produce a purulent rhinitis or sinusitis leading tohead shaking, restlessness, snorting; may lead to dam-age of cribriform plate and subsequent brain injury.
36 Arthropods
-
Diagnosis based on seeing large, dark brown larvaedropping out of nostrils; postmortem diagnosisachieved by sawing skull in half longitudinally, rins-ing key areas with water, and examining the rinsingsfor larvae with a magnifying lens.
Ocular myiasis of humans has been reported.
GASTEROPHILUS (OR GASTROPHILUS) SPP. (HORSE STOMACH BOT)
Three species in horsesG. nasalis, G. hemorrhoidalis,G. intestinalis.
Adult females attach elongate, operculated eggs tohairs of the intermandibular space (G. nasalis), thelips (G. hemorrhoidalis), or forelegs and shoulders (G.intestinalis) during late summer and early fall.
Eggs around the mouth hatch spontaneously; thoseelsewhere hatch in response to sudden warmth pro-vided by the breath of the horse.
Larvae penetrate and migrate in oral mucosa andtongue; eventually reach the stomach or duodenumand attach to the wall.
Third-stage larvae pass out in feces in spring; pupatein the soil for 39 weeks.
Generally considered benign parasites except forthe annoyance associated with the adults; mucosaland submucosal inflammation and mucosal ulcera-tion of the duodenum has been associated withinfections of G. nasalis in ponies.
Arthropods 37
-
Diagnosis is based on seeing eggs attached to hairsor distinctive third-stage larvae in feces; one can alsofind larvae at necropsy; usual attachment sites arethe first ampulla of the duodenum for G. nasalis, thenonglandular part of the stomach at the margo pli-catus or in the saccus cecus for G. intestinalis, theduodenum and rectum for G. hemorrhoidalis.
HYPODERMA SPP. (CATTLE GRUBS; HEEL FLIES) Two species infesting cattle and bisonH. bovis
(northern cattle grub), H. lineatum (common orsouthern cattle grub).
Hypoderma lineatum is present in the southern UnitedStates; both species are present in the northernUnited States and into Canada.
Entire life cycle of both species takes about 1 year tocomplete.
Adult H. lineatum becomes active with the start ofwarm weather, remaining active for about 2 months;H. bovis becomes active about the time H. lineatumstops, remaining active into summer.
Larvae hatch spontaneously, crawl down hair shaft,penetrate skin, and migrate through the subcuta-neous tissues.
Larvae, in 45 months, come to rest in either thesubmucosal connective tissue of the esophagus (H.lineatum) or the epidural fat (H. bovis); remain therefor about 3 months.
38 Arthropods
-
Resume migration to subcutaneous tissues of theback, cut breathing holes and increase in size as theydevelop to the third-stage larvae.
When fully developed, larvae exit through breathingholes, fall to ground, and pupate with adult fliesemerging in 45 weeks.
Egg-laying activity disturbs animals; they run aboutaimlessly (gadding) in an attempt to escape the flies;results in loss of production.
Larval infestation leads to carcass damage and dam-age to hide from the breathing holes; if animals aretreated when larvae are in resting sites (esophagus,spinal canal), signs of bloat/choke or central ner-vous system disease can result.
Diagnosis is made by finding either the eggs on hairsof the legs or the larvae in the back.
Infestations of horses and humans have beenreported, although rare.
COCHLIOMYIA HOMINOVORAX(AMERICAN PRIMARY SCREWWORM)
Only fly in North America attracted to unconta-minated skin wounds of domestic animals; willinfest any living warm-blooded animal (includinghumans) with a wound.
Adult females lay many eggs in batches of 15400 atthe edge of wounds.
Arthropods 39
-
Larvae hatch spontaneously and enter wound feed-ing on secretions and living flesh; become third-stage larvae in 57 days.
Larvae drop to ground, burrow in soil and pupate;adults emerge in one to several weeks.
Life cycle can be completed in as little as 24 days; lar-vae cannot overwinter where soil freezes.
Fatal if not treated; can kill a full-grown steer in 57days.
Massive eradication efforts used insecticidal treatmentof all infested animals and release of sterile flies to elim-inate this parasite from the United States and Mexico.Because females mate once and the wild population ofthe fly is relatively small, release of billions of sterilemales swamps the population and significantly reducesthe chance of a successful mating.
Occasionally reenters the United States in importedanimals; larvae encountered in wounds (particularlyof imported animals or animals in border areas withMexico) must be differentiated from facultative myi-asis-producing flies. If encountered, it must bereported to state and federal authorities.
CUTEREBRA SPP. Primarily parasites of rabbits and rodents; will infest
dogs and cats; although rare, most frequent cause ofendemic human myiasis in North America.
40 Arthropods
-
Adult females lay eggs near entrances to burrows oralong rabbit runs.
Larvae hatch in response to presence of animal,crawl into fur, and enter subcutaneous tissues of hostthrough natural body openings.
Cut breathing holes and develop to large (up to 3cm), black third-stage larvae in subcutaneous cysts.
In dogs and cats, generally found in neck and headregion in late summer and early fall; also found inaberrant sites including anterior chamber of the eyeand the brain.
Generally benign unless secondary bacterial infec-tion of cyst occurs or larvae migrate to aberrant sites.
Diagnosis is based on finding characteristic cysts withbreathing holes in which second- or third-stage lar-vae are usually present.
Facultative Myiasis-Producing Flies
GENERA OR SPECIES INVOLVED Lucilia (green or copper bottle flies)
Phoenicia (green bottle flies)
Phormia (black blow flies)
Calliphora (blue bottle flies)
Sarcophaga (flesh flies)
Cochliomyia macellaria (secondary screwworm)
Arthropods 41
-
IMPORTANCE Normally, adults lay eggs in carrion or feces; also
attracted by suppurative wounds, necrotic areas, skinsoiled with urine, feces, or vomitus (bacterial growthgenerates odors attractive to flies); condition calledfly strike or strike.
Females feed and lay eggs; larvae hatch; feed onnecrotic debris and exudates.
Larvae can cause further damage; some may invadehealthy subcutaneous tissue producing large cavitiesor tunnels; host becomes anorexic and weak.
Infestation can lead to death as a result of sep-ticemia, toxemia, or shock.
DIAGNOSIS Diagnosis of maggot infestation is not diffi-cult because the larvae are easily observed in the wound orwithin the hair coat. Species diagnosis, however, is depend-ent on morphologic characteristics of the larvae, particu-larly of the spiracular plates on the posterior end of thelarvae. Depending on the situation, larvae may need to bedifferentiated from those of Cochliomyia hominivorax. Inthat case, collect larvae, preserve in 70% ethanol, and sub-mit to proper authorities for identification.
Treatment and Control
For bots of sheep, horses, and grubs of cattle, avermectins areeffective. Treatment of cattle should be done immediatelyafter fly season ends but before the larvae reach the esopha-
42 Arthropods
-
gus or spinal cord; destruction of larvae in these tissuescauses severe inflammatory reactions and clinical signs cor-responding to the locality of the larvae. The danger periodfor treatment is estimated to be 68 weeks before the larvaeappear in the back, which occurs around mid-September inthe southern United States, late December in areas such asOhio, and late January in the more northern areas of theUnited States. Although adverse reactions are considered tobe rare occurrences these days, they must still be kept inmind in designing parasite control programs for cattle.
Infestations of C. hominivorax are reportable; shouldit occur, treatment and control requirements will be out-lined at that time.
Treatment of Cuterebra consists of manual extractionof the larva.
Treatment of facultative myiasis infestations includesdebriding area, applying appropriate insecticides, and, ifpresent, treating secondary bacterial infections.
Keds (Insecta)This is a group of dorso-ventrally flattened insects thatmay or may not have wings. Although there are numer-ous species of keds in North America, only one is gener-ally encountered in veterinary medicine.
Melophagus ovinus (Sheep Ked)
Entire life cycle spent on sheep or goats; transmis-sion is by direct contact although fed females maylive up to a week off the host.
Arthropods 43
-
No eggs present on host; larvae retained inabdomen until ready to pupate; time until adultemergence depends on ambient temperature.
Most numerous in cold months (fall, winter) withfewer present during warm months; more prevalentin northern United States and Canada.
Feed on blood which may cause anemia; bites arealso pruritic leading to biting, scratching, and rub-bing which damages wool; ked feces stains wool,decreasing value.
Coumaphos, malathion, and other insecticides areeffective against this parasite.
Biting Gnats and Mosquitoes (Insecta)These dipteran insects are periodic parasites; that is, theonly role vertebrate hosts have in the insects life cycle isas a food source for the adult females. However, theseinsects have a primary role as biological vectors of variousdisease-causing agents. Because the insects are only peri-odic parasites, they are usually not found on the animals.
Life Cycle
Complex metamorphosis with egg, up to five larvalstages, pupa, and adults.
Separate sexes with adult females laying eggs inaquatic or semi-aquatic habitats.
44 Arthropods
-
Larvae hatch from eggs; final larval stage pupates;adults emerge.
Adult females need bloodmeal for egg development;males do not feed on blood.
Simulium spp. (Black Flies; Buffalo Gnats)
Tiny flies (16 mm long) that tend to swarm;require well-aerated water for eggs; limits geo-graphic distribution to areas of swiftly runningwater.
Serrated, scissor-like mouthparts; lacerates tissue toform a pool of blood; bites very painful; ears, neck,and abdomen are favored feeding sites.
Swarming and biting can cause annoyance, resultingin decreased production in livestock.
Transmit Leucocytozoon spp. (hemoparasites of birds),Onchocerca gutterosa.
Culicoides spp. (No-See-Ums, Biting Midges)
Tiny gnats (13 mm long); habitat requirementsvary with species; strong fliers that tend to remainclose to breeding grounds; active at dusk or dawn.
Bites are very painful; favored feeding sites are eitheron dorsal or ventral aspect of host, depending onspecies involved.
Bites cause annoyance.
Arthropods 45
-
Allergic dermatitis in horses; begins as discretepapules on dorsum; areas of alopecia form as hairmats, crusts, then falls off; intensely pruritic leadingto scratching and rolling behavior which may lead toinjury or secondary infection.
Transmit bluetongue virus, Onchocerca cervicalis, Haemo-proteus, and Leucocytozoon spp. (hemoparasites of birds).
Anopheles spp., Aedes spp., Culex spp. (Mosquitoes)
Small flies (36 mm long) that tend to swarm; layeggs on water or in dry places that flood periodically;complete entire life cycle in as little as 12 weeks.
Have piercing-sucking mouthparts; pierces blood ves-sel and feeds from the lumen; bites can be painful.
Swarming and biting can cause annoyance leading todecreased production in livestock; rarely causes anemia.
Transmit eastern and western equine encephalitis,Plasmodium species (malaria), Dirofilaria immitis.
Treatment and Control
Because these pests are not found on the host exceptwhen feeding, insecticidal treatment is ineffective unlessrepeated every few days; this becomes too expensive andimpractical. Consequently, control is aimed at killingpre-adult stages.
46 Arthropods
-
Horse Flies, Deer Flies (Insecta)Like mosquitoes and biting gnats, horse flies and deerflies are periodic parasites in which only the adultfemales feed on blood.
Life Cycle
Complex metamorphosis with egg, larval stages,pupa, and adults.
Separate sexes with adult females laying eggs inaquatic or semi-aquatic habitats.
Larvae hatch from eggs, drop into the water or mud;first- and second-stage larvae do not feed; later stagesfeed on insect larvae, snails, young frogs, organicmatter, etc.; in temperate regions, larvae may over-winter and pupate the following spring.
Pupae are found in dry soil; adults are active onlyduring warmer months in temperate regions.
Adult females need blood for egg development;interrupted feedersfeeds several times in multiplesites on one or more hosts until replete; preferredfeeding sites are ventral abdomen, legs, neck, with-ers; prefers feeding on larger animals.
Genera Involved
Tabanus (horse flies)
Chrysops (deer flies)
Arthropods 47
-
Importance
Large flies (up to 3.5 cm with horse flies being big-ger than deer flies).
Bite very painful; scissor-like mouthparts lacerate tissueto form pool of blood; bite causes restlessness, annoy-ance, avoidance behavior, which interferes with grazingand resting resulting in decreased production.
Mechanical vectors of anaplasmosis, anthrax, equineinfectious anemia virus.
Tabanus spp. are intermediate hosts for Elaeophoraschneideri (arterial worm of deer, elk, sheep).
Treatment and Control
Difficult to kill or repel. Flies rarely enter roofed areas sostabling during hours of peak fly activity helps. Keepinganimals inside a fence 2.4 m in height with a 0.6 cm meshhelps reduce the attack rate. Keep grazing animals awayfrom the edge of wooded areas also helps reduce theattack rate.
Stable Flies, Horn Flies, Face Flies (Insecta)These flies are periodic parasites with different feedinghabits. Both male and female stable and horn flies feedon blood whereas only female face flies feed on mucus,saliva, and tears.
48 Arthropods
-
Life Cycle
Complex metamorphosis with eggs, larvae, pupae,and adults.
Separate sexes with adult females laying eggs indecaying organic matter (stable fly) or fresh cowmanure (horn fly, face fly).
Larvae hatch from eggs; final larval stage pupates;adults emerge.
Stomoxys calcitrans (Stable Fly)
Flies similar in size to house fly (67 mm long);piercing-sucking mouthparts.
Distributed primarily in central and southeasternUnited States.
Horse preferred host, but will feed on most domes-tic animals and humans; feed 12 times per daydepending on ambient temperature; feed primarilyon legs and flanks of cattle and horses, ears of dogs,ankles of humans.
Bites are painful; annoyance can lead to decreasedproduction in livestock.
Mechanical vectors of anthrax and equine infectiousanemia virus; intermediate host for Habronemamicrostoma (stomach nematode of horses).
Arthropods 49
-
Haematobia irritans (Horn Fly)
Dark-colored, small flies (36 mm long); piercing-sucking mouthparts.
Distributed throughout North America.
Feed on cattle; rarely on horses, sheep, dogs.
Adults spend most of life on host, leaving only to layeggs; adults cluster on shoulders, back, and sides; ifambient temperature < 70F, cluster around base ofhorns; if quite hot, cluster on ventral abdomen.
Irritation associated with feeding activities results inlost beef and/or dairy production; of all blood-suck-ing flies in the United States, this fly is most respon-sible for reduced weight gains and milk production.
Intermediate host for Stephanofilaria stilesi (filaridnematode of cattle).
Can cause a focal, midline dermatitis in horses.
Musca autumnalis (Face Fly)
Medium-sized flies (about 6 mm long); spongingmouthparts.
Generally distributed in North America except forthe southwestern United States; adults will hibernatein large groups inside buildings.
Feed on all types of livestock, horses, and bison.
Flies feeding activity is irritating to the host; canlead to decreased production.
50 Arthropods
-
Mechanical vectors of infectious keratoconjunctivitis(pinkeye).
Intermediate host for Thelazia spp. (eyeworms) ofcattle.
Treatment and Control
Treatment with insecticides is possible; read the labeland follow directions carefully. Insecticidal ear tags canbe effective fly control aids. Pour-on avermectins areeffective against horn flies
Arthropods 51
-
3Introduction to the Endoparasites
Endoparasites are those parasites that live within the bodyof the host. There are four major groups of endoparasitesnematodes, acanthocephalans, platyhelminths (trematodesand cestodes), and protozoans. Table 31 provides distin-guishing characteristics of the helminthic parasites.
NematodesAppearance and Morphology
Variable length, 1 mm to several meters.
Body covered with cuticle, may form specializedstructures (e.g., alae).
Usually sexually dimorphic with males smaller thanfemales.
53
-
54 Introduction to the Endoparasites Ta
ble
31
Cha
ract
eris
tics
of th
e M
ajor
Hel
min
th G
roup
s
Char
acte
rist
icP
hyl
um
Nem
ath
elm
inth
esA
can
thoc
eph
ala
Pla
tyh
elm
inth
es
Cest
odes
Trem
atod
es
Body
sha
peRo
und,
elo
n-ga
te, g
ener
ally
ta
perin
g at
bo
th e
nds,
not
se
gmen
ted
Roun
d, e
lon-
gate
, ant
erio
r w
ith s
piny
pr
obos
cis,
ap
pear
s to
be
segm
ente
d
Dor
so-v
en-
trally
at
-te
ned,
el
onga
te,
segm
ente
d
Dor
so-v
en-
trally
at
-te
ned,
leaf
-sh
aped
, not
se
gmen
ted
Coe
lem
Pseu
doco
elPs
eudo
coel
Acoe
lom
ate
Acoe
lom
ate
Dig
estiv
e tra
ctC
ompl
ete
(mou
th,
esop
hagu
s,
inte
stin
e, a
nus)
Abse
ntAb
sent
Inco
mpl
ete
(mou
th,
esop
hagu
s,
inte
stin
e)
Sexe
sD
ioec
ious
(s
epar
ate
sexe
s)
Dio
ecio
usM
onoe
ciou
s (h
erm
aphr
o-di
tic)
Mon
oeci
ous
(exc
eptio
ns)
-
Classification
Nematodes are divided among two classes: the Secer-nentea and the Adenophorea. The Adenophorea con-tains the whipworms, capillarids, and Trichinella spiralis,while the Secernentea contains the remainder of the par-asitic nematodes. Numerous advancements have beenmade in our understanding of the relationships of manyof these parasites. As a consequence, some nematodeshave been reassigned to different genera (Table 32).While some consider presenting current and future vet-erinarians with proper taxonomic nomenclature to beimpractical, others consider not to do so to be a disser-vice to their continuing education and development.Therefore, those changes in species level nomenclaturewhich have achieved general acceptance among the sci-entific community are presented herein. Tables 33, 34,35, 36, and 37 present the orders, families, andspecies of the parasitic nematodes by host group.
Life Cycle
All nematodes, whether parasitic or free-living, havethe same stages in the life cycle: egg, four larvalstages (L1 molts to L2 molts to L3 molts to L4), imma-ture adult (sometimes called L5), which matures intoadult.
Stages occurring in the external environment are sub-jected to stresses (temperature, desiccation, sunlight,etc.) that may kill or delay development (develop-
Introduction to the Endoparasites 55
-
56 Introduction to the Endoparasites
Tab
le 3
2Re
clas
sic
atio
n of
Som
e Pa
rasi
tes
Impo
rtan
t to
Vete
rinar
y M
edic
ine
Old
Nam
eN
ew N
ame
Inte
rmed
iate
/Pa
rate
nic
Hos
tD
en
itiv
e H
ost
Site
of
Infe
ctio
n
Cap
illar
iaae
roph
ilaEu
cole
usae
roph
ilus
Earth
wor
mC
anid
s, fe
lids,
m
uste
lids
Lung
s
Cap
illar
ia
bhm
iEu
cole
us
bhm
iN
one
know
nFo
x, d
ogN
asal
, par
ana-
sal s
inus
es
Cap
illar
ia p
lica
Pear
sone
ma
plic
aEa
rthw
orm
Can
ids,
mus
-te
lids
Urin
ary
blad
der
Cap
illar
ia
felis
cati
Pear
sone
ma
felis
cati
Earth
wor
mFe
lids
Urin
ary
blad
der
Cap
illar
ia
puto
riiAo
ncho
thec
apu
torii
Earth
wor
mM
uste
lids,
ra
ccoo
n,
pig,
cat
Stom
ach,
smal
l in
test
ine
Cap
illar
ia b
ovis
Aonc
hoth
eca
bovi
sN
one
know
nC
attle
Smal
l int
estin
e
-
Introduction to the Endoparasites 57
Cap
illar
iaan
nula
tus
Euco
leus
an
nula
tus
Earth
wor
mC
hick
ens,
w
ild g
ame
bird
s
Esop
hagu
s,
crop
Cap
illar
ia
cont
ortu
sEu
cole
us
cont
ortu
sN
one
orea
rthw
orm
Wid
e va
riety
of
bird
sEs
opha
gus,
cr
op,
mou
th
Cap
illar
ia
obsi
gnat
aB
arus
capi
llaria
ob
sign
ata
Non
eW
ide
varie
ty
of b
irds
Smal
l int
estin
e
Dip
etal
onem
a re
cond
itum
Acan
tho-
chei
lone
ma
reco
nditu
m
Flea
s, li
ceC
anid
sSu
bcut
aneo
us
tissu
es
Toxo
cara
cat
iTo
xoca
ram
ysta
xRo
dent
sFe
lids
Smal
l int
estin
e
Ost
erta
gia
circ
umci
ncta
Tela
dors
agia
circ
umci
ncta
Non
eRu
min
ants
, es
peci
ally
sh
eep
Abom
asum
Bab
esia
equ
iTh
eile
ria e
qui
Ixod
id ti
cks
Hor
ses
Red
bloo
d ce
lls
-
58 Introduction to the Endoparasites Ta
ble
33
Cla
ssi
catio
n of
Nem
atod
es E
ncou
nter
ed in
Pig
s
Clas
sO
rder
Fam
ily
Spec
ies
Sece
rnen
tea
Rhab
ditid
aSt
rong
yloi
dida
eSt
rong
yloi
des
rans
omi
Stro
ngyl
ida
Tric
host
rong
ylid
aeH
yost
rong
ylus
rub
idus
St
rong
ylid
aeO
esop
hago
stom
um d
enta
tum
; O
. bre
vica
dum
Sy
ngam
idae
Step
hanu
rus
dent
atus
M
etas
trong
ylid
aeM
etas
trong
ylus
apr
i; M
. pud
en-
dode
ctus
; M. s
alm
i As
carid
ida
Asca
ridiid
aeAs
caris
suu
m
Spiru
rida
Spiro
cerc
idae
Asca
rops
stro
ngyl
ina
Phys
ocep
halu
s se
xala
tus
Aden
opho
rea
Enop
lida
Tric
hurid
aeTr
ichu
ris s
uis
Tric
hine
llida
eTr
ichi
nella
spi
ralis
-
Introduction to the Endoparasites 59
Tab
le 3
4C
lass
ica
tion
of N
emat
odes
Enc
ount
ered
in H
orse
s
Ord
erFa
mil
ySp
ecie
s
Rhab
iditi
daSt
rong
yloi
dida
eSt
rong
yloi
des
wes
teri
Hal
icep
halo
bus
(=M
icro
nem
a) d
elet
rix*
Rhab
ditis
(=
Pelo
dera
) st
rong
yloi
des*
* Not
men
tione
d fu
rther
in th
is b
ook.
Stro
ngyl
ida
Dic
tyoc
aulid
aeTr
icho
stro
ngyl
idae
Dic
tyoc
aulu
s ar
nel
di
Tric
host
rong
ylus
axe
i St
rong
ylid
aeSt
rong
ylus
vul
garis
; S.
eden
tatu
s; S
. equ
inus
C
yath
osto
mum
spp
. and
ot
her s
mal
l stro
ngyl
es
Asca
ridid
aAs
carid
iidae
Para
scar
is e
quor
um
Oxy
urat
aO
xyur
idae
Oxy
uris
equ
i Sp
irurid
aH
abro
nem
atid
aeD
rasc
hia
meg
asto
ma
Hab
rone
ma
mus
cae;
H
. mic
rost
oma
Thel
aziid
aeTh
elaz
ia la
crym
alis
O
ncho
cerc
idae
Onc
hoce
rca
cerv
ical
is
-
60 Introduction to the Endoparasites
Tab
le 3
5C
lass
ica
tion
of N
emat
odes
Enc
ount
ered
in R
umin
ants
Clas
sO
rder
Fam
ily
Spec
ies
Sece
rnen
taRh
abdi
tida
Stro
ngyl
oidi
dae
Stro
ngyl
oide
s pa
pillo
sus
Stro
ngyl
ida
Tric
host
rong
ylid
aeO
ster
tagi
a os
terta
gia;
* Te
lado
rsag
ia c
ircum
cinc
ta
Tric
host
rong
ylus
axe
i; T.
col
ubrif
orm
is
Hae
mon
chus
con
tortu
s;
H. p
lace
i C
oope
ria s
pp.
Mol
inei
dae
Nem
atod
irus
spp.
St
rong
ylid
aeO
esop
hago
stom
um r
adia
-tu
m; O
. ven
ulos
um;
O. c
olum
bian
um
Cha
berti
a ov
ina
Ancy
lost
omat
idae
Buno
stom
um
phle
boto
mum
-
Introduction to the Endoparasites 61
* Sev
eral
oth
er s
peci
es o
f Ost
erta
gia
exis
t and
may
cau
se o
r con
tribu
te to
dis
ease
. N
ot m
entio
ned
furth
er in
this
boo
k.
Dic
tyoc
aulid
aeD
icty
ocau
lus
lar
ia;
D. v
ivip
arus
Pr
otos
trong
ylid
aeM
uelle
rius
capi
llaris
Pr
otos
trong
ylus
spp
. Sp
irurid
aTh
elaz
iidae
Thel
azia
skr
jabi
ni; T
. gul
osa
Gon
gylo
nem
atid
aeG
ongy
lone
ma
pulc
hrum
; G
. ver
ruco
sum
O
ncho
cerc
idae
Seta
ria la
biat
opap
illos
a O
ncho
cerc
a gu
ttero
sa;
O. l
iena
lis
Fila
riida
eSt
epha
nol
aria
stil
esi
Aden
opho
rea
Enop
lida
Tric
hurid
aeTr
ichu
ris b
ovis
; T. o
vis;
T.
skr
jabi
ni
Cap
illar
iidae
Aonc
hoth
eca
bovi
s
-
62 Introduction to the Endoparasites Ta
ble
36
Cla
ssi
catio
n of
Nem
atod
es E
ncou
nter
ed in
Dog
s an
d C
ats
Clas
sO
rder
Fam
ily
Spec
ies
Sece
rnen
tea
Rhab
ditid
aSt
rong
yloi
dida
eSt
rong
yloi
des
ster
cora
lis
Stro
ngyl
ida
Ancy
lost
omat
idae
Ancy
lost
oma
cani
num
; A.
tuba
efor
me;
A. b
razi
liens
eU
ncin
aria
ste
noce
phal
aM
olin
eida
eO
llula
nus
tricu
spis
* An
gios
trong
ylid
aeAl
euro
stro
ngyl
us a
bstru
sus
Angi
ostro
ngyl
us s
pp.*
Fila
roid
idae
Fila
roid
es o
sler
i; F.
hirt
hi*
Cre
noso
mat
idae
Cre
noso
ma
vulp
is*
Asca
ridid
aTo
xoca
ridae
Toxo
cara
can
is; T
. mys
tax
Asca
ridiid
aeTo
xasc
aris
leon
ina
Bay
lisas
caris
pro
cyon
is
Spiru
rida
Spiro
cerc
idae
Spiro
cerc
a lu
pi
Phys
alop
terid
aePh
ysal
opte
ra s
pp.
Thel
aziid
aeTh
elaz
ia c
alifo
rnie
nsis
-
Introduction to the Endoparasites 63
* Not
men
tione
d fu
rther
in th
is b
ook.
Onc
hoce
rcid
aeD
irol
aria
imm
itis
Acan
thoc
heilo
nem
a re
cond
itium
Dra
cunc
ulid
aeD
racu
ncul
us in
sign
is
Aden
opho
rea
Dio
ctop
hym
ida
Dio
ctop
hym
a-tid
aeD
ioct
ophy
me
rena
le
Enop
lida
Tric
hurid
aeTr
ichu
ris v
ulpi
s; T
. cam
panu
la;
T. s
erra
ta
Cap
illar
iidae
Aonc
hoth
eca
puto
rii
Euco
leus
bh
mi;
Euco
leus
aer
ophi
lus
Pear
sone
ma
plic
a;
Pear
sone
ma
felis
cati
-
64 Introduction to the Endoparasites
Tab
le 3
7C
lass
ica
tion
of N
emat
odes
Enc
ount
ered
in P
oultr
y an
d O
ther
G
allin
aceo
us B
irds
Clas
sO
rder
Fam
ily
Spec
ies
Sece
rnen
tea
Rhab
ditid
aSt
rong
yloi
dida
eSt
rong
yloi
des
aviu
m
Stro
ngyl
ida
Syng
amid
aeSy
ngam
us tr
ache
a H
eter
akid
aeH
eter
akis
gal
linar
um
Asca
ridiid
aeAs
carid
ia g
alli
Aden
opho
rea
Enop
lida
Cap
illar
iidae
Euco
leus
ann
ulat
us
Euco
leus
con
tortu
s B
arus
capi
llaria
obs
igna
ta
-
mental times presented throughout the book areminimum times required under optimal conditions).
For most parasitic nematodes, the third-stage larva isthe infective stage (i.e., the stage that initiates infectionin the definitive host); infective larvae cannot feed andare usually ensheathedthe third-stage larvae do notcompletely shed the cuticular sheath of the second-stage larvae until some point after being ingested; thesheath provides protection against adverse environ-mental conditions; after the infective L3 sheds thesheath of the L2, they are referred to as parasitic L3.
Transmission may be direct (no intermediate hostrequired) or indirect (intermediate host required orparatenic host involved).
Development to adulthood may proceed normallyor, under certain circumstances, larvae may arrestdevelopment and remain quiescient until reacti-vated at a later time.
Adults infect a variety of organs; larval migration may ormay not occur depending on species and site of infection.
Acanthocephalans (Thorny-Headed Worms)Appearance and Morphology
Variable length, 6 mm to 30+ cm.
Proboscis is retractable into body; body covered withtegument; absorbs nutrients.
Introduction to the Endoparasites 65
-
Usually sexually dimorphic wi