Tabanids: Horse Flies and Deer Flies

Announcements

Reading: Chaps 15, 18, 19.

Speaking Today: Mark Goodman, Charity Selbrede

Speaking Next Tuesday: Lauren Torbett, Micah Pepper

Quiz Review• Question 1. Any 2 out of 3.

– a. Black Fly Pupae (Fig. 13.2, p.190)– b. Adult Fly– c. Habitat: Fast/Free flowing water; Location: Anywhere

(Except Arctic/Ant)

• Question 2, 3, 4, 5: A, A, B, D

• Question 6. Grading 3 out of 4.– a. Sporozoans– b. Malaria– c. Anopheles spp. mosquitoes– d. P. falciparum most dangerous, different time intervals

were the most common answers.

Class Scores on Quiz 2

0

1

2

3

4

5

6

7

8

<6 6 7 8 9 10

Points Out of 10 Possible

Nu

mb

er

of

Stu

de

nts

Tabanids

• 4300 spp in 133 genera • 3 subfamilies (one of which is not common)

– Tabaninae – Horse Flies, livestock pests but do not often bite humans

– Chrysopinae – Deer Flies, livestock AND people biters

Blood Feeding

• Only females take blood• Anautogenous species usually need a single

large blood meal– Anautogenous – need a blood meal to make eggs– Autogenous – can make eggs without a blood meal

using reserves left over from larval stage– Facultatively Autogenous – can make eggs without

a blood meal but, with a blood meal, typically make more eggs with higher viability

• Attracted to host by a variety of visual, chemical, and thermal cues

Tabanids are Classic Telmophages

• Mouthparts use a scissor action to cut skin

• Saliva produces anticoagulant & vasodialator

• Lap up the pool of blood• Wound often continues

to bleed after the fly has fed (attracting other insects)

• Painful bite means that the flies are often selective on the body part that they target.

Medical/Veterinary Significance

• Nuisance• Allergy from saliva• Secondary Infections• Transmit a variety of

pathogens to livestock and deer– Most of the serious

problems are in the tropics of Africa and S. America

• Two significant human diseases

Tularemia

• AKA “deer fly fever” or “rabbit fever”

• Etiological agent is the bacterium, Francisella tularensis

• Ticks are more important vectors (of this and a couple of other diseases)

• Can also be contracted by contact with blood of infected rabbits

• Causes a distinctive septicemic ulcer requiring antibiotics.

Especially bad in Arkansas and Missouri

Tularemia in humans has declined • Decline in wild rabbit hunting,

• Greater use of insect repellents

• Greater public awareness

• Note: many anecdotal reports of increasing rabbit populations in US suburbs.

Loiasis

• Most important tabanid-transmitted disease in humans

• Etiological agent are filarial nematodes in the genus Loa, esp. L. loa.

• Transmitted by deer flies in the genus Chrysops in Western & Central Africa.

• In some areas > 90% of people are infected.

Transmission Cycle

• Humans are definitive hosts• Flies ingest microfilarae• Microfilarae penetrate fly gut wall, migrate to fat

tissue, grow to 3rd instar• Third instars migrate to fly head/mouthparts• When fly feeds, larvae exit & burrow into human.• Live beneath skin, esp. in the thorax and scalp

particularly in eyes.• For this reason, human loiasis also called “eye

worms”

Eye Worms

• Loa loa extraction from human eye

• Another extraction

Interaction with Ivermectin & Onchocerciasis

• Patients treated with ivermectin for onchocerciasis who also have loa loa sometimes develop encephalopathy (generic brain disorder)

• Mostly men from Cameroon• Most Serious Adverse Effect (SAE) of Ivermectin treatment• Includes an unknown but suspected involvement with malaria• Involves filarae migrating from subcutaneous tissue to brain tissue.• Recent mass treatment of 800,000 people resulted in 65 of these SAE’s

Tse Tse Flies

• Family Glossinidae• One genus, Glossina, with

23 spp.• All in subsaharan Africa• Species are grouped by

generic habitat– palpalis group of 5 riverine

spp.– fusca group of 5 forest spp.– morsitans group of 5

savanna spp.• Vector of African

trypanosomiasis, “Sleeping Sickness”

Tse Tse Fly Biology

• Both sexes blood feed• Strong host preferences by species

– Humans are not preferred hosts of any species

• Female usually only mates one time.• Populations are often scattered at low

densities over wide areas.• Flies congregate near hosts as a way of

mate location

Biggest Med/Vet Issue is Trypanosmiasis

• Trypanosoma.– 6 spp. cause sleeping sickness in

wild/domesitic animals.– One of these, T. brucei, also infects humans– It has two subspecies, each causing a

different disease• T. b. gambiense – West African Sleeping Sickness• T. b. rhodesiense – East African Sleeping

Sickness

West African Sleeping Sickness• Initially a skin lesion with

swelling• Winterbottom’s sign – swelling

of cervical lymph nodes• Eventually parasite enters CNS• CNS involvement often results

in wasting condition.• Untreated patients lapse into

stupor, convulsions, death.

East African Sleeping Sickness

• Acute onset of fever, headache dizzyness• Instead of lymphatic disease, this is a circulatory

disease• Early heart problems (tachycardia [rapid beating]

& arrythmia [abnormal heart rate])• Biochemical interaction between immune

response and trypanosomes kill blood cells, damage brain tissue (other organs too)

• Trypanosomes migrate to the CNS• From there, similar to WASS but faster

Like most arthropod borne pathogens, vector control is important• Flies are sparse in most of their range, location

of hotspots is known.• Eradication technology is available but not the

resources.• Instead, main plan is to:

– reduce fly populations via insecticides, habitat manipulation, etc.

– reduce trypanosome burden via trypanotolerant livestock

– reduce human impact pharmacologically