Equine Parasites Equine Parasites

General ConsiderationsGeneral Considerations

Parasites are most successfully Parasites are most successfully prevented through a combination of prevented through a combination of management and therapeutic strategiesmanagement and therapeutic strategies

ManagementManagement Decrease parasite burden in Decrease parasite burden in

environmentenvironment TherapeuticTherapeutic Deworming with proper product at Deworming with proper product at

proper intervalsproper intervals

Parasite PreventionParasite Prevention

Adequate pasture acreageAdequate pasture acreage Compost manureCompost manure CleanlinessCleanliness Pasture rotationPasture rotation Mixed grazing (cattle and horses)Mixed grazing (cattle and horses)

Pasture RotationPasture Rotation

Infective larvae on pasture decreases Infective larvae on pasture decreases greatly over the winter and also in hot, greatly over the winter and also in hot, humid days of summerhumid days of summer

Move horses from old, infested pastures Move horses from old, infested pastures to ones that have minimal numbers of to ones that have minimal numbers of infective larvaeinfective larvae

Deworm prior to movingDeworm prior to moving Foals and young horses should go to Foals and young horses should go to

cleanest available pasturescleanest available pastures

Internal parasitesInternal parasites

The amount of clinical disease a The amount of clinical disease a horse will show depends on three horse will show depends on three factors:factors:

1.1. Type of parasite involvedType of parasite involved

2.2. Number of parasites involvedNumber of parasites involved

3.3. Host defenses. Young and Host defenses. Young and debilitated animals more debilitated animals more susceptiblesusceptible

Life Cycle of Parasites Life Cycle of Parasites

EggsEggs Larvae (immature worms)Larvae (immature worms) Adults (mature worms) Adults (mature worms)

Life cycle of the parasite Life cycle of the parasite Eggs or larvae are Eggs or larvae are

deposited on the ground in deposited on the ground in the manure of infected the manure of infected horsehorse

The eggs and larvae The eggs and larvae develop in the environment develop in the environment and are swallowed while and are swallowed while the horse is grazingthe horse is grazing

Larvae mature in the Larvae mature in the horse’s digestive tract horse’s digestive tract where most of them where most of them become egg laying adults. become egg laying adults.

Internal parasites – Internal parasites – CommonCommon

signssigns Poor growthPoor growth Weight lossWeight loss Decreased feed Decreased feed

efficiencyefficiency ColicColic DiarrheaDiarrhea PneumoniaPneumonia DeathDeath

Dull hair coat Dull hair coat

Clinical sign – colic Clinical sign – colic

Poor performance Poor performance

Important Parasites in Important Parasites in the horsethe horse

Large strongyle (Large strongyle (Stongylus vulgaris, Stongylus vulgaris, S.edentatus, S.equinusS.edentatus, S.equinus))

Small strongyle (Cyathostemes)Small strongyle (Cyathostemes) Round worm (Ascarids)Round worm (Ascarids) Bots (Bots (Gastrophilus sppGastrophilus spp)) Pin worms (Pin worms (Oxyuris equiOxyuris equi)) Tapeworms (Tapeworms (AnoplochephalaAnoplochephala)) Threadworm (Threadworm (StrongyloidesStrongyloides))

Large StrongyleLarge Strongyle Strongylus vulgarisStrongylus vulgaris

Blood worm- bloodsucking of the large Blood worm- bloodsucking of the large instestineinstestine

Most dangerous parasite of horsesMost dangerous parasite of horses Causes thromboembolic colic, various Causes thromboembolic colic, various

degrees of anemia.degrees of anemia. Direct life cycleDirect life cycle Larvae live in artery supplying blood to Larvae live in artery supplying blood to

the intestines. Blood clots form which the intestines. Blood clots form which block blood supply to the intestineblock blood supply to the intestine

First stage is the egg in feces or soil, molts First stage is the egg in feces or soil, molts to 2to 2ndnd stage in feces or soil. 3 stage in feces or soil. 3rdrd stage stage becomes “sheathed” or sticks to walls, becomes “sheathed” or sticks to walls, buckets, etc.buckets, etc.

When ingested by the horse the When ingested by the horse the infectiveinfective 33rdrd stage stage larvae of larvae of S.vulgarisS.vulgaris cast off there cast off there sheath in the lumen of the s. intestine and sheath in the lumen of the s. intestine and enter the wall of the cecum and ventral enter the wall of the cecum and ventral colon. They curl up under the mucous colon. They curl up under the mucous membrane and prepare to molt. After 8 membrane and prepare to molt. After 8 days the molt is complete and become a 4days the molt is complete and become a 4thth stage larva and resume migration. stage larva and resume migration.

44thth stage penetrate nearby small arterioles and stage penetrate nearby small arterioles and wanders to the cranial mesenteric artery, wanders to the cranial mesenteric artery, which supplies blood to the instestine. (this which supplies blood to the instestine. (this leaves a path of inflammation, which can lead leaves a path of inflammation, which can lead to thrombosis or occlude the vessel) After 2-4 to thrombosis or occlude the vessel) After 2-4 months they enter the surrounding tissue of months they enter the surrounding tissue of the intestinal wall and a final molt takes place the intestinal wall and a final molt takes place and the immature adults (5and the immature adults (5thth stage) enter the stage) enter the lumen of the cecum and ventral colon , mature lumen of the cecum and ventral colon , mature and reproduce 6 months after original and reproduce 6 months after original ingestioningestion

Collateral circulationCollateral circulation

Life Cycle Life Cycle

Adult large strongyle Adult large strongyle

Strongylus vulgaris,adults Strongylus vulgaris,adults in equine intestine in equine intestine

“bloodworms”“bloodworms”

After deworming “red After deworming “red worms”worms”

This verminous arteritis This verminous arteritis lesion is from the lesion is from the cranial mesenteric cranial mesenteric artery of a weanling artery of a weanling Quarter Horse colt.  Quarter Horse colt.  Verminous arteritis is Verminous arteritis is caused by the migration caused by the migration of larvae of Strongylus of larvae of Strongylus vulgaris through the vulgaris through the blood vessels.  It was blood vessels.  It was once a common cause of once a common cause of colic and death in colic and death in domestic horses.  domestic horses. 

S.edentatus, S. equinusS.edentatus, S. equinus

2 times as large as adults 2 times as large as adults The 3The 3rdrd stage of stage of S. edentatus S. edentatus migrate to the migrate to the

liver, become encapsulated and molt to the liver, become encapsulated and molt to the 44thth stage in approx. 2 weeks. After molting stage in approx. 2 weeks. After molting the larvae wander aimlessly in the liver for the larvae wander aimlessly in the liver for 2 months, leave the liver by ligaments that 2 months, leave the liver by ligaments that hold the liver in position, wander for hold the liver in position, wander for months in the connective tissues, and 11 months in the connective tissues, and 11 months (PPP) after ingestion can be found months (PPP) after ingestion can be found in the lining of the cecum and colon.in the lining of the cecum and colon.

33rdrd stage stage S.equinusS.equinus encyst and undergo encyst and undergo molt in the wall of the large intestine. molt in the wall of the large intestine. After molting they bore into the right After molting they bore into the right half of the liver which lies in contact half of the liver which lies in contact with this portion of the large intestine. with this portion of the large intestine. They stay for 6-7 weeks, enter the They stay for 6-7 weeks, enter the pancreas and abdominal cavity where pancreas and abdominal cavity where the complete their development to the complete their development to adults. Reenter the lumen of the large adults. Reenter the lumen of the large intestine and mate. (9mo. PPP) intestine and mate. (9mo. PPP)

Large and small Large and small strongyle strongyle

DiagnosisDiagnosis

Diagnosis of mixed strongyle Diagnosis of mixed strongyle infection is based on demonstration infection is based on demonstration of eggs in the feces. Specific of eggs in the feces. Specific diagnosis can be made by identifying diagnosis can be made by identifying the infective larvae after fecalthe infective larvae after fecal

Large Strongyles Large Strongyles

Treat every 6 months Treat every 6 months Use Ivermectin or monoxidecin Use Ivermectin or monoxidecin

Small Small Strongyle- Strongyle- CyathostominaeCyathostominae

Numerous species of Numerous species of strongyles (40)strongyles (40)

Direct Life cycleDirect Life cycle Larvae life in gut wall of large Larvae life in gut wall of large

intestine- therefore not as intestine- therefore not as pathogenic as large stongylepathogenic as large stongyle

Cause damage to gut wall Cause damage to gut wall resulting in G.I. upset, and resulting in G.I. upset, and severe diarrhea. severe diarrhea.

Internal parasites of highest Internal parasites of highest concern- encysted stage is concern- encysted stage is not affected by dewormers not affected by dewormers

Very short life cycle 4 to 6 Very short life cycle 4 to 6 weeks weeks

Life Cycle Life Cycle

Symptoms Symptoms ColicColic DiarrheaDiarrhea Ill-thrift, loss of body conditionIll-thrift, loss of body condition Subclinical diseases is more common and Subclinical diseases is more common and

may result in greater economic losses may result in greater economic losses

Diagnosis of StrongylesDiagnosis of StrongylesFecal flotation- small andFecal flotation- small and

large stongyles look similar on float. large stongyles look similar on float.

Assume the worst and treat for largeAssume the worst and treat for largeNecropsyNecropsy

Encysted cyathostome larvae in the Encysted cyathostome larvae in the large colon of a horse. large colon of a horse.

Treatment Treatment Many products available – nearly all horse Many products available – nearly all horse

wormers are effective against adults in wormers are effective against adults in the GI tractthe GI tract

Ivermectin, mixodectin, and fenbendazole Ivermectin, mixodectin, and fenbendazole effective against migrating larvaeeffective against migrating larvae

Check fecal samples for eggs to gauge Check fecal samples for eggs to gauge success of worming programsuccess of worming program

Control of strongylesControl of strongyles

Use effective wormers routinelyUse effective wormers routinely Avoid overgrazing pastureAvoid overgrazing pasture Use clean pastures for young Use clean pastures for young

animalsanimals Pile and compost manurePile and compost manure

*No public health significance*No public health significance

PinwormsPinwormsOxyuris equiOxyuris equi

Adult pinworms lay eggs around the anusAdult pinworms lay eggs around the anus Direct lifecycleDirect lifecycle Eggs cause irritation and horses will rub Eggs cause irritation and horses will rub

their tails against objectstheir tails against objects Bare patches around the tail and Bare patches around the tail and

perineum- perineum- pruritus anipruritus ani Vague signs of abdominal discomfort if Vague signs of abdominal discomfort if

anyany Controlled by most wormersControlled by most wormers

Life Cycle Life Cycle

PinwormsPinworms

Diagnosis of Pin WormsDiagnosis of Pin Worms Egg masses in Egg masses in

perineal regionperineal region Tail rubbingTail rubbing Eggs in feces Eggs in feces

(rare)(rare) Adults in fecesAdults in feces

Pinworms usually are the cause of the Pinworms usually are the cause of the irritation that leads to tail rubbing. irritation that leads to tail rubbing. Adult females deposit adhesive egg Adult females deposit adhesive egg masses on anal and perianal skin. masses on anal and perianal skin. Note the broken hair at the base of Note the broken hair at the base of the tail.the tail.

Adults in fecesAdults in feces

Control of Pin WormsControl of Pin Worms

Thorough cleaning of stallsThorough cleaning of stalls Fresh food and waterFresh food and water

Stomach botsStomach botsGastrophilus sspGastrophilus ssp

Insects – the adult is a fly, the larvae Insects – the adult is a fly, the larvae live in the horse’s stomachlive in the horse’s stomach

Flies lay eggs on hair, they hatch and Flies lay eggs on hair, they hatch and penetrate into the mouth tissue, then penetrate into the mouth tissue, then migrate to stomachmigrate to stomach

May cause stomach irritation and colicMay cause stomach irritation and colic

G. nasalis, G. hemorrhoidalis, G. G. nasalis, G. hemorrhoidalis, G. intestinalisintestinalis

Life Cycle Life Cycle

Bot fly and eggBot fly and egg

Bot fly larvaeBot fly larvae Migrate thru the Migrate thru the

tongue and tongue and esophagus after they esophagus after they are ingested, and are ingested, and attach themselves to attach themselves to the lining of the the lining of the stomach, where they stomach, where they stay for up to 11 stay for up to 11 months. In large months. In large numbers, they numbers, they contribute to gastric contribute to gastric (stomach) ulcers and (stomach) ulcers and occasionally rupture occasionally rupture of the stomach. of the stomach.

gross lesion with adult gross lesion with adult worms, equine stomach worms, equine stomach

Mutual grooming leads to the Mutual grooming leads to the ingestioningestionof bot eggs by horsesof bot eggs by horses

Diagnosis of BotsDiagnosis of Bots

See eggs on See eggs on hair and manehair and mane

Endoscopy of Endoscopy of stomachstomach

NecropsyNecropsy Knowing flies Knowing flies

are in areaare in area

Treatment of BotsTreatment of Bots Because flies are insects, only Because flies are insects, only

wormers that are effective against wormers that are effective against insects will kill botsinsects will kill bots

Ivermectin and moxidectin are Ivermectin and moxidectin are effectiveeffective

Nits can be removed from hair Nits can be removed from hair before they hatchbefore they hatch

Nit removal combs, pumice stonesNit removal combs, pumice stones Warm water with insecticide addedWarm water with insecticide added

Public health significancePublic health significance

Flies can lay eggs on human hairFlies can lay eggs on human hair Larvae will hatch and burrow into Larvae will hatch and burrow into

skinskin

The stomach worms The stomach worms Habronema muscae H Habronema muscae H

microstoma , and Draschia microstoma , and Draschia megastomamegastoma

The adults are 6-25 mm in size. The adults are 6-25 mm in size. Draschia are found in tumor-like Draschia are found in tumor-like swellings in the stomach wall. swellings in the stomach wall.

The eggs or larvae are ingested by The eggs or larvae are ingested by larvae of house or stable flies, which larvae of house or stable flies, which serve as intermediate hosts. Horses are serve as intermediate hosts. Horses are infected by ingesting flies that contain infected by ingesting flies that contain infective larvae or by free larvae that infective larvae or by free larvae that emerge from flies as they feed around emerge from flies as they feed around the lipsthe lips

HabronemaHabronema

If the larvae which are in the mouthparts of If the larvae which are in the mouthparts of the immediate host are deposited in the open the immediate host are deposited in the open skin well the fly feeds it can cause skin well the fly feeds it can cause summer summer soressores. .

Summer sores Summer sores are ulcerated irritations. are ulcerated irritations. These lesions can cause soreness and These lesions can cause soreness and itchiness and become covered in a reddish-itchiness and become covered in a reddish-yellow tissueyellow tissue

If the worms get deposited into the eye or If the worms get deposited into the eye or the area around the eye it can cause a the area around the eye it can cause a persistent case of conjunctivitis.persistent case of conjunctivitis.

CycleCycle

LesionsLesions

Ascarids - RoundwormsAscarids - Roundworms Parascaris equorumParascaris equorum Most common in foals/young horses –can cause Most common in foals/young horses –can cause

impactation and colicimpactation and colic Interfere with digestion and absorption of Interfere with digestion and absorption of

nutrients, notably proteinnutrients, notably protein Cause telescoping of intestine in foalsCause telescoping of intestine in foals Direct life cycleDirect life cycle Larvae migrate through lungs where they can Larvae migrate through lungs where they can

cause pneumoniacause pneumonia Build up in large numbers in the anterior part of Build up in large numbers in the anterior part of

the small intestinethe small intestine

Parascaris equoru mParascaris equoru m1 celled egg in feces (1-2 weeks)1 celled egg in feces (1-2 weeks)

Infective eggs are swallowed, they hatch and Infective eggs are swallowed, they hatch and liberate liberate infective 2infective 2ndnd stage stage larvae, which burrow larvae, which burrow into the wall of the small intestine and are carried into the wall of the small intestine and are carried to the liver by the portal vein. After migrating to the liver by the portal vein. After migrating through the liver tissue, they enter the hepatic through the liver tissue, they enter the hepatic vein and are carried by the posterior vena cava to vein and are carried by the posterior vena cava to the lungs, where they break the into the alveoli, the lungs, where they break the into the alveoli, molt and are coughed up and swallowed, molt and are coughed up and swallowed, returning to the small intestine to mature. returning to the small intestine to mature. (3months) (3months)

Eggs have proteinaceous layer and is sticky. Eggs Eggs have proteinaceous layer and is sticky. Eggs adhere to stall walls, mangers, buckets, etc. adhere to stall walls, mangers, buckets, etc.

Life Cycle Life Cycle

Ascarid Ascarid

Can grow up to 12 inches in length within Can grow up to 12 inches in length within 4 weeks and block the small intestines.4 weeks and block the small intestines.

Ascarids – Clinical SignsAscarids – Clinical Signs

Impaction colic – deathImpaction colic – death PneumoniaPneumonia Pot bellyPot belly Unthrifty appearanceUnthrifty appearance Poor hair coatPoor hair coat

Spaghetti for dinner?? Spaghetti for dinner??

Ascarid impactation and Ascarid impactation and rupturerupture

Parascaris equorum Parascaris equorum

Ascarid in the bile system Ascarid in the bile system of the liver of the liver

Diagnosis of ascaridsDiagnosis of ascarids

Clinical signsClinical signs Fecal flotationFecal flotation NecropsyNecropsy

Control of AscaridsControl of Ascarids

Good sanitationGood sanitation Eggs live in environment for many Eggs live in environment for many

yearsyears Avoid putting foals in same pastures Avoid putting foals in same pastures

year after yearyear after year Regular worming of foals and young Regular worming of foals and young

stockstock

Treatment of AscaridsTreatment of Ascarids

Most common wormers are effective Most common wormers are effective against ascarids (Safeguard, against ascarids (Safeguard, Panacur, Strongid, Ivermectin) Panacur, Strongid, Ivermectin)

If a foal has a very heavy infection it If a foal has a very heavy infection it should be wormed with less effective should be wormed with less effective products to prevent impactionproducts to prevent impaction

TapewormsTapeworms

Three species of tapeworms are found Three species of tapeworms are found in horses: in horses: AnoplocephalaAnoplocephala magnamagna , , AA perfoliataperfoliata , and , and ParanoplocephalaParanoplocephala mamillanamamillana

Found mostly in the cecum but may Found mostly in the cecum but may also be in the small intestine. also be in the small intestine.

Young and older horses more Young and older horses more susceptible -mitesusceptible -mite

Difficult to detect on fecal exam. Difficult to detect on fecal exam.

Tape worms Tape worms ((Anaplocephala)Anaplocephala)

Cause colicCause colic Live at ileo-cecal valve Live at ileo-cecal valve Disrupt motilityDisrupt motility Use prazinquantel Use prazinquantel

Difucult to detect the eggs on fecal Difucult to detect the eggs on fecal sample sample

Infection of A. perfoliata with Infection of A. perfoliata with intussusception of the ileum into the intussusception of the ileum into the

cecum.cecum.

A cluster of tapeworm segments at A cluster of tapeworm segments at the ileocecal valve are of the cecum the ileocecal valve are of the cecum

of a naturally infected horse.of a naturally infected horse.

Thread wormsThread wormsIntestinal ThreadwormIntestinal Threadworm

Strongyloides westeri –Strongyloides westeri – (strongyle-like) (strongyle-like) Life cycle as short at 2 weeksLife cycle as short at 2 weeks Infects young foals (2 weeks-6 months)Infects young foals (2 weeks-6 months) Larvae passed in mare’s milk to foalsLarvae passed in mare’s milk to foals May cause diarrhea in young foalsMay cause diarrhea in young foals Immunity quickly developed Immunity quickly developed DOES NOT cause foal heat diarrheaDOES NOT cause foal heat diarrhea Strongyloides is zoonotic, cutaneous Strongyloides is zoonotic, cutaneous

larva migraines, but not this specieslarva migraines, but not this species

Thread wormsThread worms

Can be free living in the Can be free living in the soil soil

Cutaneous larva migransCutaneous larva migrans

Larva can penetrate foal’s skin to Larva can penetrate foal’s skin to cause infectioncause infection

May species penetrate human skin May species penetrate human skin and cause problems in people as and cause problems in people as wellwell

Diagnosis of StrongyloidesDiagnosis of Strongyloides

Fecal exam for larvaeFecal exam for larvae Fecal cultureFecal culture VERY rarely may see eggsVERY rarely may see eggs

Stronglyoides eggStronglyoides egg(larvae moving)(larvae moving)

Treatment of StrongyloidesTreatment of Strongyloides

Worm mare prior to foaling to Worm mare prior to foaling to prevent larval migration to udderprevent larval migration to udder

Worm foals at 4 weeks of ageWorm foals at 4 weeks of age

Control of StrongyloidesControl of Strongyloides

SanitationSanitation Keep stall dry to kill larvaeKeep stall dry to kill larvae

Diagnosis of internal Diagnosis of internal parasites parasites

Fecal egg counts can be very helpfulFecal egg counts can be very helpful

negative fecal does not always mean no negative fecal does not always mean no parasitesparasites

Monitor multiple horses on the farm at the Monitor multiple horses on the farm at the same timesame time

Some parasites are difficult to diagnose – Some parasites are difficult to diagnose – tapewormstapeworms

Smear, float, centrifuge, and Baermann Smear, float, centrifuge, and Baermann apparatusapparatus

Baermann apparatusBaermann apparatus

Lung wormsLung worms

DewormersDewormers

None are 100% effectiveNone are 100% effective 2 month interval (6 times a year) *think life 2 month interval (6 times a year) *think life

cycles*cycles* Use a broad spectrum product as basis for Use a broad spectrum product as basis for

control (ivermectin, moxidectin)control (ivermectin, moxidectin) Be sure to treat for tapeworms 1-2 time per Be sure to treat for tapeworms 1-2 time per

yearyear Avoid creating resistance to anthelminticsAvoid creating resistance to anthelmintics

*Double dose strongid*Double dose strongid

*Product containing prazinquantel *Product containing prazinquantel

Dewormers Dewormers

Avermectins Avermectins Ivermectin (Eqvalan, Zimectin, Ivermectin (Eqvalan, Zimectin, EquimectrinEquimectrinMoxidectin (Quest)Moxidectin (Quest)

TetrahydropyrimidinesTetrahydropyrimidinesPyrantal (Strongid, Rotation0Pyrantal (Strongid, Rotation0

BenzimidazolesBenzimidazolesFebendazole (Panacur, Safeguard)Febendazole (Panacur, Safeguard)

PrazinquantelPrazinquantel

Parasite controlParasite control Manure removal at least Manure removal at least

2x/week2x/week Spread manure in hot Spread manure in hot

weather away from weather away from fields where horses are fields where horses are grazing grazing

Rotate Pasture- limit Rotate Pasture- limit overgrazing (different overgrazing (different species)species)

Group horses by ageGroup horses by age Use feeder for hay and Use feeder for hay and

graingrain Remove bot eggs from Remove bot eggs from

hair hair Deworm new arrivalsDeworm new arrivals

Questions ??Questions ?? CTVT pages 473-475, 488-CTVT pages 473-475, 488-

504504 LACP pages 329-330LACP pages 329-330