Equine GI Parasites

Equine GI Parasites

1. Strongylidae family

   • Cyathostominae
     • 50spp, 10 are common, including small red worm
     • Highly prevalent, all horses have a burden because L3 migrates away from faecal pat
     • Direct non-migratory lifecyle, PPP 6-12w,
       • ALD: L3 undergo ALD for moths to years in intestinal lining. L4 and adults in intestine control emergence with negative feedback.
         • Tx: ineffective against ALD
       • Cyathostominosis
         • Dx: faecal larvae
         • Tx protocol
           • Ivermectin (kills adults) D1, 16, 31 Fenbendazole (known resistance) D1-5, 16-20, 31-35. Prednisolone (stop IBS & PLE) q24 D1-20, q48 D21-40 Codeine Phosphate (Diarrhoea tx) D1-20 tapering dose
         • Resumption of larval development
           • After AH dose or in late winter/spring = PLE, rapid WL, +/- D+, prepucial oedema
   • Strongylus species
     • 6 strongylus species, including the Large Red Worm
       • Strongylus vulgaris is most important
       • Direct migratory lifecycle. PPP 6-10m. Sheathed L3 ingested and exsheath in SI, penetrate SI mucosa and arteries and develop to L4, migrate through the arteries to the Cr mesenteric artery. L5 returns to the intestine wall, adults rupture out of caecum and colon mucosa. Plug feeders so cause minimal pathology from feeidng. Lay eggs into faeces which hatch and mouth to L3 >8'C
         • Pathology: migration through the SI causes infarction which can be massive and widespread
           • non-strangulating intestinal infarction = colic
             • Prevention is key: All stages in the host are sensitive to BZ, pyrantel and ivermectin

2. Parascarid equorum

   • Infective stage is the larvated egg which survives on pasture year to year. Direct migratory lifecycle: Intestine, liver, lung, SI. PPP 3m.
     • Good de-worming protocol prevents
       • 5d Fenbendazole (adulticide only)
   • Disease of young horses - immunity developed by 18m
     • Ill thrift
       • FWEC is diagnostic
     • Colic (impaction of SI shortly after AH dose)
     • Respiratory signs (very rare)

3. Tapeworms

   • Anoplocephala perforlitata and others
   • Indirect life cycle, ImH is the orbatid mite. PPP 6-10m.
     • Adult at ileo-caecal junction is asc with colic
     • Dx: serology Ab ELISA
     • Tx: Praziquantel or double dose pyrantel

4. Others

   • Bots
     • Gasterophilius spp
     • Oestrid fly deposits eggs/larvae on coat, eggs ingested via grooming, overwinter in GIT, pass in host faeces in spring, adult flies emerge 1-2m later
   • Strongyloides westeri
     • Parasite of foals' SI - absoloute immunity by 5m
       • Most are asymptomatic, heavy burden may present lethargic, anorexic, D+
       • Don't prophylactically treat
   • Pinworm
     • Oxyuris equi
       • Adults sit in descending colon and rectum, cause rectal pruritus, may cause some mucosal inflammation during migratory phase but generally non-pathogenic

5. Reccomended Treatment and control

   • Cyathostomins, Tapeworn and Ascardi control most important
     • Strongyles
       • FEWC monthly, anything >200epg gets dosed
     • Tapeworm
       • Serology and targeted dosing, or dose once annually (winter often)
     • Ascarids
       • dose around 2-3m old if control on stud is needed
   • Non-AH reliant
     • Pasture hygiene is unproven
     • Co-grazing with sheep is effective control
     • Monitor resistance
       • FWE reduction test
         • FWEC, dose, FWEC 10-14d later and calculate % change
           • < 90% reduction = resistance

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