Equine Ascarid Clinical Pathology

CLINICAL PATHOLOGY I – Lecture The Equine Ascarid: The horse has only one Parascaris equorum o Largest equine parasite: Up to 10” long o Direct life cycle o Prepatent period = 3 months o Primarily parasite of nursing and weaned foals < 1 year of age o...

CLINICAL PATHOLOGY I – Lecture The Equine Ascarid: The horse has only one Parascaris equorum o Largest equine parasite: Up to 10” long o Direct life cycle o Prepatent period = 3 months o Primarily parasite of nursing and weaned foals < 1 year of age o Adults live in small intestine o Occupy lots of space in bowel and can cause obstruction leading to rupture o Age-related immunity against P. equorum does develop P. equorum Life Cycle o Highly resistant, sticky eggs passed in feces o Ova become infective in ~ 10 days o Fecal-oral transmission: Infective ova ingested by next DH and hatch in small bowel o Larvae migrate through wall of small intestine and begin tracheal migration o Larvae migrate to liver via portal vein o Larvae then travel via circulation to lungs and cross into alveoli o Larvae crawl (or are coughed) up trachea, swallowed back to small bowel and, following mucosal migration, mature to adults o Prepatent period = 3 months Pathology o Migrating larvae cause tissue damage  Inflammatory tracts in liver  Inflammatory nodules in lungs o Lesions eventually heal, but reduction in functional capacity (especially lungs) at young age leaves mark Clinical Signs o Prepatent infestation (ascarid larvae): Foals infested at birth may show clinical signs at 4 to 6 weeks of age  Cough  Nasal discharge  “Verminous pneumonia” o Patent infestation (ascarid adults):  Diarrhea, flatulence  “Poor doer”: Unthrifty; rough hair coat; leathery skin; enlarged abdomen  Anorexia  Reduced weight gain or actual weight loss  Colic  Death following impaction and intestinal rupture resulting in fatal peritonitis 12/3/2024 1 Diagnosis o Prepatent infestation  “Coughing foal with nasal discharge”  Tracheal wash to recover migrating larvae  Empirical treatment with anthelmintic and observe for improvement in clinical signs  Diagnosis sometimes made at necropsy o Patent infestation  Fecal float with characteristic ova  Ova sometimes lose thick protective shell during collection and/or processing for fecal flotation o Thick shelled (larger) o Smooth shelled (smaller)  These are both Parascaris ova Treatment o Many effective deworming agents available  Ivermectin, moxidectin (both effective against P. equorum but shouldn’t be used in foals < 6 months of age)  Fenbendazole, oxibendazole  Pyrantel (daily in feed after weaning) o Begin treatment at 8 weeks of age; treat at two-month intervals for first year of life Treatment Warning o Administration of anthelmintics that paralyze ascarids (e.g., piperazine, ivermectin, and pyrantel) to foal with heavy infestation of P. equorum adults can cause impaction and/or complete obstruction o Treat during prepatent period OR o Treat with lower dose of BZDs and repeat in 10 to 14 days Prevention is Difficult o Female worms are prolific egg layers -- infested foals may pass millions of eggs daily in feces o Thick-shelled ova resistant to freezing and drying, can survive for long periods (years) o Chemicals do not kill ova o Sticky outer layer ensures eggs present almost everywhere in foal's environment  Bedding - Mangers  Stall floor and walls - Water buckets  Dam’s udder + teats - Pasture o Foals are coprophagic -- seeding cecum and colon with bacteria and protozoa necessary for fermentation o Chemical disinfectants have no appreciable effect on P. equorum ova o High-pressure steam-cleaning will kill ova 12/3/2024 2  o Before foaling  Steam-clean foaling stall  Wash mare’s udder and teats immediately before parturition  Deworm mare day she foals Age-Related Immunity o Infestation rates in foals decline significantly by six months due to  Age-related resistance  Potent immune response o By 12 months of age, patent infestations in horses relatively uncommon o Immunity usually lasts throughout adult lives 12/3/2024 3