Parasites by Host - Horse PDF

PARASITES BY HOST: HORSE  BY THE END OF THIS PRESENTATION, YOU SHOULD BE ABLE TO: Provide a differential list of parasites that cause the clinical signs reported in the host Generate a diagnostic plan to rule in or out parasites on the differential list, and what the...

PARASITES BY HOST: HORSE  BY THE END OF THIS PRESENTATION, YOU SHOULD BE ABLE TO: Provide a differential list of parasites that cause the clinical signs reported in the host Generate a diagnostic plan to rule in or out parasites on the differential list, and what the expected findings would be for each test Design a treatment plan depending on the parasite affecting the host Inform owners regarding methods of prevention of future infections by these parasites MY HORSE HAS SKIN LESIONS Arthropods > Insecta > Diptera (flies) > Nematocera > Ceratopogonidae (midges) CERATOPOGONIDAE (MIDGES) Tiny ( Secernetea > Spirurida > Spirurina > Habronema HABRONEMATOIDEA Live as adults in stomach of horses, near margo plicatus Larvae or eggs passed in feces, ingested by muscid maggots and develop to L3 L3 deposited on muzzle by muscid flies, and are swallowed to complete life cycle Disease: Larvae deposited on wounds or mucous membranes cause granulomas (cutaneous habronemiasis, summer sores) Treatment: Ivermectin, moxidectin, surgical excision Nematoda > Secernetea > Oxyurida (pinworms) OXYURIDA (PINWORMS) Nematodes with long, tapering tails Esophagus with bulb (rhabditiform looking) Highly host-specific Gravid females exit rectum and deposit eggs to perianal skin Eggs develop to infective stage in 4-5 days and contaminate environment Disease: Pruritus ani, tail rubbing (“rat tail”) Diagnosis: Scotch tape test or fecal flotation Eggs have a polar plug and are asymmetrically flattened Treatment: Pyrantel pamoate, ivermectin, fenbendazole MY HORSE HAS COLIC/DIARRHEA  ACTIVE LEARNING ACTIVITY List some causes of colic in horses, and what tests you could run to rule in or out your differentials. Arthropods > Insecta > Trichoptera (caddisflies) TRICHOPTERA (CADDISFLIES) Potomac horse fever: Caused by Neorickettsia risticii Acquired by horses through ingestion of caddisflies in drinking water Acute enterocolitis Mild colic Fever Diarrhea Abortion in pregnant mares Can lead to laminitis Treatment: Oxytetracycline Platyhelminths > Cestodes > Cyclophyllidea (terrestrial tapeworms) > Anoplocephala ANOPLOCEPHALA Anoplocephala perfoliata: Live as adults in cecum and ileum of horses Definitive host infected when ingesting cysticercoid in oribatid mites during grazing Disease: Associated with ulceration and ileal inflammation Can predispose to intussusception near ileocecal valve Diagnosis: Eggs difficult to detect in feces ELISA test for IgG available Treatment: Pyrantel pamoate, praziquantel Nematoda > Secernentea > Strongylida (bursates) > Strongyloidea > Strongylus STRONGYLUS Live as adults in large intestine of horses mostly Strongylus vulgaris: Fourth stage larvae enter blood vessel walls and migrate to cranial mesenteric arteries Migration cause arteritis, thrombosis, and embolism of cranial mesenteric arteries Bowel wall infarction is frequent and fatal Diagnosis: Strongyle-type eggs in fecal flotation Indistinguishable from small strongyle (cyathostome) eggs Eggs may not be passed when clinical signs develop Treatment: Benzimidazoles, macrocyclic lactones, pyrantel pamoate Nematoda > Secernentea > Strongylida (bursates) > Strongyloidea > Cyathostomes CYATHOSTOMES AKA Small strongyles Live as adults in large intestines of horses, pigs, and wildlife Disease: Larval cyathostominosis: Watery diarrhea with hypoalbuminemia in late fall to early spring associated with emergence of large numbers of encysted larvae in mucosa Considered a rare manifestation of infection Diagnosis: Strongyle-type eggs on fecal flotation Larval culture for L3 identification Treatment: Adults resistant to benzimidazoles and pyrantel, most still susceptible to ivermectin (but resistance developing) Nematoda > Secernetea > Rhabditida > Strongyloides STRONGYLOIDES Tiny parthenogenic female nematodes Lives in mucosal crypts of small intestine Strongyloides westeri in horses Transmammary transmission occurs Disease: Diarrhea in foals Diagnosis: Eggs containing rhabditiform larvae in feces Treatment: Macrocyclic lactones, benzimidazoles Nematoda > Secernetea > Ascaridia (roundworms) > Parascaris PARASC ARIS Very large nematode Acquired through ingestion of infective eggs containing L3 Larvae migrate through liver and lungs Worm burden typically highest around 5 months old, then begins to wane Disease: Can cause bowel perforation and peritonitis Diagnosis: Eggs on fecal flotation, ultrasonography Treatment: Pyrantel pamoate, piperazine, benzimidazoles, macrocyclic lactones Resistance to macrocyclic lactones reported  FECAL EGG COUNT REDUCTION TEST (FECRT) Recommended yearly by American Association of Equine Practitioners (AAEP) to ensure dewormers are working Also useful for other species where resistance is a consideration Deworm and repeat fecal test 10-14 days after initial treatment Should see 95% reduction in egg count if dewormed is working  ACTIVE LEARNING ACTIVITY You are a veterinarian working with the owner of several horses, with a history of strongyle infections in his herd.You receive the following results from fecal flotations: Patient ID Parasite Parasite count Starlight Strongyles 200 eggs/gram Eimeria 100 oocysts/gram Moonbeam Strongyles 600 eggs/gram Sunnyboy Eimeria 50 oocysts/gram What is your next mode of action?  ACTIVE LEARNING ACTIVITY You elect to treat Moonbeam, based on the high shedding of strongyle type eggs.You also request a larval culture to evaluate for large strongyles in this population of parasites. Are there any additional steps you should might want to consider?  ACTIVE LEARNING ACTIVITY Nematode larval culture identifies the following: Patient ID Parasite ID Starlight Cyathostomins Moonbeam Cyathostomins Are there any additional steps you might want to take?  ACTIVE LEARNING ACTIVITY Following treatment with fenbendazole, you repeat a fecal flotation test for a fecal egg count reduction 2 weeks later, and it reveals the following: Previous Current Patient ID Parasite Parasite count Patient ID Parasite Parasite count Starlight Strongyles 200 eggs/gram Moonbeam Strongyles 400 eggs/gram Eimeria 100 oocysts/gram Moonbeam Strongyles 600 eggs/gram Sunnyboy Eimeria 50 oocysts/gram Are there any additional steps you might want to take?  ACTIVE LEARNING ACTIVITY Following treatment with moxidectin, you repeat a fecal flotation test for a fecal egg count reduction 2 weeks later, and it reveals the following: Previous Current Patient ID Parasite Parasite count Patient ID Parasite Parasite count Moonbeam Strongyles 400 eggs/gram Moonbeam None detected - Are there any additional steps you might want to take? MY HORSE IS COUGHING Nematoda > Secernentea > Strongylida (bursates) > Trichostrongylida (threadworms) > Dictyocaulus DICTYOC AULUS Live as adults in the respiratory tract of horses First-stage larvae passed in eggs often hatch before passing into feces Dictyocaulus arnfieldi: Equids Disease: Chronic bronchitis Typically nonpathogenic in donkeys Diagnosis: L1 in feces via Baermann method Treatment: Macrocyclic lactones, benzimidazoles MY HORSE IS BEHAVING STRANGELY  ACTIVE LEARNING ACTIVITY List some causes of neurologic signs in horses, and what tests you could run to rule in or out your differentials. Protists > SAR > Apicomplexa > Coccidians > Sarcocystis SARCOCYSTIS NEURONA Equine Protozoal Myeloencephalitis (EPM) Horses infected via ingestion of sporocysts from opossum feces Disease: Asymmetric ataxia, weakness of limbs, muscle atrophy most commonly Diagnosis: PCR test of cerebrospinal fluid, ELISA, antibody titers, postmortem examination Treatment: Ponazuril, diclazuril, sulfonamides + pyrimethamine Nematoda > Secernetea > Strongylida (bursates) > Metastrongyloidea (lungworms) > Parelaphostrongylus PARELAPHOSTRONGYLUS TENUIS AKA Meningeal worm Live as adults in the meninges of white-tailed deer definitive hosts Snails and slugs ingest larvae, and larvae develop to L3 Development in abnormal hosts (sheep, goats, camelids, cattle, horses) leads to fatal neurologic disease Diagnosis: No larvae passed in feces of abnormal hosts Diagnosis presumptive based on clinical signs Treatment in aberrant hosts often unrewarding Nematoda > Secernetea > Rhabditida > Halicephalobus HALICEPHALOBUS GINGIVALIS Tiny nematode with rhabditiform esophagus No males reported in lesions, parthenogenic species Infection via contamination of wounds, then hematogenous spread Disease: Present in nasal and maxillary sinuses, gingiva, kidneys, heart, brain, spinal cord Can cause fatal meningoencephalomyelitis in horses and humans Diagnosis: No eggs passed, typically diagnosed on necropsy Treatment: No approved treatment, poor prognosis with CNS involvement PRACTICE QUESTIONS