Equine Parasites Lecture Notes

EQUINE PARASITES Sarra Lord, B.S., LVT © 2016-2022  EQUINE PARASITES Horses are infected by a wide variety of parasites (over 150!) Grazing animals = continuous exposure Parasite control is vital for good health (control vs. elimination) Strategic deworming schedule (...

EQUINE PARASITES Sarra Lord, B.S., LVT © 2016-2022  EQUINE PARASITES Horses are infected by a wide variety of parasites (over 150!) Grazing animals = continuous exposure Parasite control is vital for good health (control vs. elimination) Strategic deworming schedule (daily vs. quarterly vs. PRN) Pasture Management Routine fecal examinations Fecal egg count Fecal egg count reduction testing  PASTURE MANAGEMENT Avoid overcrowding Clear manure from pasture 2x week and compost; do not spread it on pasture nature's process of recycling decomposed organic materials into a rich soil known as compost; anything that was once living will decompose Mow and harrow pastures periodically Rotate pastures when possible Keep foals in separate pasture Don't feed hay/grain from ground  EFFECTS OF EQUINE PARASITISM The host reaction varies from no effect to death depends on the pathogenic potential of the parasite and the number of parasites The severity of the disease is related to the age of the horse the duration of the infection the tissue damage and blood loss mechanical obstruction Most damage is done by migrating larval stages and not the adult worms EQUINE PARASITE VIDEOS The Parasite Puzzle Part 1 The Parasite Puzzle – Part 2  COMMON EQUINE PARASITES Large strongyles Small strongyles Roundworms Tapeworms Pinworms Lungworms Bots Threadworms Flukes Protozoans PARASITE PUZZLE PART III The Parasite Puzzle – Part 3 NEMATODES  LARGE STRONGYLES 3 species Strongylus vulgaris Strongylus equinus Strongylus edentatus These are the most destructive parasites of the horse Many colics are related to damage from these parasites These parasites feed by ingesting mucosal tissues Adult parasites in cecum and colon S. vulgaris (aka bloodworms, redworms) They migrate to the large intestine via the cranial mesenteric artery and cause vascular damage during the larval migration. This leads to decreased blood supply to the gut resulting in colic S. equinus, S. endentatus Larval migration through liver and peritoneal cavity (space between membranes that separate abdominal organs from abdominal wall)  STRONGYLUS VULGARIS Eggs resemble hook worm eggs but are larger Adults are small parasites (2cm) Life cycle eggs passed in feces; mature and hatch in pastures Develop into L3 in as little as 1 week; can survive extended time in moist environment L3 larva in pastures are ingested by the horse  STRONGYLUS VULGARIS Ingested larva enter cecal mucosa and develop to L4 stage in 1-2 weeks L4 migrate through the circulatory system through the cranial mesenteric artery and enter the large intestine Migration results in Arteritis – inflammation of the arteries Thrombosis – stationary blood clot Embolism – thrombus that has moved from one place to another Long prepatent period-6 months (Do not find eggs in foals under 6-11 months of age)  S. EQUINUS AND S. EDENTATUS Much larger adults (4-5cm) Life cycle: Similar up to L4 stage Migrates to liver leaves the liver and enters peritoneal tissues migrates to cecum then into the intestinal lumen within about 9 -11 months. Clinical signs poor weight gain/weight loss decreased energy Poor/dull hair coat recurring colic Treatment Pyrantel Fenbendazole Ivermectin STRONGYLUS FEEDING  SMALL STRONGYLES Make up the majority of the equine worm load Found in the mucosal lining of the large intestine and cecum About 40 different species Attach and feed on blood Result in less severe clinical signs than do the large strongyles  Life cycle eggs pass in the feces hatches into L1 which is free-living in the environment Molts to L2 then L3 and attaches to grass Ingested then penetrates the mucosa of the cecum SMALL Prepatent period approximately 6-14 weeks STRONGYLES Treatment Good de-worming program with rotating anthelmentics Paddock management: pasture rotation PARASITE PUZZLE PART 6 The Parasite Puzzle Part 6: Small an d Large Strongyles ASCARIDS  ASCARID – PARASCARIS EQUORUM equine roundworm, equine ascarid Egg: typical ascarid egg, thick shelled, dark brown center Highly resistant in the environment Sticks to mare’s udder and infects foal Adult: 8-19” long, females larger able to lay > 200,000 eggs/day per female Prediliction site – small intestine Prepatent period – 12-16 weeks Zoonotic? - No  ASCARIDS Life Cycle: direct, 10-12 week cycle Infective egg containing L2 larva swallowed larva hatches and burrows into intestinal wall carried to liver and then lung coughed up trachea and swallowed matures in the small intestine to adult Main source of food is the liquid contents within the intestinal lumen. They eat by sucking up the liquid while moving through the intestines.  CLINICAL SIGNS Clinical Signs: Poor growth (stunted)/weight loss Coughing/nasal discharge dull hair coat +/- diarrhea fecal (worm) impaction--colic ruptured intestine death Appears in foal feces at about 12 weeks of age  ASCARIDS Control: Sanitation – wash feeders and waterers Don’t feed from the ground Good deworming program Rotate pastures Treatment: Panacur Ivermectin Piperazine PARASITE PUZZLE PART 5: ASCARIDS The Parasite Puzzle Part 5 - Ascarids INTESTINAL THREADWORM  STRONGYLOIDES WESTERI Common name: Intestinal threadworm (of the horse) Very short and thin (~1 cm long) Prediliction site – small intestine Seen principally in suckling and weanling foals Mare can transmit through colostrum Larvae can also penetrate the skin Can cause diarrhea in foals at ~ 2 weeks of age  STRONGYLOIDES WESTERI Life Cycle Alternates free-living and parasitic generations There are NO parasitic male worms Parasitic females are parthenogenetic Produce larvated eggs (L1) that are passed in feces Eggs hatch -may develop to infective (L3) larva, or may mature to free living form- male and female; reproduce Foal infected by skin penetration of larva in environment OR transmammary transmission Larva migrate to lungs, coughed up, swallowed and mature in SI  STRONGYLOIDES WESTERI Prepatent period 5-7 days Foals passing eggs at 10-14 days age Diagnosis- fecal flotation, centrifugation Treatment- ivermectin NOT usually a problem in adult horses Foals develop immunity to intestinal threadworm by 3-6 months PINWORM  PINWORMS – OXYURIS EQUI Common name – equine pinworm Predilection site – cecum, colon, rectum Prepatent period – 4 -5 months Not very pathogenic – but do cause significant pruritus (itching) around perineum Rubs rump on fences, stalls, feed bins, other horses, etc Animals get restless – eat less – leads to weight loss and dull coat Zoonotic? – no (species specific)  OXYURIS EQUI Life Cycle Egg larvates and matures to infective L3 form in 3-5 days Horse ingests larvated egg, hatches in small intestine L3 passes to cecum, colon and enters mucosal lining Adult lives in lumen of cecum, colon Prepatent period 5 months Female migrates from colon through the rectum, extends her body to the anus and lays eggs Eggs laid perianally in clumps contained in a greyish-yellow gelatinous material = eggs cemented to the skin of the perineum = irritation = anal and perineal pruritus Eggs dry and fall to the ground or are rubbed off Diagnosis – scotch-tape test to collect eggs around anus Treatment – pyrantel, fenbendazole, ivermectin, others Wash hindquarters to remove eggs – break cycle PARASITE PUZZLE PART 7: PINWORMS The Parasite Puzzle Part 7: Pinworms LUNGWORM  LUNGWORMS – DICTYOCAULUS ARNFIELDI Common name – Equine lungworm Infects donkey, horses and mules More common in donkeys Donkeys usually asymptomatic – chronic coughing in horses Adult parasites live in the bronchi and bronchioles 3-6 cm long Prepatent period – 45 -60 days Can cause obstructions  DICTYOCAULUS ARNFIELDI Life cycle Larvated eggs passed in feces Eggs hatch, mature to L3 Ingested by horse, migrate to lungs and mature Prepatent period 8 weeks in donkeys; in horses many infections not patent Diagnosis- may find eggs or larva in feces or tracheal wash Treatment- ivermectin Prevent- horses should not graze with donkeys HABRONEMA AND ONCOCERCA  HABRONEMA MUSCAE Common name – Habronemiasis Stomach worms or summer sores Predilection site – stomach (adults); larvae (stomach or skin) Intermediate host – muscidae fly Adults are not very pathogenic – larvae are more harmful Prepatent period – 60 days Zoonotic? - No  HABRONEMA SPP. Life cycle Larvated eggs pass in feces eggs hatch, larva ingested by maggots (fly larvae) larva molts to L3 in 7 days L3 migrates to head of fly, deposited on tissue when fly feeding on horse if larva swallowed---mature in stomach if larva enter wounds--forms granulomas or “summer sores” difficult to treat; may not heal until cooler weather  HABRONEMA SPP Diagnosis- may find eggs or larva in feces; skin scraping or biopsy may find larva in cutaneous lesion Treatment Ivermectin is the drug of choice Prevention- fly control; remove manure from pasture; fly ointment around wounds ONCHOCERCA CERVICALIS Common name – Equine filarial worm, neck threadworm Intermediate host – biting midges (Culicoides spp.) Adults – 6 – 30 cm Zoonotic? - no  ONCHOCERCA CERVICALIS Life Cycle Adults produce microfilaria (L1) that migrate through dermis Biting midges ingest L1; matures to L3 Transmit L3 by biting another horse L3 migrate to dermis (usually neck or ventral midline), mature to adults  ONCHOCERCA CERVICALIS Clinical signs patchy alopecia scaling around the head, neck, and shoulders lesions on ventral midline intense pruritus Equine recurrent uveitis? Diagnosis- skin biopsy, or response to treatment Treatment- macrocyclic lactones to kill microfilaria; no treatment for adults Prevention – consider fly spray TAPEWORM  ANOPLOCEPHALA SPP Common name: Equine tapeworm Anoplocephala perfoliata (most common) Anoplocephala magna Paranoplocephala mamillana (dwarf ) Often asymptomatic but can lead to colic – more common in young and old horses Intermediate host – grain mites, pasture mites, oribatid mites Zoonotic? - no  ANOPLOCEPHALA SPP.  Life cycle  Proglottid containing eggs passed in feces  Egg is ingested by an oribatid grain mite  Cysticercoid forms in 2-4 months in the mite  Mite ingested and larva released  develop into adult worm in 6-10 weeks  Adult attaches to the intestine (cecum) producing ulcers and irritation  Prepatent period – 28 – 42 days  ANOPLOCEPHALA SPP. Diagnosis fecal flotations; centrifugation; gross examination ELISA test (A. perfiolata) Treatment Praziquantel (Zimectrin Gold) Pyrantel at 2x normal dose PARASITE PUZZLE PART 9 EQUINE TAPEWORM The Parasite Puzzle Part 9: Inside t he Equine Tapeworm The Parasite Puzzle Part 11: Tapeworm Damage OTHER GI PARASITES  GASTEROPHILUS SPP. Gasterophilus intestinalis Gasterophilus nasalis Common name – bots Predilection site – gastric mucosa  GASTEROPHILUS SPP. Life cycle The bot fly (resembles a honey bee) deposits eggs on the hair of the animal. Forelimbs, shoulders, legs, lips, submaxillary region, etc hatch in ~1 week. Larvae migrate into the oral cavity where it is warm and moist Larvae burrow into surface of the tongue where they spend a month L2 develop and migrate into the stomach L3 attach to the stomach lining for about 8-10 months In the spring, they pass out in the feces and pupate into flies within 3-9 weeks PARASITE PUZZLE PART 4 THE BOT FLY Parasite Puzzle Part 4 – Bot Flies PROTOZOANS  SARCOCYSTIS NEURONA Definitive host - opossum Intermediate hosts - have been found in cat, dog, armadillo, skunk, raccoon, otter, and seals Horse is an abberant dead-end host; not passed in manure Sarcocystis neurona is a protozoan parasite that enters the brain and spinal cord of horses causing Equine Protozoal Myeloencephalitis Gait abnormalities Weakness Dysphagia Head tilt, neurologic deficits  SARCOCYSTIS NEURONA Life Cycle- sarcocysts in intestine of opossum; sexual reproduction to produce oocysts which pass in feces Sporulated oocyst picked up by intermediate host (cat, skunk, raccoon, otter); asexual reproduction, then forms cysts in muscle tissue (sarcocysts); ingested by definitive host Horse - ingests sporocyst in food or water contaminated by opossum feces  SARCOCYSTIS NEURONA Treatment There are no drugs currently known that will kill the parasite, so once the horse has the disease, it is very difficult to treat. 4-12 week course of antiprotozoals and antiparasitics Ponazuril paste (anti-coccidial activity) that can cross the blood brain barrier (5mg/kg sid x28) Cost: $800-1200.00 per horse Doesn’t improve the CNS damage that occurs before treatment begins  SARCOCYSTIS NEURONA Prevention: Keep feed covered to decrease contamination Keep trash in closed galvanized metal containers Get rid of bird feeders around the stable area Trap and relocate opossums from the barn and farm Avoid feeding horses on the ground Prognosis: guarded for return to full function  EIMERIA SPP. Equine coccidiosis is an infection of the intestinal tract by protozoa of the genera Eimeria. Horses are infected by 3 species Prepatent period 16-35 days Coccidia are a common incidental finding in normal foals which suggests that this parasite doesn’t cause many clinical signs. Diagnosis – dark brown oocysts found in fecal flotation THE PARASITE PUZZLE PART 8 PARASITE LOCATIONS The Parasite Puzzle Part 8: Location of Parasites in Horses