Review of Common Internal Parasites of Equines

1. Review of Common Internal Parasites of Equines

2. Routine fecal examination of horses will reveal parasitism by four types of parasites. Strongyloides westeri, Parascaris equorwn, Strongyles (large and small, sp. are not distinguishable by eggs), and Anoplocephala sp. (eggs of the two important sp. in the U.S. are indistinguishable). However, other sp. of parasites occur and will be reviewed. If a more thorough explanation of the “Salient Points” or “Features of the Life Cycle” are necessary please refer to your corresponding lecture notes from the second year or an appropriate text.

3. Strongyloides westeri eggs (40-52 u x 32-40 u) Thin walled, larvated egg, typical of Strongyloides

4. Strongyloides sp. Life Cycle: Parthenogenic parasitic females are found in the small intestine of foals, animals become immune and the adults are not generally found in the intestine after six months of age, infection occurs, via milk, skin penetration and ingestion, these parasites have a short prepatent period (5-6 days) and may be found in very young horses.

5. Strongyloides westeri: Salient Points Pathogenicity is questionableRx, TBZ, IVM, other HZ, but not FBZ.

6. Parascaris eguorum eggs (90-100u) thick-shelled ,globular shape, eggs are not larvated in fresh feces, some eggs here contain the infective larvae.

7. Parascaris equorum emerging from a perforated portion of the small intestine, this may occur in heavy infections. Pathology due to migrating ascarid larvae is considered to occur .

8. Parascaris equorum Salient Points: An infection of foals, sucklings, weanlings and to a lesser extent in yearlings and 2 year olds. Prepatent period 10-13 weeks, Rx Piperazine, Organic Phosphates, PRT ,HZ, IVM.

9. Gastrophilus Almost all horses are infected with bots Gastrophilus intestinalis sometimes with G. nasalis and rarely in the U.S., G. hemorrhoidalis. Bots cannot be diagnosed by fecal examination. Finding eggs on the horse's hair is an indication of internal infection. Unless treated most horses are infected.

10. Gastrophilus spp. Life Cycle Features: The spp. vary slightly, in host site, larvae hatch (4-14 days), go through early tissue migration and attach to mucosa of G.I.tract, live there 8-10 months, pass out in feces, pupate, adults hatch from pupae (5-6 weeks) and deposit eggs on horse hair .

11. Gastrophilus sp. in stomach Heavy infection, G. intestina/s attach preferentially to the white cardiac portion of the stomach and G. nasalis attach preferentially to the pyloric region. G. hemorrhoidalis attach in the rectum. Large numbers have been reported to cause mechanical blockage and/or rupture of the stomach, but this is unlikely.

12. Gingival erosions-due to early Gastrophilw migrations, pharyngitis may also occur

13. Gastrophilus spp. Salient Points Fly season April to Dec. in Louisiana, peak season is in the fall Rx organic phosphates ,all stages, IVM, all stages.

14. Three sp. of spirurid nematode occur as stomach worms in horses (Habronema mwcae, H. microstoma and Draschia megastoma). These are difficult to diagnose as internal infections because eggs or larvae are rarely found by standard fecal flotation methods. One sp. of Trichostrongyle stomach worms also occurs in horses (T. axei) eggs are simi]ar to strongyles, but vary slightly in size (79-92 u x 31-41 u) and shape (slightly flattened and pointed at one end).

15. Cutaneous habronemiasis: “Summer Sore” on the prepuce of horse, develop from larvae being deposited or escaping from vector flies feeding around a wound or abrasion. May also cause pulmonary granulomas if larvae invade the lungs. In the stomach Habronema sp. produce mucus exudate, and D.megastoma produce tumor- like lesions along the margoplecates

16. Salient Points -Horse Stomach Worms– Indirect life cycle, Rx IVM. T. axei -BZ, IVM.

17. Oxyuris equi egg(42-90 u) Eggs are elongated and slightly flattened, with a operculum like plug at one end, these are rarely seen in feces.

18. Oxyuris equi adult females: More commonly found in foals, females rupture during their migrations to the rectum and anus, eggs are released and attach to walls, fixtures, etc. , development to infective larvae within the eggs is fast, (3-5 days), prepatent period -5 months

19. Loss of Hair: Due to pruritus caused by migrating female 0. equi, this irritation and resulting hair loss is the principle problem associated with the infection, and the common means of diagnosis

20. Oxyuris equi Salient Points Pinworm infections are mainly but not only a problem in stabled horses, 8 Rx: most all drugs.

21. Anoplocephala sp. Eggs -(50-60 u) Eggs possess pyriform apparatus, spp. identification is not possible on egg morphology .

22. magna in horse intestine: • Largest (up to 12 in) of two common spp. in the U.S. found in posterior portion of small intestines may produce catarrhal or hemorrhagic enteritis

23. Anoplocephala perfoliata adults: Smaller than A. magna (1-2 in.) occur in larger numbers more , pathogenic of the two spp. , produces ulcers, and may induce occlusion of ileo-cecal valve, or intussusception in this area.

24. Anoplocephala spp. Salient Points: Indirect life cycle ….orbatid mites are intermediate hosts; Rx, Pyrantel is effective against Anoplocephala spp.

25. . Strongyle egg -{70-85 u x 40-47 u) Spp. cannot be identified by egg morphology , egg here can be compared to Parascaris equorwn and Strongyloides westeri.

26. The large strongyles are pathogenic because of their larval migrations, adults attach to the mucosa of the large intestine and cecum and suck blood. Some Triodontophorus spp. produce mucosal ulcers

27. Strongylus vulgaris caused aneurism in mesenteric artery due to larval migrations

28. Strongylus vulgaris related intestinal infarction Due to emboli produced by S. vulgaris larval migrations in mesenteric, arteries. Other large strongyle larvae (S. edentatus & S. equinus) produce lesions during their migrations in liver, diaphram and other viscera. .

29. Comparison of large and small strongyles

30. Large strongyles Salient Points: Infections by ingestion occur early but eggs are not produced until 6 months (S. vulgaris), 9 months (S. equinu) and 11 months (S. edentatus) prepatent periods are shorter for small strongyles (6-12 weeks). Rx -BZ, Pyrantel, IVM (adults).

31. Cutaneous Onchocerciasis Chronic dry dermatitis due to microfilarial presence in skin, life cycle is filarid type, vector Culicoides sp. adults occur in ligamentum nuchae.

32. Onchocerca cervicalis Salient Points: Dx: microfilaria in skin snip IVM as a microfilaricide

33. Babesia cabaIli – Large sp. has been in the past described in southern U .S. (F1a.), Dennacentor nitans vector in U.S.

34. Babesia equi: (Small spp.) Only a few cases have been described in the U.S., more pathogenic than Babesia caballi - Babesia spp. Remain a threat from horses imported from South America, Africa, and Asia .

35. Trypanosomes -T. evansi causes surra, (Africa, Asia, Central & South america) Transmission is mechanical by biting flies. T. equiperdwn causes dourine, (Asia, Africa, Europe, Mexico) a venereal disease.

36. Many other sp. . of larval and adult helminth and protozoan parasites occur less commonly in horses. A complete list of these can be found on page 796- 797 in the 6th edition of Soulsby's Helrninths. ArthrQ12:Qds and Protozoa of Domesticated Animals (Monnig) or in Drudge & Lyons, Internal Parasitesof Horses.