Exam 3: GI Parasites of Horses

generally define gastric spirurid nematdes

• Habronema muscae

• Habronema microstoma

• Draschia megastoma

generally describe gastric spirurid nematodes

• all require a fly host such as house or stable flies

• adult worms are small

• L3 may penetrate wounds and tissues, producing lesions

• because they utilize flies as intermediate hosts, infections tend to be seasonal “summer sores”

• infections are rare in well managed facilities

what are the major forms of gastric spirurid infection

• gastric

• conjunctival

• cutaneous “habronemiasis”

describe infection caused by Habronema spp

• inhabits the mucus layer of the gastric mucosa

• may cause catarrhal gastritis

• adult infections are not considered important

describe infection caused by Draschia megastoma

• fundic region

• provokes formation of large, tumor like masses near the margo plicatus

• masses contain worms

how is gastric habronemiasis diagnosed

• small larvated eggs may be difficult to find by standard fecal flotation methods

• eggs may be identified in gastric lavage fluids

• characteristic lesions in the stomach with Draschia

how is cutaneous habronemiasis diagnosed

• regional, farm, animal history

• charcacteristic lesions in aberrant sites once tumor, fungal/bacterial granuloma, others

• cytology for eosinophilia

• biopsy

• PCR

generally describe Trichostrongylus axei

• adults inhabit glandular portion of the equine stomach

• adult worms are small, measuring just 8mm

• eggs are strongyle type and are not usually differentiated from equine strongyles (smaller, one end slightly pointed) though larvae may be cultured for identification

• lacks host specificity among livestock, infection is only common where horses are pastured with ruminants

what are the important small intestinal nematodes

• Strongyloides westeri

• Parascaris equoruum

• Parascaris univalens

generally describe infection and transmission of S. westeri

• nursing foals and weanlings

• parasitic and free living cycles

• transmammary is most important (may be infected at 5 days of age)

• skin penetration

• ingestion

describe the pathogenesis of S. wsteri infection

• larvae migrate via venous system through lungs to develop in small intestines, PPP= 6-10 days

• immunity to adults develops within 6 months

• eggs are nearly only seen in nursing and weanling foals

what are the clinical diseases associated with S. westeri

• Catarrhal enteritis- “foal heat” diarrhea at 9-13 days post partum, corresponding to post-partum estrus

• respiratory distress

• dermatitis- frenzy syndrome- massive percutaneous penetration

• no clinical signs in adult horses

how is S. westeri diagnosed

• clinical signs

• finding eggs in feces

generally describe equine roundworm

• Parascaris equorum and P. univalens- common infection in foals

• large, robust, small intestinal ascarids

• major pathogen of foals and weanlings, horses >12-24m are largely resistent

• adult worm burdens peak at 4-5 months of age

what are important life cycle features of equine roundworms

• eggs become infective L3 within 14 days

• eggs may live >10 years on pasture and are highly resistant

• female worms may produce >200,000eggs/day

• no vertical transmission from mare to foal

• adult worms feed on intestinal contents and compete with host

• PPP= 80-110 days

• foals self cure at 6m

what are the clinical signs of equine tapeworms

• foals may develop coughing, nasal discharge and airway mucus

• other common signs include unthiftiness, rough hair coat, pot belly and stunted growth

• heavy infections may cause colic, and even intestinal blockage and ruptre

• infection is accompanied by a marked eosinophilia

what is the pathology of equine roundworm

• liver
  -small focal hemorrhagic tracts with eosinophils
  -as lesions resolve, fibrotic foci remain

• lungs
  -petechial hemorrhage, eosinophil infiltration
  -subpleural lymphocytic nodules up to 1cm in size

• Small intestine
  -potential intestinal impaction/rupture in foals following treatment with a paralytic

how is equine roundworm diagnosed

• fecal floatation

• finding worms in manure

• surgery or necropsy

what are the large intestinal nematodes in horses

• small strongyles

• S. vulgaris

• S. equinus

• S. edentatus

• Oxyuris equi

generally define small strongyles (Cyathostomes, Cyathostomins)

• currently most important parasite pathogen of equids when present in large numbers

• treated as a group and little is known about indivdual species

• small to medium sized, males are bursate

• all live in cecum and ventral colon

describe the life cycle of Cyathostome

• L3 develop directly or enter hypobiosis, surviving up to 2.5 years before resuming development

• PPP= 5-12 weeks depending on species

describe the epidemiology of Cyathostome

• seasonal transmission

• peak in gulf coast is late september to april

• hypobiosis is seasonal and greatest during late winter and spring

• hypobiotic L3 makes up majority of population in host

describe the pathology caused by Cyathostome

mildly thickened and edematous large intestinal mucosa with eosinophilic infiltration

describe the clinical disease caused by Cyathostomiasis

• poor growth and development

• colic that is non fatal with sudden onset in young horses <4 years

• profuse diarrhea with no other obvious cause

• seasonal

• infection with large numbers of L3 may cause similar signs

• low grade, increased frewuency of colic has been associated with increased burdens

how is cyathostomiasis diagnosed

• clinical signs

• strongyle-type eggs in quantitative fecal

• L3 cultures to differentiate from large strongyles

• larvae are swept into species

• <200EPG= low contaminator

• 200-500= moderate

• >500= high

what are the important large strongyles

• infect equine large intestine

• S. vulgaris (most pathogenic equine helminth, but not the most common!)

• S. edentatus

• S. equinus

how are large strongyles generally defined

• adults are medium to large, with a large buccal capsule bearing a corona radiata ± teeth

• blood feeders

• long PPP >6m
  -S. vulgaris= 6-99
  -S. edentatus= 9-12
  -S.equinus= 8-9

describe the life cycle of large strongyles

• direct, just like small

• consumed from the grass

describe the pathology caused by Strongylus vulgaris

• L4 cannot escape through the internal lamina so they migrate ithin the walls of major arteries, causing aortic aneurysms, thrombosis of cranial mesenteric and other arteries

• infarction of the gut vasculature → necrosis and colonic death

• horses rapidly develop compensatory collateral circulation

describe the pathology and disease of Strongylus edentatus

• larvae are not as pathogenic despite being 2x bigger than vulgaris

• L3 enter cecal/colic all → migrate via the portal veins to the liver → nodule formation → molt to L4 → hepatic migration → peritoneal migration → cecum → adhesions, colic

describe the pathology of Strongylus equinus

L3 enter the cecal/colic wall → nodular formation → molt to L4 → transverse peritoneum to right half of liver (which contacts cecum) → hepatic migration → enter pancreas/abdominal cavity → molt to L5 → penetrate large intestinal wall → lumen

how are large strongyles diagnosed

• strongyle type eggs in fecal floatation exam- need to culture

• no pathognomotic clinical pathologic changes of S. vulgaris but may include
  -neutrophilia that progresses to eosinophilia
  -normocytic anemia
  -increased serum total protein
  -decreased serum albumin
  -increased serum beta globulin

generally define Oxyuris equi (equine pinworm)

• pinworm species found in the equine small colon

• medium to large worms with pointed tails

• no tissue migration, but migration of adult to cement eggs in the perianal region causes pruritus

• cementing fluid containing embryonated eggs, dries and flakes off, contaminating the environment

describe the life cycle of Oxyuris equi

• PPP= 5 months

• eggs develop to L3 stage in 4-5 days

• eggs are operculated, with one side flattened and the other convex, ofte larvated

how is Oxyuris equi diagnosed

• rat tail appearance of tailhead

• eggs will be seen on fecal floatation if present are rare

• collect from perianal region with clear tape, scrape with tongue depressor/lube

generally define Setaria equina

• Filarioid nematode that infects horses, mules, donkeys in US

• mosquitoes are vector, PPP= 8-10m

• adult worms are found INCIDENTALLY in abdominal cavity

what are the major equine tapeworms and their locations

• Anoplocephala perforliata
  -common, large and small intestines

• A. magna
  -small intestine ± stomach

• Paranoplocephala mamillana
  -small intestine

• one tapeworm generation per year

describe the life cycle of equine tapeworms

• tranmitted to horses by mites that are ingested accidentally

• develop in horse 1.5-2months

• develop in mite 2-4 months

define Anoplocephala perfoliata by location, size, eggs, scolex

• ileum, ileocecal junction, cecum, upper colon

• smaller, up t8 8cm

• larger

• lappets at base of scolex

define Anoplocephala magna by location, size, eggs, scolex

• jejunum ± stomach

• up to 80cm

• smaller

• without lappets

describe the pathology of equine tapeworms

• lesions are associated with the accumulation of parasites at the ileocecal junction

• pathology is uncommon but may include inflammation, ulceration, small intestinal rupture, ileal obstruction, intussusception

• unthriftiness, anemia, colic

how do you do antemortem diagnosis of equine tapeworms

• eggs only found in about 50% of infected horses on fecal

• serum ELISA used in UK

what are the species of equine stomach bots

• Gasterophilus intestinalis

• Gasterophilus nasalis

• Gasterophilus hemorrhoidalis

• 1st-3rd larval stages are obligate parasites

describe the life cycle of Gasterophilus spp

• eggs are deposited one at a time on the hairs of the face, chest and forelegs

• eggs hatch within 1 weeks and enter the oral tissues to embed for 1 month

• molt to 2nd instars, then pass to stomach

• molt to 3rd instars and attach to cardiac/pyloric portions or first part of SI

• develop for 8-10 months, pass in feces and pupate for 3-5 weeks

• seasonal cycle, gastric populations peak in fall, exit host in spring

• life cycle takes 1 year

describe G. intestinalis by egg location, larva location, spines, and incidence

• legs and chest

• non-glandular stomach

• 2 rows-blunt

• common

describe G. nasalis by egg location, larva location, spines, and incidence

• neck

• pyloris to duodenum

• 1 row

• less common

describe G. hemorrhoidalis by egg location, larva location, spines, and incidence

• nose-face

• rectum

• 2 rows sharp

• rare

describe Gasterophilus clinical disease of the mouth

• 1st instars occupy fissues on surface of tongue

• 2nd instars reside in gingival pockets at base of molar teeth and may cause parasitic periodontitis, lingual lesions (tunnels with air holes), chewing problems

• tunneling action excavates all tissues, including nerves and capillaries

what clinical disease does Gasterophilus cause in the stomach

pit like ulcers/erosions in the stomach, surrounded by hypertrophic mucosa cause mild gastritis, though large numbers may be present without clinical signs

generally describe Eimeria leuckarti in horses

• protozoa

• common in foals but clinical disease is rare

• small intestinal epithelium, PPP= 16-37 days

• oocysts are large, dark brown, and rarely seen, unless sheathers fecal floatation media is used