Superfamily Strongyloidea

Question 1

Superfamily Strongyloiodea

Answer 1

• Large and small strongyles (equine host)
• -Large strongyles:
• –Strongylus vulgaris
• –Strongylus edentatus
• –Strongylus equinus
• -Small strongyles (~40 species)
• –Cyathostomes
• Other parasites
• -Oesophagostomum spp.
• -Stephanurus dentatus

Question 2

Large and small strongyles

Answer 2

• Large buccal cavity
• Leaf crowns (corona radiata)
• Dorsal gutter
• +/- teeth
• Strong and powerful esophagus
• Worldwide distribution
• Direct life-cycle
• -Fecal-oral route
• -Migration differs between large and small strongyles

Question 3

Large strongyles

Answer 3

• Subfamily: Strongylinae (4 genera), 1.5-4.5 cm
• Migrate through various organs before returning to the large intestine
• Feed on blood; travel through blood vessels
• PPP is almost a year

Question 4

Small strongyles

Answer 4

• Subfamily: Cyathostominae (40 species), 0.6-2 cm
• Migrate through mucosa in the intestine
• PPP is 2-3 months

Question 5

Large and small strongyle larval ecology

Answer 5

• Development on pasture is very important in their epidemiology
• -Development to L3 (infective larvae) occurs in 1-2 weeks
• -Infective larvae can overwinter
• -Infective larvae are very resistant to desiccation
• Horses tend to have many more small strongyles than large strongyles

Question 6

Strongylus vulgaris

Answer 6

• 1.5-2.5 cm
• Two ear-shaped teeth in buccal cavity
• Migrate to the cranial mesenteric artery
• PPP is 5.5-7 months
• Most pathogenic
• Can cut off blood supply as it travels through the vasculature
• Adults
• -Active blood feeders
• -Ingest mucosal plug
• -Cause ulceration, fluid-loss, and anemia
• Larvae
• -Larval migration inflicts greater damage
• –Damage to cranial mesenteric artery
• –Interferes with blood flow to the intestines
• –Thromboembolism, colic, gangrenous enteritis, torsion, intussusception, and rupture
• —Can cause ischemia –> infarct –> gangrene

Question 7

Strongylus edentatus

Answer 7

• 2.5-4.5 cm
• Devoid of teeth in buccal cavity
• Migrate through the liver - hepatorenal ligament
• PPP is ~ 1 year
• More prevalent

Question 8

Strongylus equinus

Answer 8

• 2.5-4.5 cm
• Has one large and two small buccal cavities
• Migrates through the pancreas and liver
• PPP is 8-9 months
• Prevalence and pathogenicity is rare

Question 9

Cyathostomes

Answer 9

• Pathogenic effects are less dramatic than large strongyles
• -Adults are relatively harmless
• -No systemic migration of larvae (stay in intestinal mucosa)
• Most important nematode of horses
• L3 can undergo arrested development (for up to two years); encyst in fibrous nodules in cecal mucosa
• -Larval cyathostomiasis

Question 10

Larval cyathostomiasis

Answer 10

• Mass emergence of encysted larvae (pathology begins)
• Profuse watery diarrhea, severe inflammation of cecal mucosa, progressive weight loss, anemia, ventral edema, and dehydration (can become fatal)

Question 11

Large and small strongyle eggs

Answer 11

• Both large and small produce similar eggs - “strongyle-type eggs”
• -Oval, thin-shelled, multicellular
• 75-100% of the eggs passed in a naturally infected horse are from small strongyles
• Readily detected by fecal floatation
• Larvae may look like pinworms microscopically (but pinworms are MACROscopic)

Question 12

Large and small strongyle treatment

Answer 12

• Large strongyles: not common in US
• Small strongyles:
• -Adult worms - wide range of anthelmintics are effective
• -Encysted larvae:
• –Pyrimidines and ivermectin - not efficacious
• –Moxidectin - variable
• –Benzimidazoles - effective at elevated doses
• —Maybe also with ivermectin added in

Question 13

Nodular and bowel worms

Answer 13

• Oesophagostomum spp. present in sheep, goats, cattle, and swine
• Direct life-cycle: similar to Trichostrongyles
• Pathogenicity:
• -Worse in younger animals
• -May be markedly pathogenic in sheep, cattle, and primates
• -Less so in swine
• Adults in the large intestine:
• -Catarrhal enteritis, thickened bowel wall, cecal and colonic edema
• Larval nodules are very large in sheep and cattle; worse reaction with increasing exposure, sensitization; nodules become suppurative, caseated
• -Interference with motility, digestion, absorption; rupture through serosa and cause peritonitis

Question 14

Stephanurus dentatus

Answer 14

• Kidney worm of swine
• Geographically restricted to areas that do not have severe winters
• Southeastern and south central USA - swine raised outdoors
• Confinement rearing - reduced incidence of kidney worm
• Will see eggs in the urine (looks like a Strongylid egg)
• Not zoonotic, but can still ingest them
• Routes of transmission
• -Ingestion of infective L3
• -Ingestion of transport host (earthworm)
• -Skin penetration by L3 (migrates to the lungs, then to systemic circulation)
• Migration through the host
• -Extensive migration in the liver (3-9 months)
• -Penetrate the liver capsule - retroperitoneal migration to reach perirenal tissues
• -Access to ureters - eggs in urine
• Pathogenesis
• -Adversely affects growth
• -Aberrant migration - condemnation of organs and tissues
• Treatment
• -Doramectin and fenbendazole