ISSN 2398-2977      

Strongyloides westeri





  • Class: Nematoda 
  • Family: Strongyloididae
  • Superfamily: Rhabditoidea.
  • Genus:Strongyloides.
  • Species:westeri.


  • Greek: Strongylos - round and compact.

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Clinical Effects



Parasitic stages
  • Parasitic females in submucosa of anterior small intestine and L1 to L3 in lumen of intestine.
  • Parasitic L3 in liver, lungs and mammary tissues.

Free-living stages

  • L1 to infective L3 and L1 to parasitic male and female and then infective L3 in environment.


  • 1. Parasitic females.
  • 2. Autoinfective 3rd stage larvae.
  • 3. Parasitic 3rd stage larvae.
  • 4. 1st stage larvae.
  • 5. Infective 3rd stage larvae.
  • 6. Free living males and females   Free-living nematodes  .


Transmission from mare to foal
  • Transfer of infection from the mare to her foal occurs via transmammary transmission.

Horizontal transmission

  • Infective L3 in the environment penetrate the skin or are ingested to migrate and return to the intestine.


  • Autoinfective L3 penetrate the colon directly and then migrate to return to the intestine.

Pathological effects

  • The host immune response modifies the course of infection.
  • Infection of a naive animal results in an infection with a patent period of about 3 weeks to 3 months.
  • Internal autoinfection occurs early in the course of infection.
  • Gut level resistance (that does not involve IgA) soon occurs and an increasing proportion of larvae are now excreted as L1 in the feces.
  • Low level chronic infections can persist in intestine and tissues.
  • Immunosuppression during pregnancy can permit renewed fecal shedding of larvae and possibly transmammary transmission.
  • Marked immunosuppression can permit reactivation and massive autoinfection.
  • Most infections asymptomatic.
  • Heavy infections can cause yellowish milky diarrhea between 2 weeks to 4 months of age.
  • Parasitic females buried in the submucosa. Eruption of their L1 to the lumen causes a catarrhal enteritis in the anterior small intestine with inflammation, edema and petechial ulceration and hemorrhage.
  • Malabsorption, moderate to severe diarrhea which may be hemorrhagic, weight loss and dehydration result.
  • Mucosal ulcerations in the colon are probably due to penetration of autoinfective L3.
  • Petecchial and more severe hemorrhages in subpleural and parenchymal lung tissues, plus interstitial pneumonia in response to large numbers of migrating larvae, may induce respiratory distress.


Control via animal

  • Treat affected foals.
  • If recurring problems on a stud, carry out routine treatment of young foals at 1-2 weeks old.
  • Ivermectin   Ivermectin   (0.2 mg/kg) reduces levels of infection when mare is treated within 12 h of foaling.

Control via chemotherapies


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Molento M B, Antunes J, Bentes R N & Coles G C (2008) Anthelmintic resistant nematodes in Brazilian horses. Vet Rec 162 (12), 384-385 PubMed.
  • Kaplan R M & Little S E (2000) Controlling equine cyathostomes. Comp Cont Educ Pract Vet 22 (4), 391-395.
  • Proudman C J (1999) The role in parasites in equine colic. Equine Vet Educ 11 (4), 219-224.
  • Lind O E, Hoglund J, Liungstrom B L, Nilsonn O & Uggla A (1999) A field study on the distribution of strongyle infections of horses in Sweden and factors affecting fecal egg counts. Equine Vet J 31 (1), 68-72 PubMed.
  • Rolfe P F, Dawson, K L & Holm-Martin M (1998) Efficacy of moxidectin and other anthelmintics against small strongyles in horses. Aust Vet J 76 (5), 332-334 PubMed.

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