Atlas of livestock parasites
digitized collection of microscopical preparations

Atlas of Parasites Contents Information sources Glossary Administration

Strongyloides stercoralis (dog, cat)



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"intestinal threadworm"                  

Distribution: Worldwide, but more predominant in southern Europe.  

Host: Adult females live in the canine small intestine. Final hosts are dogs, humans and cats with ingestion of embryonated eggs from soil or fur, larvae in milk or paratenic hosts.  In utero from dam.  Pre-patent period is variable from 9 days and patent period can be several months (3 - 15 months).    

Life Cycle: Strongyloides parthenogenetic females in the small intestine release larvae that may develop into infective parasitic larvae or, alternatively, may undergo a single free-living cycle of         maturation and reproduction before infective parasitic larvae are formed. Infection of the host fromthe environment is primarily through skin penetration. Transmammary transmission may also occur if the dog is newly infected during lactation.     

Diagnosis: Finding large numbers of the characteristic eggs in very young animals, usually in the first few weeks of life, are suggestive of strongyloidosis. First-stage larvae may be identifed in fresh feces using a Baermann test.  Strongyloides larvae do not have the modifcations of the tail seen in most lungworm larvae. They  closely resemble hatched hookworm larvae or free-living nematodes that may be present in fecal samples that have been allowed to sit for a period of time prior to collection. If identifcation of the frst-stage larvae is uncertain, larvae in the feces can be cultured for a few days, and the third-stage larvae can be identifed.      

Size: 150–390 µm in fresh feces.

Strongyloides larvae can grow quickly in the environment  and their size increases before the molt to the second larval stage. This results in a large size range for the larvae. In addition, the size range may be increased by the mistaken identifcation and measurement of larger second-stage larvae.            

Clinical features:  Bloody diarrhoea, dehydration and sometimes death. Infections may be subclinical, but heavy infection can produce respiratory signs from migrating larvae as well as enteritis associated with adults. Strongyloides stercoralis  also infects humans and may produce severe and even fatal infections in immunocompromised humans. The degree to which canine strains infect humans is unclear, but because of the seriousness of some human cases, infection in dogs should be considered a zoonosis !   

Zoonosis: can cause several forms of disease:


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