Persistent and disseminated infections with Strongyloides Stercoralis in immunosuppressed dogs

https://doi.org/10.1016/S0020-7519(83)80012-5Get rights and content

Abstract

The effects of immunosuppression on the course of infection in dogs infected with a human strain of S. stercoralis were investigated. Four dogs were infected then 4 weeks later, three animals were begun on prednisolone orally in a dose of 150 mg daily for 6 days each week. Rhabditiform larvae continued to be excreted in the stools. After 5 weeks of immunosuppression, one dog was autopsied; plentiful parasites were found in the upper small bowel but worms were not seen in other tissues. Similar findings were made in a second dog killed after 9 weeks of immunosuppression. In the third dog, the dose of prednisolone was increased to 225 mg daily 15 weeks after infection then azathioprine 100 mg daily was added 6 weeks later. This animal was killed 24 weeks after infection and evidence for multiplication of S. stercoralis was obtained. Large numbers of adult worms, eggs and rhabditiform larvae were recovered from duodenal fluid. Infective larvae were seen in homogenised lung, rhabditiform larvae were noted in homogenised spleen and both rhabditiform larvae and adult worms were found in homogenised kidney. Worms in all stages of development were seen in the urine. Histological examination revealed large numbers of adult worms and enormous numbers of eggs and larvae in the duodenal mucosa. Worms were seen throughout the length of the small intestine as well as in the colonic mucosa. The lungs displayed focal haemorrhages and larvae were seen in the alveolar spaces, bronchioles and bronchi. Evidence of immunosuppression was provided by the gross atrophy of the thymus and the fall in anti-Strongyloides antibody titres. In contrast to these dogs, larvae disappeared from the non-immunosuppressed dog by 13 weeks after infection. This animal was then immunosuppressed for 8 weeks but parasites could not be found in either the stools or at autopsy. Two further dogs were immunosuppressed before infection but they died soon thereafter. It is concluded that immunosuppression permits the persistence of infection with S. stercoralis and if continued for long enough and in sufficient degree, that disseminated infection supervenes. This model may provide a means for assessing the efficacy of various therapeutic regimens in overwhelming strongyloidiasis and for investigations of the host-parasite relationship in this infection.

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