Infection and immunity in dogs infected with a human strain of Strongyloides stercoralis.

The course of infection and immunological responses in dogs infected with a strain of Strongyloides stercoralis of human origin were investigated. The first dog infected developed a chronic infection lasting at least 15 months. Larvae disappeared from the faeces by three months after infection in another four dogs; these animals were resistant to challenge infection. A further dog developed a chronic infection of low intensity which could not be boosted by repeated heavy infections. These differences may be genetically determined. Immune responses in primary infections were measured in four dogs. A blood eosinophilia occurred in infected animals. Anti-Strongyloides antibodies of the IgM class appeared one week after infection, peaked at three weeks then slowly declined in titre while IgG antibodies appeared slightly later and then persisted in high titre. When compared with uninfected control dogs, no significant differences were seen in PHA stimulation of peripheral blood lymphocytes, nor did significant lymphocyte proliferation occur in the presence of Strongyloides antigen. Infected dogs showed marked immediate hypersensitivity to antigen injected intradermally, but Arthus and delayed hypersensitivity reactions were not seen. This model of human strongyloidiasis merits further investigation.