ANTIBODY-RESPONSE TO HEPATOZOON CANIS IN EXPERIMENTALLY INFECTED-DOGS

Canine hepatozoonosis is a disease caused by the tick-borne protozoan Hepatozoon canis. Five puppies were inoculated by ingestion of Rhipice phalus sanguineus ticks experimentally infected with H. canis, and all became infected with H. canis: gametocytes were detected in blood sme ars from four dogs and schizonts were observed in the spleen and bone marrow of the fifth. Antibodies reactive with H. canis gametocytes wer e detected by the indirect fluorescent antibody test (IFA), with IgM d etected initially in all dogs 16 to 39 days post infection (PI) and Ig G 22 to 43 days PI. The presence of gametocytes was first observed wit hin peripheral blood neutrophils in Giemsa-stained blood smears betwee n days 28 and 43 PI. Gametocyte-reactive antibodies were detected befo re the appearance of blood gametocytes in three of the four parasitemi c dogs and also in a dog with no observed parasitemia. The detection o f serum antibodies prior to the detection of blood gametocytes, or wit hout apparent parasitemia, suggests that antibodies reactive with game tocytes may be formed against earlier forms of the parasite developing in the parenchymal tissues. Sera of dogs experimentally infected with Babesia canis, Babesia gibsoni and Ehrlichia canis exhibited no react ivity when tested with H. canis antigen. Additionally, sera positive f or H. canis were not reactive with antigens of Toxaplasma gondii, Neos pora caninum, Leishmania donovani and E. canis. In conclusion, inocula tion of dogs with ticks infected with H. canis results in production o f antibodies reactive with peripheral blood gametocytes. Detection of IgG titres would be beneficial for the diagnosis of progressive infect ions with undetectable parasitemia, for seroprevalence studies, and as an adjunct to IgM titres in early infections. (C) 1998 Elsevier Scien ce B.V.