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.