Definitive diagnosis of infections from Babesia species relies on identification of piroplasms in erythrocytes on stained blood smears (Wright’s stain). However, although numerous organisms may be found in blood smears from acutely infected animals, parasitaemias are usually low and organisms are rarely found in samples collected from chronically infected dogs or asymptomatic carriers.

Serology may be useful in identifying the presence of antibodies to B. canis, which cross-react with those to B. gibsoni, thereby allowing indirect detection of previous infection with either organism.

Note: serologic testing in the diagnosis of Babesiosis has limitations. A positive test result is dependant on antibody response by the host, which may take a long time to develop. In acute infections, dogs with evidence of Babesia species may be serologically negative, necessitating repeat testing using convalescent sera.