First description of the pathogenicity of Babesia vogeli in experimentally infected dogs

Babesiosis is a tick-borne disease that occurs worldwide with the most recognized Babesia species that infect dogs being Babesia canis, B. vogeli, B. rossi and B. gibsoni. While B. vogeli is reported in dogs worldwide, clinical and laboratory data on infections is based on reports of naturally infected dogs. To provide reliable data on the clinical and laboratory abnormalities associated with acute and more chronic infections in healthy dogs free of other tick-borne diseases, we experimentally infected dogs with a Chinese strain of B. vogeli. All of the six infected Beagles, three of which were splenectomized, became infected with B. vogeli detected in blood smears taken the day following infection and the organism detected by FRET-qPCRs in most blood samples (77/86; 90%) collected about every 4 days until the end of the experiment on day 95. All the infected dogs showed fever, partial anorexia and malaise that was more severe in the splenectomized dogs that did not gain weight for three weeks in the period after initial infection. Regenerative anemia, thrombocytopenia and decreased white blood cell counts were seen in all dogs but were more severe in the splenectomized dogs, of which two had life threatening infections and had to be removed from the study for treatment. Following re-infection on day 66, none of the dogs showed clinical signs and copy numbers did not change significantly although all the dogs were negative by FRET-qPCR on at least some of the subsequent sampling days. Laboratory values in the non-splenectomized dogs were relatively unchanged while in the splenectomized dog there was a temporary small increase in the platelet and white blood cell counts and a temporary slight worsening of the anemia. In summary, our study shows dogs experimentally infected with a B. vogeli strain from China develop only mild clinical signs that are followed by asymptomatic infections that can last for least 95 days. In splenectomized dogs, however, severe life threatening signs may develop.