BACKGROUND: Thrombocytopenia without clinical bleeding is a consistent finding in virulent canine babesiosis.

OBJECTIVES: The purpose of the study was to investigate the platelet index phenotype in Babesia rossi-infected dogs and the association with disease outcome. We hypothesized that an increased proportion of large, activated platelets would be present.

METHODS: Ninety-six infected and 15 control dogs were included. Babesia-infected dogs were further divided into survivors and nonsurvivors. Platelet count, mean platelet volume (MPV), platelet volume distribution width (PDW), plateletcrit (PCT), mean platelet mass (MPM), mean platelet component concentration (MPC), and platelet component distribution width (PCDW) were measured at presentation, and at 24 and 48 hours in admitted survivors.

RESULTS: Mortality rate was 13% (12/96). At presentation, compared to controls, PLT and PCT were significantly decreased in survivors and nonsurvivors (P < .001 for both). Mean platelet volume was significantly increased in survivors and nonsurvivors compared to the controls (P < .001 for both); however, MPM was only significantly increased in the survivors (P < .001). There were no differences between the survivors and nonsurvivors for any of the indices at presentation. Platelet count and PCT were significantly increased at 24 and 48 hours, and MPC significantly increased at 24 hours for admitted survivors compared to the values at presentation.

CONCLUSION: Large, activated platelets were significantly increased and may play a role in the lack of a bleeding phenotype, despite severe thrombocytopenia, in canine babesiosis.