Propagation of Babesia bigemina in Rabbit Model and Evaluation of Its Attenuation in Cross-Bred Calves

SIMPLE SUMMARY: Vector-borne diseases (VBDs) cause heavy economic losses in the livestock sector. Among these VBDs, babesiosis is the second most common disease, causing high morbidity, mortality, and reproductive and productive losses in cattle. The causative agents of this disease are globally distributed across tropical and subtropical countries. In the current study, B. bigemina was propagated in vivo in rabbit for attenuation and evaluated for its virulence periodically. This attenuated B. bigemina was then inoculated to naive calves for the evaluation of clinical parameters. Increased parasitaemia and temperature were observed in rabbits following the inoculation of B. bigemina-infected red blood cells. The naive calves did not show symptoms of parasitaemia or temperature elevation when inoculated with rabbit-propagated B. bigemina-infected RBCs. Furthermore, this study also demonstrated that infected cattle periodically had a decreased PCV profile, along with increased temperature and parasitaemia. Moreover, this study also revealed correlations between the temperature, parasitaemia, and packed cell volume of inoculated, infected, and control group calves. ABSTRACT: Bovine babesiosis (BB) is a vector-borne disease (VBD) that affects cattle in tropical and subtropical areas, caused by the haemoprotozoa Babesia bovis and Babesia bigemina. It is transmitted by tick bites belonging to the genus Rhipicephalus and is clinically characterized by high fever, depression, anorexia, decreased milk and meat production, haemoglobinemia, haemoglobinuria, jaundice, and pregnancy loss. In this study, the propagation of B. bigemina was evaluated by intraperitoneally inoculating 3 × 10(6) red blood cells infected with B. bigemina into rabbits. The study showed that variations in rabbit body temperatures are related to induced bovine babesiosis. A significant increase in temperature (39.20 ± 0.23 °C) was observed from day 4 onwards, with the maximum temperature (40.80 ± 1.01 °C) on day 9 post-inoculation. This study included susceptible cross-bred calves for in vivo attenuation, and they were compared with an infected group. The calves in the infected group showed a significant increase in temperature (38.79 ± 0.03 °C) from day 3 onwards and a maximum temperature (41.3 ± 0.17 °C) on day 11. Inoculated calves showed a gradual rise in temperature post-inoculation, but the difference was not significant. Inoculated calves did not show parasitaemia, whereas 32% of infected calves displayed parasitaemia. As compared to inoculated calves post-inoculation, packed cell volume (PCV) decreased (16.36 ± 1.30) for infected calves. However, there were statistically significant differences (p ≤ 0.05) in temperatures, parasitaemia, and PCV in both inoculated and infected calves. The current study aimed to attenuate B. bigemina in rabbit models and evaluate the pathogenic potential of this organism in naive calves. In conclusion, B. bigemina proliferation was attenuated in rabbits. The rabbit model can be used to study B. bigemina in vivo in order to reduce its pathogenicity.