Comparative evaluation of cell-mediated immune response in calves immunized with live-attenuated and killed Theileria annulata vaccines.

Tropical theileriosis is a tick-borne disease caused by the protozoan Theileria annulata and transmitted by numerous species of Ixodid ticks of the genus Hyalomma. The main clinical signs are fever, lymphadenopathy, and anemia responsible for heavy economic losses, including mortality, morbidity, vaccination failure, and treatment cost. Development of poor cell-mediated immunity (CMI) has been observed in the case of many bovine pathogens (bacteria, viruses, and parasites). Quantification of CMI is a prerequisite for evaluating vaccine efficacy against theileriosis caused by T. annulata. The current study evaluated the CMI in calves administered with two types of T. annulata vaccine (live attenuated and killed). We prepared a live attenuated T. annulata vaccine by attenuation in a rabbit model and also prepared killed vaccine from non-attenuated T. annulata. For the evaluation of immune response in experimental groups including control, 20 calves were divided into four different groups (A, B, C, and D). They were either inoculated subcutaneously with live rabbit-propagated-Theileria-infected RBCs (5 × 106) (group A) or with killed T. annulata vaccine (2 × 109 schizonts) with Freund's adjuvant (group B), along with an infected group (group C) and a healthy control group (group D). The protection of vaccinated calves was estimated with challenge infection. Our results showed that with a single shot of live-attenuated and killed vaccine with a booster dose elicited cell-mediated immune responses in immunized calves. We observed a significant elevation in CD4 + and CD8 + T cells in immunized calves. A significant difference in the CD8 + T cell response between the post-challenge stage of killed and live vaccine (p < 0.0001) was observed, whereas no other difference was found at both pre- and post-immunization stages. A similar finding was recorded for the CD4 + T cells at a post-challenge stage, where a significant difference was seen between killed and live vaccine (p < 0.0001). Another significant difference was observed between the CD8 + T cells and CD4 + T cells at the post-challenge stage in the live vaccine group, where there was a significantly higher induction of CD4 + T cell response (p < 0.0001).

Theileria annulata: Its Propagation in Rabbits for the Attenuation of Piroplasms in Cross-Bred Calves.

Tropical theileriosis caused by the protozoan; Theileria annulata is a tick-borne disease (TBD) transmitted by ticks of genus Hyalomma; is clinically characterized by fever, anemia, and lymphadenopathy; and is responsible for heavy economic losses in terms of high morbidity and mortality rates with reduced production. Infected red blood cells of T. annulata were inoculated into rabbits intraperitoneally, and propagation of T. annulata has been investigated. The current study has shown an association between induced tropical theileriosis and variation of body temperature in rabbits. A significant rise in temperature (39.92 ± 0.33 °C) was seen on day 8 onwards, with the maximum temperature (40.27 ± 0.44 °C) on day 14 post-inoculation. In the current study, in vivo trials in susceptible cross-bred calves to investigate the attenuation and comparison with the infected group were also conducted. All the infected calves (n = 5) showed a significant rise in temperature (40.26 ± 0.05 °C) on day 10 onwards, with the maximum temperature (40.88 ± 0.05 °C) on day 16. The temperature of inoculated calves increased gradually post-inoculation, but the difference was not significant. A maximum parasitemia of 20% was observed in infected calves, but no piroplasm parasitemia was observed in inoculated calves. The prescapular lymph nodes of infected calves were enlarged, while the lymph nodes of inoculated calves remained normal throughout the trial. Analysis of clinical and parasitological responses of infected and inoculated calves showed a significant difference (p ≤ 0.05) in terms of temperature, parasitemia, and lymph node scoring between two groups. The current study was primarily aimed to attenuate T. annulata in rabbit and to check its virulence in susceptible calves. It is concluded that propagation of Theileria annulata in rabbits made it attenuated. Rabbit can be used as an in vivo model to weaken the virulence of T. annulata.