Clinical and immunomolecular monitoring in cattle infected with virulent or attenuated Babesia bigemina microorganisms

• DOI: 10.22533/at.ed.973322310023

• Palavras-chave: -

• Keywords: Babesia bigemina; virulent strain; attenuated strain; virulence genes.

• Abstract:

  The objective of this work was to carry out comparative clinical, serological and molecular monitoring of animals inoculated with virulent or attenuated microorganisms of B. bigemina. Seven cattle were used, one of which was splenectomized to reactivate the virulent strain cryopreserved in liquid nitrogen. The remaining 6 cattle were randomly grouped into Groups I (GI), inoculated with 1x10⁸ erythrocytes infected with B. bigemina virulent strain, and GII inoculated with 1x10⁸ erythrocytes infected with B. bigemina, attenuated strain, derived from in vitro culture. Daily monitoring included taking rectal temperature (°C) value and collecting blood to determine: Packed Cell Volume (PCV) and Percent of Parasitized Erythrocytes (PPE). In addition, the Indirect Fluorescent Antibody Test (IFAT) and the nested PCR test (nPCR) were used. A PPE >9% was determined in the splenectomized calf, obtaining biological material for GI inoculation. The IG animals showed severe clinical signs, associated with acute babesiosis, with fever >41°C, hemoglobinuria, PPE >5% on day 5-6 Post-Inoculation (PI) and decrease in PCV from day 4 PI, with a minimum PCV of 11.3% at the end of the monitoring. Animals were treated with babesiaside to prevent death. The GII cattle did not present fever or signs of acute babesiosis, presenting only a slight decrease in PCV (HT value of 25%), and PPP <0.1%. No GII cattle required treatment. Seroconversion was identified on day 7 PI, with a maximum antibody titer of 1:1280 on day 14 PI in the GI. In the GII, a maximum antibody titer of 1:2560 was determined. The nPCR test confirmed the presence of B. bigemina in the animals, visualizing DNA fragments of 170 bp in agarose gels. It is concluded that the strain kept in cryopreservation maintains its virulence when reactivated in a splenectomized calf, observing severe clinical signs in the inoculated animals. The attenuated strain, maintained in in vitro culture and used as a live vaccine, has not reverted to virulence, is innocuous, and is still immunogenic.