Aspectos parastológico, sorológico e epidemiológico das infecções por Babesia bovis, Babesia bigemina e Anaplasma marginale em bovinos de leite

Abstract

Cattle tick fever (CTF) is a significant disease in livestock, caused by the protozoa Babesia bovis and Babesia bigemina, as well as the bacterium Anaplasma marginale. These pathogens are prima rily transmitted by the tick Rhipicephalus microplus, posing a serious problem in tropical and sub tropical regions such as Brazil. CTF is responsible for high mortality rates and economic losses due to decreased meat and milk production, in addition to the costs associated with control and treatment. The new dynamics of dairy cattle farming systems, across different stages of animal development, have a considerable impact on exposure to R. microplus. Recent studies have focused on characteri zing the genetic diversity of A. marginale, which plays a crucial role in accurate diagnosis through genetic sequencing. Thus, this study aimed to assess the infection dynamics of CTF agents in heifers from birth to first calving in the municipality of Jataí-GO, under exposure to R. microplus, correla ting parasitological, serological, and clinical aspects of the infection. Additionally, we evaluated the persistence of infection by BPS agents in cows raised with or without contact with R. microplus and analyzed the genetic diversity of A. marginale. Three studies were conducted. The first study invol ved 15 Girolando heifers (15/16 Holstein × 1/16 Gir), monitored from birth until first calving (be ginning of lactation), totaling 28 months of observation. The second study assessed cows between the 1st and 6th lactation, which were housed in compost barns during lactation and kept on pasture during the dry period. The third study evaluated cows from the 1st to the 7th lactation that had no further contact with R. microplus after their first calving. The animals were assessed based on para sitological, clinical, and serological parameters, as well as the genetic diversity of Anaplasma mar ginale. As for the results, calves raised on pasture in contact with R. microplus in a tropical region reached a BPS agent positivity rate of ≥75% by four months of age. BPS cases primarily occurred post-weaning, between 3 and 8 months of age. A correlation was observed in A. marginale bactere mia between qPCR and blood smear analysis, but no correlation was found between bacteremia and iELISA. Calves exposed to ticks between 3 and 8 months of age tended not to develop clinical BPS in adulthood, even when continuously exposed to R. microplus. Serological or molecular results for B. bovis and B. bigemina in cows should be interpreted with caution, as the presence of these agents in less than 75% of the herd may not indicate enzootic instability. Furthermore, cows exposed to ticks during the dry period exhibited higher A. marginale infection levels in the 5th and 6th lacta tions. Conversely, cows that had no further contact with R. microplus after their first calving displa yed higher A. marginale infection levels in their first lactation. The A. marginale msp4 genotypes reported in this study correspond to those previously documented in Brazil.