Utilização de isolados de Anaplasma marginale de baixa virulência em protocolos de imunização de bezerros: análise dos efeitos pós-vacinais e proteção contra o desafio natural

Abstract

In order to evaluate the post-vaccination effects and the protection afforded by the inoculation of live samples of low virulence A. marginale (UFMG1 and UFMG3) in cattle challenged in the field. 68 calves Holstein with 17 days old on average were randomly divided into four groups. The groups received two subcutaneous applications with intervals of 40 days, having a dose of 2x106 infected erythrocytes of the following protocols: group 1 (UFMG 1 + UFMG 1); group 2 (UFMG 3 + UFMG 3); group 3 (UFMG 1 + UFMG 3); group 4 (experimental control). Every two days, the animals were evaluated by rectal thermometry, hematocrit and blood film. Before inoculations and challenge and at the end of the challenge, blood samples were collected and used to perform IFA technique and nPCR. On average, the rectal temperature and the packed cell volume remained within the limits of reference and without considerable changes. 40 days after the second inoculation 90%, 84.62% and 90.9% of the animals in groups 1, 2 and 3 respectively were positive in nPCR. The rickettsemia was of low intensity but some animals of all groups required medication to control post-vaccination effects. During the challenge 86.7% and 73.7% of the animals was protected in groups 1 and 2 respectively, whereas 58.8% of the control animals became sick.