Infecção natural por Anaplasma marginale em bezerras de fazendas leiteiras da Região Metalúrgica, Minas Gerais

Abstract

The dynamic of Anaplusma margmale natural infections in calves was evaluated during a period of one year in two farms located in the "Metalurgica" Region of the Minas Gerais State. Brazil. Blood samples were collected weekly for determination of parasitemia. packed cell volume (PCV) and serology by the indirect Antibody Fluorescent Test (LFAT). The animals which were bom from March to July suffered the infection in October and November, independently of their age. while calves which were bom from September to December acquired the infection dturing the first days of life, presenting patent parasitemia from 30 days of life. During the patent period the PCV decreased after one week of infection, varying from 20 and 23%. Amongst the 56 calves studied 55 % were positive by IFAT. The maximum titles of antibodies were detected in calves older than 150 days. which corresponded to the period soon after the maximtun parasitemia. It was concluded that, in the studied region, transmission of A. marginale is influenced by climatic conditions and that calves bom during the dry season are more likely to acquire the infection when they are exposed to high transmission levels during the subsequent taining season.