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Evaluation of anaplasmosis in naturally infected crossbred-holstein calves challenged with homologous and heterologous isolates of Anaplasma marginale

Abstract:

Despite the endemic characteristic of anaplasmosis in Venezuela, there have been few studies that refer to cross protection among distinct Venezuelan isolates of Anaplasma marginale. The objective of this work was to evaluate the development of this illness in crossbred-Holstein calves naturally infected with the Lara isolate and then challenged by homologous and heterologous isolates of rickettsia in search of cross protection. In order to achieve this purpose, crossbred-Holstein calves of one week of age, naturally infected with Anaplasma marginale, were acquired from a farm in Lara State and then divided into three groups of three animals each. After six months, they were inoculated with 5 × 108 erythrocytes infected with A. marginale homologous Lara isolate (group 1), heterologous isolates Tachira (group 2) and Zulia (group 3). From the beginning of experiment trials, blood samples were taken to evaluate parasitaemia and packed cell volume, as well as clinical signs were checked. The three groups were different in relation to the pre-patent period, levels of packed cell volume and parasitaemia after challenge. Two of three group 1 animals were protected against homologous challenge when they did not manifest signs of the disease, while the animals in groups 2 and 3 presented clinical evidence of anaplasmosis. The group inoculated with Zulia isolate showed a higher clinical severity than the group inoculated with Tachira isolate.