Trypanosomiasis by Trypanosoma vivax in cattle in the Brazilian semiarid: Description of an outbreak and lesions in the nervous system.

An outbreak of trypanosomiasis by Trypanosoma vivax is reported in the semiarid of Paraíba, Northeastern Brazil from May to August 2002. Sixty-four cows out of 130 were affected; 11 died and the other recovered after treatment with diminazene aceturate. Affected animals had fever, anemia, weight loss, hypoglycemia, increased serum levels of aspartate aminotransferase and, in nine cows, nervous signs. All cows with nervous signs died; six of them recovered after treatment, but the disease relapsed. Six cows aborted and one delivered a calf that died immediately after parturition. Thirty-two out of 100 calves were affected and five died. Nervous signs were not observed in the calves. Gross lesions were thickening of the meninges, enlarged lymph nodes and prominent white pulp of the spleen. The main histological lesion was meningoencephalitis and malacia in the brain of cows with nervous signs. No antibodies against trypanosomes were found in 33 blood samples collected before the outbreak in the affected farm and in 29 samples collected at the same time in two other neighbor farms. Until January 2003, all 89 animals tested had antibodies against T. vivax, suggesting the occurrence of sub clinical infections in cattle without clinical signs. Only two out of 85 serum samples collected on April 2004 were positive for T. vivax antibodies. Data obtained suggested that the semiarid region is non-endemic for trypanosomiasis and that disease occurred due to introduction of the parasite in a susceptible population after an apparent rise in the Tabanus spp. population.