Bovine Trypanosomiasis in Brazil

Abstract

Trypanosoma vivax significantly impacts the livestock systems, since it affects animals of economic importance, such as ruminants. It causes disease not only in cattle but also in buffaloes, and it is able to infect a large number of both domestic and wild species. Based on the way the parasite is transmitted to the host, the genus Trypanosoma is classified into two groups: Salivaria and Stercoraria. T. vivax is mainly transmitted in a cyclic manner by the tsetse fly bite in areas where this vector is present. In the American continent, due to the absence of the vector, the parasite has adapted to the mechanical transmission, via bloodsucking insects such as Stomoxys calcitrans and tabanids. In cattle, the incubation period ranges from 9 to 14 days, for virulent isolates, and 9–59 days for the less pathogenic isolates. The main clinical signs of the infection are fever, anemia, miscarriage, appetite loss, lethargy, progressive weight loss, and dysentery. The disease can be controlled by chemical treatment, particularly during early periods of acute disease. However, in cattle with neurological symptoms, the treatment is not efficient because there is recurrence of the disease and death of the animals. Clinical and parasitological relapses observed after the treatment of animals with nervous signs have been associated with the presence of the parasite in the nervous tissue, cerebrospinal fluid, and aqueous humor, where trypanosomes are protected against trypanocidal drugs. The growing incidence of resistance to drugs has complicated the treatment and control of trypanosomiasis in recent times.