Epidemiology of babesiosis and anaplasmosis in South and Central America

Babesiosis (Babesia bovis and Babesia bigemina) and anaplasmosis (Anaplasma marginale) affect native cattle from Uruguay and northern Argentina to Guatemala. The distribution of Babesia follows the dissemination of the tick vector. Seroepidemiological studies showed that enzootic instability exist in herds in several areas of the region. However, clinical cases occurred less frequently than expected. The babesial tick infection rate is related to the vector abundance which in turn is regulated by climate. Bos indicus cattle, because of tick resistance, are less likely to be infected by the vector. This can result in herd instability, but clinically is partly compensated by the resistance of Bos indicus and their crosses to babesiosis. Excessive use of acaricides and rotational grazing appears to be related to outbreaks of babesiosis especially in dairy cattle. Factors involved in the epidemiology and transmission of anaplasmosis are not well defined. The role of ticks, haematophagous diptera, iatrogenic and intrauterine transmissions needs to be investigated under local conditions. Therefore, the knowledge of this disease is meager. Utilization of biotechnological methods may help in obtaining information on Babesia-Boophilus-Bos relationship and on the transmission of A. marginale.

Identification of two Th1 cell epitopes on the Babesia bovis-encoded 77-kilodalton merozoite protein (Bb-1) by use of truncated recombinant fusion proteins

Previous studies have demonstrated the serologic and T-cell immunogenicity for cattle of a recombinant form of the apical complex-associated 77-kDa merozite protein of Babesia bovis, designated Bb-1. The present study characterizes the immunogenic epitopes of the Bb-1 protein. A series of recombinant truncated fusion proteins spanning the majority of the Bb-1 protein were expressed in Escherichia coli, and their reactivities with bovine peripheral blood mononuclear cells and T-cell clones derived from B. bovis-immune cattle and with rabbit antibodies were determined. Lymphocytes from two immune cattle were preferentially stimulated by the N-terminal half of the Bb-1 protein (amino acids 23 to 266, termed Bb-1A), localizing the T-cell epitopes to the Bb-1A portion of the molecule. CD4+ T-cell clones derived by stimulation with the intact Bb-1 fusion protein were used to identify two T-cell epitopes in the Bb-1A protein, consisting of amino acids SVVLLSAFSGN VWANEAEVSQVVK and FSDVDKTKSTEKT (residues 23 to 46 and 82 to 94). In contrast, rabbit antiserum raised against the intact fusion protein reacted only with the C-terminal half of the protein (amino acids 267 to 499, termed Bb-1B), which contained 28 tandem repeats of the tetrapeptide PAEK or PAET. Biological assays and Northern (RNA) blot analyses for cytokines revealed that following activation with concanavalin A, T-cell clones reactive against the two Bb-1A epitopes produced interleukin-2, gamma interferon, and tumor necrosis factors beta and alpha, but not interleukin-4, suggesting that the Bb-1 antigen preferentially stimulates the Th1 subset of CD4+ T cells in cattle. The studies described here report for the first time the characterization, by cytokine production, of the Th1 subset of bovine T cells and show that, as in mice, protozoal antigens can induce Th1 cells in ruminants. This first demonstration of B. bovis-encoded Th1 cell epitopes provides a rationale for incorporation of all or part of the Bb-1 protein into a recombinant vaccine.