[Immune response and reproductive consequences in experimentally infected ewes with Brucella ovis during late pregnancy]. / Respuesta humoral y consecuencias reproductivas en ovejas desafiadas con Brucella ovis al final de la gestación.

ABSTRACT

Ovine brucellosis by Brucella ovis is a highly prevalent disease in Argentina. This study aimed to evaluate the pathogenicity of B. ovis and the serological response in ewes during late pregnancy and in their offspring. Six adult ewes were distributed in two groupsG1 (pregnant females, n = 4) and G2 (nonpregnant females, n = 2). Three pregnant ewes at 15 days prepartum and one nonpregnant eve were inoculated with B. ovis. Sera of sheep and their offspring were analyzed by different serological tests. Samples of cervicovaginal mucus, placenta and milk were studied by bacteriology. A Brucella genus-specific PCR assay was carried out in placenta and milk samples. Placenta samples were hystopathologically processed. g1 females gave birth to live lambs, but one died hours postpartum. Serological techniques employed detected antibodies in serum of inoculated pregnant animal 5 days postchallenge. sera of female controls G1 and G2 remained negative throughout the study. Cervicovaginal mucus of infected ewes in G1 and G2 yielded negative results to bacteriology, but B. ovis was isolated from milk. The PCR assay was positive for the placenta and milk from inoculated pregnant ewes. Histopathology revealed necrotic suppurative placentitis in one placenta. However, although results demonstrated that B. ovis can invade the placenta and mammary gland, this bacterium did not cause abortion when it was inoculated intravenously at 15 days prepartum. B. ovis infection induced an early humoral response in pregnant ewes, but their lambs remained seronegative, indicating that there was no transfer of antibodies in infancy. Placenta colonization and milk excretion of B. ovis involves a potential source of infection for lambs, which could play a role as latent carriers of infection.