Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 5, 1996
Publication Date: N/A
Interpretive Summary: Brucellosis is a disease of cattle which causes pregnant cattle to abort or miscarry thus losing their calf. A vaccine called RB51 has been developed to protect cattle against brucellosis. In order to test its safety in pregnant cattle, cows 6 months pregnant were injected with RB51. It was found that none of the cattle aborted, however, one calf was born prematurely and was weak, unable to stand, and infected with the vaccine RB51. All but two of the remaining cattle in the experiment had inflammation of the placenta and uterus and numerous organs including the placenta and uterus were infected with RB51. It is shown by this study that RB51 can infect the placenta and fetus in a pregnant cow, however, it did not cause abortion. The premature delivery of one calf does suggest that further studies in pregnant cattle are warranted.
Technical Abstract: To determine placental tropism and abortigenicity of the vaccine candidate, B. abortus strain RB51, a rough mutant of the virulent strain 2308, 10 Polled Hereford heifers were inoculated intravenously in the sixth month of gestation. Heifers were examined at 8 weeks p.i.(n=5) or at full term (n=5). Four of five heifers at 8 weeks p.i. and 3/4 heifers at term had placentitis. Trophoblastic epithelium of the placentomal arcade zone had abundant intracytoplasmic bacteria that were immunoreactive for RB51 antigen. Tips of maternal septae had a lymphoplasmacytic infiltrate with multifocal erosions and ulcerations of epithelium. RB51 was cultured from all tissues in which lesions were seen. Placentae of one cow from each group had no placentitis and were culture negative for RB51. Four of five fetuses at 8 weeks p.i. and 3/4 full term calves had RB51 in liver, spleen , lung and bronchial lymph nodes but no lesions were seen. One heifer in the full term group delivered a premature weak fetus. The dam had severe placentitis and lymphoplasmacytic endometritis. All tissues and fluids sampled from the heifer and calf contained RB51. These results establish that B. abortus strain RB51 can infect the bovine placenta and fetus and can induce placentitis which in some cases can lead to preterm labor.