Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/1996
Publication Date: N/A
Interpretive Summary: Brucellosis is an economically important disease of cattle resulting in abortion and decreased production. The vaccine, Brucella abortus strain SRB51 has recently been approved as a vaccine for calves, however, the use of strain RB51 in pregnant cattle remains experimental. Previous work with intravenous vaccination of pregnant cattle with high doses of strain RB51 showed that strain RB51 can infect the placenta and fetus, although abortion did not occur. This experiment was designed to determine the effects of subcutaneous vaccination of lower doses of strain RB51 on pregnant cattle. Subcutaneous vaccination of cattle at six months of pregnancy with strain RB51 did not result in abortion, fetal infection or widespread maternal infection. Eight to ten weeks later, at full term of pregnancy, strain RB51 was only recovered from lymph nodes located in the region of vaccination. Assays to determine immune responses of pregnant cattle showed that immune responses greater than those seen in non-vaccina ttle were induced in pregnant cattle vaccinated with strain RB51. This information on the safety of strain RB51 in pregnant cattle will be useful to animal health officials, veterinarians and cattle producers faced with a brucellosis outbreak where all female cattle should be vaccinated including pregnant cattle.
Technical Abstract: Polled Hereford heifers were vaccinated subcutaneously at 6 months of ges n with 10(9) CFU SRB51 (n=5), 3 x 10(8) CFU S19 (n=5) or sterile saline (n=2). Signs of abortion, arthrit or anaphylaxis were not seen in either vaccine group and gross or microscopic consistent with brucellosis were not seen at necropsy of full term heifers. At necropsy, 2/5 SRB51-vaccinates still had SRB51 in superficial cervical lymph nodes draining the region of vaccination. Bacteriologic culture did not recover SRB51 or S19 from any other tissues or fluids from heifers or their calves. SRB51-vaccinates did not develop antibody titers detected by standard tube agglutination, but did develop titers greater (P<0.05) than S19-vaccinates on a dot ELISA which detects anti-SRB51 antibodies. Lymphocyte blastogenesis assays on maternal PBMC showed proliferative responses to irradiated SRB51 and irradiated S19 in SRB51- and S19-vaccinates which were greater (P<0.05) than that seen in saline-vaccinated controls. Lymph node cells from maternal superficial cervical lymph nodes of SRB51-vaccinates showed proliferation which was not different (P>0.05) from saline-vaccinated controls, however; lymph node cells from S19-vaccinates proliferated greater than lymph node cells from controls (P<0.05) in response to irradiated SRB51 or irradiated S19. These results support the use of SRB51 as a brucellosis vaccine in pregnant cattle, showing that pregnant cattle can be safely vaccinated subcutaneously with 10(9) CFU SRB51 without widespread maternal or fetal infection, placentitis or abortion, and that such vaccination is immunogenic in pregnant cattle inducing both humoral and cell-mediated responses.