Vaccination of pregnant ewes against infection with Salmonella Brandenburg.
OBJECTIVE
To develop a challenge model for Salmonella Brandenburg infection in pregnant ewes. To compare efficacies of a live attenuated Salmonella Typhimurium mutant, a subunit preparation from a virulent S. Brandenburg isolate, and a commercial multivalent inactivated vaccine in their ability to prevent experimental S. Brandenburg infection. To assess the efficacy of the live attenuated S. Typhimurium mutant against natural S. Brandenburg infection in lambs.


METHODS
Two-year-old ewes were immunised with either a live attenuated vaccine (eye-drop; n=20), a subunit vaccine (n=20) or an inactivated bacterin vaccine (n=20), both administered subcutaneously, or served as unvaccinated controls (n=21). Four weeks later, the sensitising regime was repeated as a booster vaccination, and the ewes were challenged 6 weeks later with a virulent S. Brandenburg isolate, approximately 6 weeks prior to lambing. The presence of clinical signs, abortion or death was noted following challenge. The presence and number of Salmonella spp in faecal samples taken throughout the trial, and in organs collected post mortem, were determined using an enrichment selection procedure, and confirmed by serology and pulsed-field gel electrophoresis (PFGE). Half of the surviving lambs were vaccinated with the live attenuated vaccine and all (n=39) were exposed to natural infection from contaminated pasture.


RESULTS
There was no significant protection against mortality and abortion following vaccination with the live attenuated, subunit and inactivated vaccines following experimental challenge with S. Brandenburg. There was a significant but transient decrease in the number of ewes shedding S. Brandenburg (live attenuated, p=0.05; subunit, p=0.05; inactivated, p=0.01), and in the quantity of these bacteria in the sheep from the vaccinated groups (p<0.05) compared with controls, 6 weeks after challenge. Lambs from the challenged ewes did not shed Salmonella spp after being vaccinated with the live attenuated vaccine, in contrast to some of the controls, when grazed on pasture contaminated with S. Brandenburg.


CONCLUSIONS
The use of live attenuated, subunit and inactivated vaccines did not significantly protect sheep against lethal experimental challenge with S. Brandenburg.
Li
H
H
Agriculture and Life Sciences Division, Lincoln University, PO Box 84, Lincoln, New Zealand.
McFarlane
R G
RG
Wagner
J
J
D000034:Abortion, Veterinary / Q000382:microbiology; D000818:Animals; D001428:Bacterial Vaccines / Q000008:administration & dosage*; D005243:Feces / Q000382:microbiology; D005260:Female; D007114:Immunization / Q000662:veterinary; D007279:Injections, Subcutaneous / Q000662:veterinary; D011247:Pregnancy; D012481:Salmonella Infections, Animal / Q000401:mortality / Q000517:prevention & control*; D019779:Salmonella enterica / Q000276:immunology*; D012756:Sheep; D012757:Sheep Diseases / Q000401:mortality / Q000517:prevention & control*; D014613:Vaccines, Attenuated / Q000008:administration & dosage*; D022223:Vaccines, Subunit; D014774:Virulence
D001428:Bacterial Vaccines; D014613:Vaccines, Attenuated; D022223:Vaccines, Subunit