Vaccination of pregnant ewes against infection with Salmonella Brandenburg

Authors: Wagner J, Li H, McFarlane RG
Publication: New Zealand Veterinary Journal, Volume 53, Issue 6, pp 416-422, Dec 2005
Publisher: Taylor and Francis

Animal type: Livestock, Production animal, Ruminant, Sheep
Subject Terms: Abortion/stillbirth, Animal remedies/veterinary medicines, Bacterial, Biosecurity, Disease control/eradication, Epidemiology, Reproduction, Alimentary system/gastroenterology, Immune system/immunology, Mortality/morbidity, Notifiable organisms/exotic disease, Pregnancy, Reproduction - female, Disease/defect, Infectious disease, Vaccination, Zoonosis, Public health
Article class: Scientific Article

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Abstract: AIMS: 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.
KEY WORDS: Salmonella enterica Brandenburg, mortality, abortion, bacterial shedding, vaccine, pregnant ewes

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