FURTHER-STUDIES OF THE APPLICATION OF LIVE SALMONELLA-ENTERITIDIS AROA VACCINES IN CHICKENS

A model was developed to simulate the lateral spread of Salmonella ent eritidis infection among chickens. One group of newly hatched chicks w as vaccinated orally with S enteritidis aroA. At three weeks old naive chickens were infected with a wild-type strain of S enteritidis and b rought into contact with separate groups of aroA vaccinated chickens a nd unvaccinated control chickens. The vaccinated chickens were well pr otected against colonisation of the gut by the wild-type strain wherea s the control group became heavily colonised. The IgG responses to a l ipopolysaccharide extract of S enteritidis in the vaccinated chickens indicated a limitation of invasion from the gut. Chickens vaccinated o rally at one day old with S enteritidis aroA were not protected agains t oral or intravenous challenge at eight weeks old with a wild-type st rain of S typhimurium. A group of newly hatched female chicks was vacc inated orally with S enteritidis aroA and again at two weeks old. A se cond group also received oral booster doses at 16 and 18 weeks. When c hallenged intravenously with a wild-type strain of S enteritidis at 23 weeks old there was a significant reduction in the numbers of this st rain in the spleens, livers, ovaries and caeca of both vaccinated grou ps. Booster vaccination at 16 and 18 weeks of age induced the greatest protection of the caeca.