THE EFFICACY OF A LIVE LISTERIA-MONOCYTOG ENES VACCINE CONTAINING SEROTYPE-1 2A AND SEROTYPE-4B IN SHEEP/

In two experiments, sheep and lambs were vaccinated subcutaneously wit h a vaccine containing live serotypes 1/2a and 4b of Listeria monocyto genes and challenged 16 days later with a mixture of homologous wild s trains. The mortality rate of vaccinated sheep was 28.1% and that of c ontrols 71.9%; 25% of lambs died. In addition, two field trials were c onducted in listeria infected flocks in which primiparous pregnant ewe s were vaccinated. In the first, 3 lambs, born of 564 vaccinated ewes, died of listeriosis compared with 110 born of 3345 unvaccinated ewes. In the second, the perinatal mortality rate of lambs born of vaccinat ed ewes was offspring of control ewes and the mean birth weights were 2.2 and 1.8 kg, respectively. The mean milk yields were 106 l and 83 l . Listeria was not isolated from milk samples from vaccinated ewes, wh ilst 31,9% of milk from controls yielded Listeria. It was concluded th at the vaccine is efficacious in sheep.