Immunization of Sheep Against Caseous Lymphadenitis

Abstract

The aim of this study was to evaluate the efficacy of various vaccines against caseous lymphadenitis in sheep. A culture of a local strain of Corynebacterium pseudotuberculosis CP41 N was produced using IBT bioreactor at pH 8, temperature 31 º C and dilution rate of 0.02 h­¹. The harvest was used to prepare five types of vaccines; The first was a killed whole cell vaccine containing 8mg bacterial dry weight / 0.5ml, the second was a  cell wall vaccine containing 3mg protein/ 0.5 ml,  the third was a toxoid vaccine containing 4 mg protein /0.5 ml, the fourth was the cell wall + the toxoid vaccine (3mg protein/ 0.5ml+ 4mg protein /0.5ml) and the fifth was the  killed whole cell + the toxoid vaccine (8mg bacterial dry weight /0.5ml + 4 mg protein/0.5ml). Saponin and aluminum hydroxide adjuvants were added in a concentration of 1mg/1ml dose each to the different vaccines. Each vaccine was injected subcutaneously in animals of one of 5 groups of sheep of 7 animals each, and animals in the sixth group were left as unvaccinated control. All animals were bled at weekly intervals for serological monitoring by the agglutination test. After four weeks, a booster dose of each vaccine as the 1st dose was given to the animals. Four weeks after the second dose of vaccine, all animals were challenged subcutaneously with 5.1X108 CFU of C. pseudotuberculosisCP41 N. The animals were then slaughtered four weeks later to determine the number of abscesses in the carcasses. The results showed that the vaccine which consisted of killed whole cells + the toxoid was the best of the five vaccines with a significant reduction (p<0.05) in mean abscess numbers in vaccinated animals after challenge with C. pseudotuberculosis. The percentage of protection of the group vaccinated with the killed whole cell+ the toxoid was 75% compared with  32.3%, 37.5%, 37.5% and 45.3% for the groups vaccinated with the cell wall lysate, the killed whole cell, the toxoid and the cell wall lysate + the toxoid vaccines,  respectively.