Imunological aspects inthe diagnosis and control of contagious epidymitis of rams by Brucella ovis

Abstract

Brucella ovis is the aethiological agent of ram contagious epididymitis, an infectious disease causing reproductive failure in sheep. Control measures include elimination of rams found positive in serological tests and/or bacteriological culture of semen, and vaccination when the prevalence is high.

The principal vaccine used against ovine brucellosis is B. melitensis Rev. 1, a live attenuated strain of B. melitensis. However Rev. 1 evokes antibodies interfering with the interpretation of serological tests used to diagnose infection by B. ovis and B. melitensis.

B. ovis is a natural rough species so lacks O polisaccharide chain. The outer membrane proteins of B.ovis have been studied by several groups searching for antigens useful for diagnosis and protection. A hot saline extract fron B. ovis contains rough lipopolysaccharide and several proteins, including abundant group 3 outer membrane proteins

The most efficient and widely used tests for serodiagnosis of B. ovis infection are double gel diffusion, complement fixation test and ELISA. Hot saline extract has provided best diagnostic results in all tests. However some cross-reactivity in these tests can be seen with sera of sheep naturally infected with B. melitensis or after B. melitensis Rev. 1 vaccination. Less information is available on internal B. ovis antigens. Recently, an indirect ELISA using BP26 (periplasmic protein) has been developed for the differentiation of infected and vaccinated rams.

The identification of B. ovis antigens able to elicit a protective immune response is of great interest for the development of subcellular vaccines avoiding the drawbacks of living attenuated vaccine. In the mouse model, passive protection experiments with mixtures of anti-outer membrane proteins and rough lipopolysaccharide monoclonal antibodies have shown to protect against B. ovis infection.