BRUCELLA-MELITENSIS INFECTION IN SHEEP - PRESENT AND FUTURE

Sheep brucellosis, a zoonosis mainly due to B. melitensis (biovar 1, 2 or 3), remains widespread world-wide. Pathologically and epidemiologi cally, the disease is very similar to B. abortus infection in cattle. The live B. melitensis Rev 1 strain is currently considered as the bes t vaccine available for the control of sheep brucellosis, especially w hen used at the standard dose by the conjunctival route. Used exhausti vely in whole-flock vaccination programmes, it induces a great decreas e in the prevalence in both sheep and human populations. The expensive test-and-slaughter strategy should be restricted to the lowest infect ed areas. Whenever possible, Brucella spp. should be isolated by cultu re using adequate selective media from uterine discharges, aborted fet uses, udder secretions or selected tissues, such as lymph nodes, teste s or epididymides. Species and biovar identification is routinely base d on cultural criteria, on lysis by phages and on simple biochemical a nd serological tests. The recently developed polymerase chain reaction methods provide additional means of detection and identification. Des pite the high degree of DNA homology within the genus Brucella, severa l methods, including PCR-RFLP and Southern blot, have been developed w hich allow, to a certain extent, the differentiation between Brucella species and some of their biovars. While several ELISA tests have been developed recently, the rose bengal plate agglutination and complemen t fixation tests, based on the detection of anti-S-LPS antibody, are s till recommended for screening flocks and individuals. However, these tests sometimes lack specificity or sensitivity. For pooled samples, t here: are no useful tests such as the milk ring test in cattle. The br ucellin allergic skin test can be used as a screening or complementary test in unvaccinated flocks, provided that a purified, lipopolysaccha ride (LPS)-free and standardized antigen preparation is used. (C) Inra /Elsevier, Paris.