zoonoses and communicable diseases common to ... - PAHO/WHO

BRUCELLOSIS 59complement fixation test is considered superior to the agglutination test, especiallyin herds vaccinated with B. melitensis Rev. 1, where agglutinating antibodies persistfor long periods. The 2-mercaptoethanol test has also given very good results in vaccinatedflocks. The results from the buffered-acid antigen (rose bengal) test arepromising, but experience with it is limited and definitive conclusions cannot bedrawn at this time. The ELISA test is the most promising.In diagnosing infections caused by B. melitensis in sheep, the Coombs’ test(antiglobulin test) modified by Hajdu can reveal 70% of infected animals. The othertests (agglutination, complement fixation) give less satisfactory results. In using theagglutination and complement fixation tests, adoption of significant titer levelslower than those for other animal species is recommended. Counterimmunoelectrophoresiswould detect antibodies against intracellular antigens that appear late in theserum but which remain a long time. Consequently, its use would be appropriate forsheep with chronic brucellosis that test negative by agglutination, rose bengal, andcomplement fixation (Trap and Gaumont, 1982). Experts agree that the diagnosticmethods for brucellosis caused by B. melitensis in goats and sheep leave much to bedesired and that more attention should be given to this problem given its publichealth importance.In diagnosing ram epididymitis caused by B. ovis, antigen prepared with thisagent must be used. The preferred tests are gel diffusion, complement fixation, andELISA. A study conducted in Australia in flocks infected by B. ovis and flocks freeof infection showed that this enzyme immunoassay detected more reactive animalsand that the complement fixation test failed to detect some rams that excreted B.ovis. In infection-free flocks, both ELISA and CF produced false positives at a rateof 0.5% (Lee et al., 1985). Bacteriologic examination of semen is an appropriatediagnostic method, but it should be kept in mind that the shedding of brucellae canbe intermittent.For dogs infected by B. canis, the surest diagnostic method is isolation of the etiologicagent from blood, vaginal discharges, milk, or semen, or from fetal tissue andplacenta. Bacteremia can last from one to two years, but after the initial phase it maybecome intermittent; thus, a negative blood culture does not exclude the possibilityof brucellosis.The most common serologic tests are plate and tube agglutination using B. canisantigen, immunodiffusion in agar gel with antigens extracted from the cell wall, 2-mercaptoethanol plate agglutination, and the modified 2 ME tube agglutination test.Possibly the most specific test to date, but also the least sensitive, is the immunodiffusiontest in agar gel that utilizes antigens extracted from the cytoplasm of B.canis. To a greater or lesser degree, all these tests give nonspecific reactions. Zohaand Carmichael (1982) showed that the immunodiffusion test using sonicated antigens(internal cellular antigens) is satisfactory shortly after the onset of bacteremiaand can detect infected animals for up to six months after it disappears, i.e., whenother tests give equivocal results. A new test has been developed that uses a nonmucoid(M–) variant of B. canis as the antigen in tube agglutination, after treatingthe sera with 2 ME. The test is more specific without reducing sensitivity(Carmichael and Joubert, 1987).Control: The most rational approach for preventing human brucellosis is the controland elimination of the infection in animal reservoirs, as has been demonstrated