The Value of Serologic Tests for Diagnosis and Follow up of Patients having Brucellosis

Abstract

Though diagnosis of human brucellosis is accurate when the causal agent is isolated, this procedure is not always successful and the most of patients are diagnosed on the basis of rising titres of antibodies in serum. The classical tests used for detection of antibodies to S-Brucella sp., include Rose Bengal (RBT), buffered plate antigen (BPAT), serum agglutination (SAT), 2-mercapto-ethanol (2MET) and complement fixation (CFT). The modern methods are based on primary binding assays of which a competitive enzyme immunoassay (CELISA) and fluorescence polarization (FPA) are the best developed. For antibodies to R-Brucella sp. a rapid slide agglutination (RSAT) as screening and an indirect ELISA (IELISA) as confirmatory tests have been reported. We have selected 23 cases of human brucellosis that were followed up over a long period, to assess which test was most effective in detecting different stages of the disease. The patients were divided into five groups: "chronic" cases; relapses; infection acquired in a laboratory; patients presumptively infected with B. canis and cases with a long history of brucellosis. The results suggest that BPAT is a practical test that reduces non specific reactions and is more sensitive than RBT. SAT detects the acute form but cross reacts with other antibodies and the diagnostic end-point titre has not been satisfactorily established; 2MET should be discontinued because of its toxicity and the scant information it can add; CFT fails to detect the acute form and is technically complicated. CELISA correlate well with the clinical course and is useful to detect acute as well as "chronic" cases and FPA do not work in serum with high lipid content. RSAT and IELISA are useful tests for brucellosis caused by B. canis. A unique protocol for serologic diagnosis that uses robust tests would be of value to the surveillance and control the disease.