Evaluation of an In-house Indirect ELISA for Differential Detection of IgM and IgG anti-Brucella Antibodies in Human Brucellosis

Brucellosis caused by various species of the genus Brucella is one of the most important zoonotic diseases of global importance with veterinary, public health, and economic concerns. The study aimed to standardize IgM and IgG-based iELISA to detect anti-Brucella antibodies for serodiagnosis of acute and chronic human brucellosis. The test was standardized using 1:320 dilution of smooth lipopolysaccharide (sLPS) antigen from B. abortus S99 strain, 1:80 serum dilution, 1:4000 anti-human IgM and IgG conjugates, respectively for both IgM and IgG iELISA. The cut-off using 50 each brucellosis positive and negative human sera panel samples was set at ≥ 42 for both IgM and IgG iELISA. A total of 700 human sera samples were evaluated (137 veterinary doctors, 157 artificial inseminators, and 406 veterinary assistants). Overall, the study detected 8.3%, 8.1%, 8%, and 6.1% positivity by in-house IgG iELISA, RBPT, IgM iELISA, and SAT tests, respectively. Considering commercial iELISA kit as a gold standard, the sensitivities of IgM and IgG iELISA were 90% and 97.9%, respectively, whereas, specificities were >99%. The study established >98% specificity and >90% sensitivity for differential detection of immunoglobulin classes in the standardized iELISA. The developed assay outperformed the other evaluated tests with a shorter assay time and can be implemented in both endemic and non-endemic regions for surveillance and diagnosis of human brucellosis.