The Rose Bengal Test in Human Brucellosis: A Neglected Test for the Diagnosis of a Neglected Disease

Brucellosis is a highly contagious zoonosis affecting livestock and human beings. The human disease lacks pathognomonic symptoms and laboratory tests are essential for its diagnosis. However, most tests are difficult to implement in the areas and countries were brucellosis is endemic. Here, we compared the simple and cheap Rose Bengal Test (RBT) with serum agglutination, Coombs, competitive ELISA, Brucellacapt, lateral flow immunochromatography for IgM and IgG detection and immunoprecipitation with Brucella proteins. We tested 208 sera from patients with brucellosis proved by bacteriological isolation, 20 contacts with no brucellosis, and 1559 sera of persons with no recent contact or brucellosis symptoms. RBT was highly sensitive in acute and long evolution brucellosis cases and this related to its ability to detect IgM, IgG and IgA, to the absence of prozones, and to the agglutinating activity of blocking IgA at the pH of the test. RBT was also highly specific in the sera of persons with no contact with Brucella. No test in this study outperformed RBT, and none was fully satisfactory in distinguishing contacts from infected patients. When modified to test serum dilutions, a diagnostic titer >4 in RBT resulted in 87.4% sensitivity (infected patients) and 100% specificity (contacts). We discuss the limitations of serological tests in the diagnosis of human brucellosis, particularly in the more chronic forms, and conclude that simplicity and affordability of RBT make it close to the ideal test for small and understaffed hospitals and laboratories.
Author Summary The Rose Bengal Test (RBT) for brucellosis serological diagnosis was adapted to test serum dilutions and its usefulness evaluated using sera of Brucella culture positive patients, persons with contact with Brucella but no symptoms, veterinarians accidentally injected with vaccine Rev 1 who had not developed the disease and normal persons. Using the standard protocol, RBT was not outperformed by more sophisticated and expensive tests (serum agglutination, Coombs, competitive ELISA, Brucellacapt, and lateral flow immunochromatography for IgM and IgG detection) in identifying Brucella infected patients. All tests failed to discriminate with total specificity the sera from contacts or Rev 1 injected individuals. However, none of these sera was positive in the modified RBT adapted to test serum dilutions at titers higher than 1>4. When there is suspicion of brucellosis, RBT is recommended as the first test and, depending upon the titer, a positive result does not need confirmation by other (usually more expensive, sophisticated and time consuming) tests.