A review on diagnostic techniques for brucellosis

Brucellosis presents with many clinical manifestation that make its diagnosis a difficult task. Ever since the report of the first serologic test for brucellosis, a definitive diagnostic technique has been actively pursued. The most widely used methods of diagnosis are based on serology, which measures the ability of the serum (antibody) to agglutinate a standardised amount of killed Brucella abortus (antigen) containing O-side chain. These tests are most commonly used because they are safe. However, they are prone to false-positive results due to other cross-reacting bacteria, and also, they are not useful in the detection of Brucella canis and Brucella ovis which lack the O-side chain. Other useful tests include the direct smear examination which is a presumptive method that involves making smears from vaginal swabs, placentas or aborted foetuses, stained with the stamp modification of the Ziehl-Neelsen method. Morphologically related micro-organisms such as Chlamydia psittasi, Chlamydophila abortus or Coxiella burnetti can mislead the diagnosis, therefore, confirmation on appropriate culture and selective media is recommended. Culture and isolation of the organism from blood or tissue samples has remained the only “unequivocal” method but lacks sensitivity, and its outcome depends on individual laboratory practices, and how actively the obtaining of cultures is pursued. Laboratory animal inoculation has also been a useful tool, but is also subject to interference with gastric acids. More recently, the polymerase chain reaction (PCR) has been found to be a useful and more sensitive test, but has not been validated for standard laboratory use. This paper highlights useful samples and, especially the different conventional to more sophisticated molecular techniques for the diagnosis of brucellosis.