What do we really know about brucellosis diagnosis in livestock worldwide? A systematic review

Diagnosis of brucellosis is not a straightforward task, with over 40 different tests available. Accurate diagnosis requires a series of diagnostic testing with proper interpretation of results. The World Organization for Animal Health (WOAH) provides guidelines describing the different assays including their recommended use, protocols, and interpretation. PubMed, Embase and Web of Science databases were searched without restrictions and original work describing cross-sectional studies focusing on livestock species (cattle, buffaloes, sheep, goats and swine) were included while reviews, case reports, and case-control studies were excluded. In this study, we systematically reviewed the literature and critically assessed the findings from 349 research studies to provide an overview of the different diagnostic methods used worldwide in livestock, and compared the tools and strategies used against the WOAH recommendations. A total of 232 studies (66.5%) focused on cattle followed by goats (34.1%), sheep (31.5%), buffaloes (14.6%), and swine (5.2%). Of these studies, 171 were from Africa (48.9%), 132 from Asia (37.8%), 36 from the Americas (10.3%), and 10 from Europe (2.8%). The most utilized immunological assayswere Rose Bengal test and indirect ELISA (63.9 and 36.7%, respectively). Interestingly, 73 studies (20.9%) used a single immunological assay to report on the status of animals. Direct methods such as culture and PCR were performed in 100 studies (28.7%) with culture being the most utilized (19.8%). Strikingly, we found that only 16% of included studies followed WOAH recommendations in terms of sample chosen, diagnostic assay utilized, protocol employed and results interpretation. In countries that reported the presence of B. abortus, B. melitensis, and B. suis to the WOAH, only 4 of 28, 2 of 19, and 1 of 6 countries (reporting these strains, respectively), contained studies that followed guidelines and confirmed the presence of the pathogen. This highlights, not only significant gaps in currently available literature leading to an inaccurate picture of brucellosis in livestock, but most importantly raises significant issues regarding the accuracy of data reported by countries. These findings are concerning due to the significant consequences of not adhering to these guidelines including inaccurate diagnosis, delayed disease control, and increased zoonotic risk for exposed individuals.