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

Abstract

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.

Fig 1. PRISMA flow diagram for the selection of the studies analyzed.

Fig 2. Temporal distribution and frequency of included studies by 5 years intervals from 1979 to 2023.

(A) Overall temporal distribution. (B) Temporal distribution by livestock species studied.

Fig 3. Geographical distribution, area characteristics (urban or rural) and socioeconomic status.

(A) Geographical distribution of the selected studies focusing on the diagnosis of brucellosis in livestock. Colored countries were included in the study. The map was created using mapchart.net and the basemap is available at: https://www.mapchart.net/world.html. (B) Repartition of the selected studies by continent and subregion. (C) Country classification based on the area characteristic of the sampled region. (D) Distribution of countries by socioeconomic status.

Fig 4. Adherence of studies to WOAH guidelines by socioeconomic status and continent.

Sample type, choice of diagnostics tests, applied protocols, and interpretation of results were determined and subsequently classified into 3 groups: 1) Insufficient information (critical information missing that did not allow for a conclusion), 2) Not in accordance (one or several of the mentioned parameters were not in accordance with WOAH recommendations), or 3) In accordance (all of the mentioned parameters were in accordance with WOAH recommendations). (A) Overall classification of studies based on accordance to guidelines. (B) Classification of studies based on accordance to guidelines and socioeconomic status. (C) Classification of studies based on accordance to guidelines and geographical region.

Fig 5. Geographical representation of the presence or absence of the major zoonotic species of Brucella as reported to the WOAH.

(A) Presence or absence of B. abortus, (B) B. melitensis, and (C) B. suis. Countries considered disease free are labeled in green, while those that are considered endemic are labelled in red. Countries that do not report any information are labelled in dark gray. Countries in light grey were not included in this analysis. The maps were created using mapchart.net and the basemap is available at: https://www.mapchart.net/world.html.