Global Human Brucellosis Incidence

Background: For decades, human brucellosis has been recognized worldwide as a significant cause of morbidity, yet the annual incidence of this disease remains unknown. We analyzed this frequency, using international reports (2005–2019), identifying information gaps, and distinguishing a possible path forward. Methodology/Principal findings: A novel approach to estimating the incidence of this disease was explored. We utilized annual health data extracted from the World Organization for Animal Health (OIE)–World Animal Health Information System (WAHIS) database, assessing the dataset completeness and representativeness of the data for the world population. Additionally, we assessed the reported country level human brucellosis case counts and the factors that influenced the observed changes over time. Our analysis revealed incomplete and unrepresentative information, preventing the estimation of annual human brucellosis case incidence at the global level. In the OIE-WAHIS database, only 48.4% of the required reports have been submitted as of 2019, with approximately 47.3% of the world population represented. Additionally, geographic regions were disproportionate in completeness, representativeness, and actual reported case counts. Africa and Asia constituted the majority of reported cases, while simultaneously submitting the lowest percentage of reports as well as covering the lowest percentage of their populations within those reports, when compared to the rest of the world. Conclusions/Significance: The global annual frequency of human brucellosis cases remains elusive. Furthermore, there exists great heterogeneity in diagnostic, surveillance, and reporting systems worldwide, calling into question the validity of available information. This study reveals that the Neglected Zoonotic Disease priority status for brucellosis should be restored.

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.

Brucellosis is a neglected and re-emerging zoonotic disease of nearly worldwide distribution. Recently, a new model utilizing publicly available data, voluntarily provided by countries to the World Organization for Animal Health (WOAH), estimated a global annual incidence of at least 1.62–2.10 million cases. However, global and regional knowledge gaps, partially attributed to lack of diagnostic capability and disease unawareness, result in misdiagnosis. This study incorporated misdiagnosis to assess the potential impact on incidence estimates. Specifically, we examined the potential impact of misdiagnosing brucellosis as malaria. Incidence rates modeled from WOAH data comprised a baseline estimate for brucellosis rates. A range of potential misdiagnosis rates based on World Bank malaria data and scientific literature were utilized to estimate the number of misdiagnosed cases. We assumed a conservative misdiagnosis range of 0.25-4.00% based on clinical studies that reported a 4–11% misdiagnosis rate. We show that malaria misdiagnosis can significantly impact global annual incidence estimation of brucellosis. Rates of 0.25% increase brucellosis incidence by 0.34-5.4 M cases, while rates of 4% increase these estimates by 2.43-7.45 M cases. Human brucellosis misdiagnosed as malaria can significantly impact global annual incidence estimates. Enhanced efforts are needed to identify misdiagnosed cases in countries where both diseases are endemic.

Brucellosis is a zoonotic disease known to be endemic to parts of western and sub-Saharan Africa. However, the epidemiology for humans and animals remains largely unknown in many of these countries with Cameroon being a typical example. Despite common knowledge that brucellosis affects livestock, the actual number of infected animals remains unknown. Through a scoping review, the current known status of the disease is described. The aim is to ascertain relevant and publicly accessible research and knowledge of human and animal brucellosis in the country, and to provide an overview of the factors associated with its known persistence. Seroprevalence has been estimated and published in 12 separate instances (1 human; 9 cattle; 1 human and cattle; and 1 that includes cattle, pigs, and small ruminants), between 1982 and 2020, in 9 of the country’s 10 geopolitical regions. In 1983, Brucella abortus and B. melitensis were isolated in cattle, but no further bacterial isolation has been published since. The seroprevalence from 196 total humans has ranged between 5.6% and 28.1%, and between 3.0% and 30.8% for 14,044 total cattle. As there is no ongoing surveillance program, it is not currently possible to identify the specific Brucella spp. that are endemic to the country and its regions. There are sufficient agricultural systems of cattle, pigs, goats, and sheep to sustain the presence of multiple Brucella spp. Surveillance information is the cornerstone of epidemiologic decision making, and is needed to direct policy makers, public health authorities, and veterinary services to appropriate actions. A combination of serological and molecular based diagnostics for surveillance is necessary to identify, quantify, and direct the appropriate public health interventions. Cameroon has an opportunity to build public and animal health infrastructure, leading the way for central Africa in the management and future eradication of brucellosis.

Brucellosis is a neglected zoonotic disease impacting agricultural economies, as well as animal and human health globally. In sub-Saharan Africa, brucellosis is considered endemic in many countries based on serological evidence, although the presence and distribution of specific Brucella species remain unverified due to limited bacteriological confirmation. Due to the economic importance and national/international trade routes, this cross-sectional study investigates Brucella prevalence in 4612 animals (cattle, sheep, goats, and pigs) from slaughterhouses in the Far-North, North, and West regions of Cameroon sampled between February 2021 and May 2023. The analysis includes serology (Rose Bengal Test and indirect Enzyme-Linked Immunosorbent Assay), culture, real-time PCR, and next-generation sequencing (NGS). Results show only Brucella abortus is present, primarily affecting cattle (8.3%) and goats (7.3%). NGS reveals the local B. abortus strain is related to the clade from Uganda and Sudan, indicating it is endemic to Africa, rather than introduced from outside the continent. These results confirm the presence of a genetically distinct African lineage and reinforce brucellosis as a major concern for both animal and public health. The study emphasizes the critical need for coordinated surveillance systems to support evidence-based control strategies, enhance disease monitoring, and reduce the risk of transboundary transmission.