Human Brucellosis: An Ongoing Global Health Challenge

Brucellosis is one of the most common zoonotic diseases, caused by species of the genus Brucella, that affects domestic and farm livestock and a wide range of wild mammals (1–2). Endemic areas are primarily located in the lowand middle-income countries across the Mediterranean region, the Arabian Peninsula, Africa, Asia, and Central and South America, with major regional differences (3–5). The highest prevalence in animals was observed in countries of the Middle East and sub-Saharan Africa, China, India, Peru, and Mexico (3,6–7). Only a few countries in the world are free from the infectious agent and are mainly in developed regions in Western and Northern Europe, Canada, Japan, Australia, and New Zealand (1). The human brucellosis, also known as undulant fever or Malta fever, was first recognized in Malta during the 1850s. The infection in humans is primarily caused by direct contact with infected cattle (Brucella abortus), sheep and goats (B. melitensis), pigs (B. suis), dogs (B. canis), or by ingesting unpasteurized and contaminated animal products. B. melitensis is the most common cause of reported human brucellosis cases and the most severe form of the disease (4). Human infections caused by inhaling airborne agents were also reported (8). In addition, because brucellosis is one of the most common laboratory-acquired infections, strict safety precautions should be followed when handling cultures and infected samples. Human brucellosis affects humans of all ages and sex and typically manifests as a variety of symptoms and signs including intermittent or irregular fever, headache, weakness, profuse sweating, chills, weight loss, and general aching. These non-specific clinical manifestations make it difficult to distinguish from other febrile conditions. However, if the disease is not diagnosed properly and treated promptly, it may become chronic and persist for years, leading to complications such as osteoarticular, hepatobiliary, cardiovascular, and central nervous system diseases (9). In addition, the disease is regarded as an important occupational hazard to livestock workers. Veterinarians, farmers, and slaughterhouse workers are vulnerable as they handle infected animals and aborted fetuses or placentae. Human brucellosis has been greatly controlled in many countries, and its epidemiological features have changed drastically over the past few decades due to the various improvements in sanitary conditions, socioeconomic development, political reasons, and the increasing domestic and international human mobility (4–6,10). However, considering the large number of cases reported across the world each year and its serious health consequences and socioeconomic impacts, human brucellosis remains a global public health challenge, especially in regions where animal infections are common. Fox example, brucellosis is considered endemic in most Middle Eastern countries with a high number of human cases reported in Yemen, Iran, Syria, Turkey, and Saudi Arabia in recent years (6,11). The highest annual incidence rate was recorded in Yemen (88.6 cases/100,000 person-years), Syria (40.6/100,000), and Iran (18.6/100,000) in 2014–2017 (6). McDermott JJ et al. (2) found a high average prevalence (11%) among high-risk human populations in Africa and Asia, such as veterinarians, livestock handlers, and slaughterhouse workers, suggesting that brucellosis is an ongoing epidemic in African and Asian continents. Data on incidence of brucellosis are often underreported because the surveillance system relies on passive reports that collect information from hospitals and diagnostic laboratories, especially in areas with low capacities of healthcare and diagnosis. Therefore, the real burden of human brucellosis in low-income countries may be far greater than figures reported. However, human brucellosis is also reported in some high-income countries where brucellosis has been eliminated or transmitted at a relative low level. For instance, 381 confirmed cases of brucellosis were reported by 28 European Union countries in 2017 with an overall rate of 0.09 cases/100,000 person-years (12). Greece, Italy, and Spain reported the highest numbers of confirmed cases, accounting for 67.2% of all cases. Greece had reported the highest incidence rate, followed by Italy and Portugal, as well as Spain and Sweden. In Sweden, all cases occurred in travelers from countries with ongoing epidemics. China CDC Weekly