Epidemiology

Brucellosis is one of the most common zoonotic diseases worldwide.[5]

Different species of Brucella tend to affect certain animal hosts and are more common in specific geographic locations:

  • B melitensis

    • Worldwide, but especially southern Europe and the Mediterranean, Middle East, Asia, and Latin America

  • B abortus

    • Worldwide

  • B suis

    • Worldwide, but especially the US, southeast Asia, and South America

    • Present in feral pigs in Australia[6]

  • B canis

    • Worldwide

  • B neotomae

    • Case reports of human cases

  • B ovis

    • No human cases

  • B pinnipediae

    • Case report of human case

  • B cetaceae

    • Case report of human case

  • B inopinata BO1

    • Case reports of human cases.

The global annual incidence of human brucellosis is not truly known, owing to variation and inadequate surveillance systems between countries, but is thought to exceed 10 in 100,000 in certain populations.[5] Major endemic areas worldwide include the Mediterranean, the Arabian Gulf, Central Asia, and parts of Central and South America.[2][7][8]​​ There is evidence that the infection is common but under-reported in India, and emerging in other parts of the world (e.g., Polynesia, Thailand, and Vietnam).[9][10][11][12][13][14] In resource-poor settings, disease is more common among the rural poor, who engage in animal husbandry and have less access to health care.[15][16][17][18] In these settings, there is also household clustering of infection.[9][12][19][20] In Europe, the incidence of brucellosis is inversely related to the gross national product of the country, and in countries where animal infections have been eradicated, human cases are usually related to travel or immigration.[5][21][22] An average of 30 cases per year are diagnosed in Australia (1.6 cases in 1,000,000 population), with 18 cases reported in 2021.[6][23]​​​​

Worldwide, B melitensis is the most common species to infect humans, although some studies have suggested that up to 73% of cases of brucellosis in certain areas of the US may be due to B abortus.[5] The majority of cases reported in the US between 1979 and 2002 were in California and Texas, particularly among the Latino population and those traveling to and from Mexico. There were 18 cases reported in the US in 2022.[24]​ In September 2017, people who consumed raw milk or milk products from a Texas dairy were traced and given postexposure prophylaxis against the RB51 strain (the B abortus strain used in animal vaccines) after a woman was diagnosed with brucellosis and other cases were suspected.[25][26] In November 2017, a warning was issued for people who drank raw milk in Connecticut, New Jersey, New York, and Rhode Island.[27] In November 2018, another warning was issued for people who drank raw milk from a farm in Quarryville, Pennsylvania (also due to the RB51 strain).[28]

Brucellosis tends to be an occupational disease predominantly affecting farmers, animal handlers, abattoir workers, veterinarians, and feral pig hunters. Among livestock-related occupational groups, the global pooled prevalence was 14% between 2000 and 2021.[29] It may also occur in laboratory personnel working with cultures. Between 1979 and 1999, approximately 8% of laboratory-acquired infections in the US were due to Brucella species.[30][31]​​​ Brucellosis continues to be a hazard in the laboratory in both endemic and nonendemic countries.[32][33][34][35][36][37][38]

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