Comprehensive study on human brucellosis seroprevalence and Brucella species distribution in Iran (1970-2023)

Brucellosis is a zoonotic bacterial disease that causes enormous economic losses in livestock populations and severe debilitation in humans globally. This study analyzes the seroprevalence of human brucellosis in Iran from 1970 to 2023, revealing key epidemiological trends based on data from 20,046 individuals. Through serological, culture, and molecular tests, it identifies the Brucella species affecting humans over five decades. The findings emphasize the need for ongoing monitoring and improved disease control efforts. Subsequently, we cultured specimens from seropositive individuals who exhibited suspected symptoms of brucellosis. The specimens included blood (n = 9017), placentas (n = 203), bone marrow (n = 221), aborted fetuses (n = 70), cerebrospinal fluid (CSF) (n = 62), synovial fluid (n = 5), urine (n = 4), sperm (n = 3), lumbar discs (n = 3), abscesses (n = 2), milk (n = 2), and vertebral bodies (n = 1). The overall seroprevalence of brucellosis in Iran was 44.9 % based on RBPT, 20.7 % by SAT, and 8.7 % by 2-ME tests. The highest SAT prevalence occurred in the 2000s (25.8 %), followed by the 1990s (23.8 %), 1980s (22.2 %), 1970s (14.8 %), and 2010s (10.4 %). Two main Brucella species were identified in infected humans as Brucella melitensis and Brucella abortus. Positive culture rates varied by sample type, with 9.9 % for blood, 10.4 % for bone marrow, and up to 100 % for fluids like urine and milk. The most common strain was B. melitensis biovar 1 (89.2 %), while B. abortus biovar 1 had a much lower incidence (0.3 %). This investigation showed that the highest rates of culture positivity were in samples of urine, synovial fluid, abscess, and milk. These findings suggest that B. melitensis continues to be an important public health concern and that recent years of decline may be due to better control measures of the disease. The combined use of serology and culture is recommended for diagnosing brucellosis. Increased awareness among farmers and consumers of raw dairy products, coupled with nationwide control measures, is crucial for combating zoonotic brucellosis.