Abstract
Brucellosis is a widespread zoonotic disease of public health importance that is often associated with occupational exposure. Despite brucellosis being considered a priority zoonotic disease in South Africa, the true incidence and prevalence of the disease in animals and humans is largely unknown. To enhance the current understanding of human brucellosis in South Africa, the persistence of Brucella antibodies and the number of new infections in a farming community were investigated. A longitudinal study was conducted in a farming community within a 40 000 km2 area in the Free State and Northern Cape provinces, South Africa. Participants (n=232) were selected from three cross-sectional studies conducted over a 36-month period from 2015-2018. Participants enrolled in at least the first and last surveys were included in the cohort. Seroprevalence was determined using an anti-Brucella IgG enzyme-linked immunosorbent assay (ELISA). Seropositive samples were tested further using an anti-Brucella IgM ELISA and immunocapture agglutination test to assess the antibody profiles. Statistical analysis was conducted using STATA v14. Of 232 participants, 87.9% (204/232) were from a farming population (people living and working on 102 domestic and game farms) and 12.1% (28/232) were (para)veterinary professionals. The median age was 39 years(interquartile range: 31-51 years) at first enrolment and 84.9% (197/232) were male. The IgG seropositivity was 13.4% (31/232), 14.2% (19/134) and 12.9% (30/232), respectively for the three surveys. Of the reactors, 83.9% (26/31) remained IgG seropositive and at least 6.5% (2/31) also had persistent IgM antibodies. Five of the participants seroconverted over the study period. This is the first longitudinal cohort study investigating human brucellosis in South Africa. A large proportion of reactors had persistent specific antibodies over the 36-month study period. Because unrecognize seroconversion was detected in the farming community, it is possible that more individuals were antibody-positive than would otherwise be reported, and that they could have ongoing infection if not treated appropriately. The findings from this study once again highlight the need to interpret serological results in light of the clinical context for the diagnosis of active brucellosisin high-risk populations especially in endemic areas.
