Abstract
In South Africa, the prevalence of cattle handler exposure to Brucella on cattle farms is unknown and risk factors and cattle symptoms associated with infected cattle herds are unavailable. To address this gap, a case-control study of cattle herds was conducted in Gauteng province and farm workers and veterinary officials were tested for exposure to Brucella. Seroprevalence amongst farm workers exposed to case herds ranged from 4.0% (BrucellaCapt®) to 16.7% (IgG ELISA®), compared to those exposed to control herds, where seroprevalence ranged from 1.9% (BrucellaCapt®) to 5.7% (IgG ELISA®). Seroprevalence amongst veterinary officials was significantly greater compared to farm workers exposed to case herds for the outcome RBT+ IgM- IgG+ (OR = 11.1, 95% CI: 2.5–49.9, p = 0.002) and RBT- IgM- IgG+ (OR = 6.3, 95% CI: 2.3–17.3, p < 0.001). Risk factors associated with being an infected herd were: being a government-sponsored farm vs. private farm (OR 4.0; 95% CI: 1.4–11.3; p = 0.009), beef vs. dairy herd (OR 7.9; 95% CI: 1.4–44.9; p = 0.020), open vs. closed herd (OR 3.3; 95% CI: 1.1–10.4; p = 0.038) and the presence of antelope on the farm (OR 29.4; 95% CI: 4.0–218.2; p = 0.001). Abortions (OR = 5.1; 95% CI: 2.0–13.3; p < 0.001), weak calves in the herd (OR = 8.0; 95% CI: 2.6–24.4; p < 0.001), reduction in number of calves born (OR = 9.0; 95% CI: 2.1–43.6; p < 0.001), reduction in conception rate (OR = 3.9; 95% CI: 0.8–18.3; p = 0.046), hygromas in cattle (p = 0.011) and farmers reporting brucellosis-like symptoms in their farm workers or in him/herself (OR = 3.4; 95% CI: 1.3–8.7; p = 0.006) were more likely to be associated with Brucella infected herds than control herds. This evidence can be used in strategic planning to protect both human and herd health.
Highlights
Brucellosis is a neglected zoonotic bacterial disease impacting public health and global agricultural development [1,2,3,4]
Our findings suggest that the IgG Enzyme Linked Immunosorbent Assay® (ELISA)® is not well adjusted to differentiate between low levels of IgG antibody circulating in exposed farm workers and veterinary officials and potential undetected clinical cases of brucellosis in this group
We found evidence of cattle handler exposure to Brucella on cattle farms participating in the provincial veterinary services’ bovine brucellosis control programme as well as significant herd risk factors and symptoms
Summary
Brucellosis is a neglected zoonotic bacterial disease impacting public health and global agricultural development [1,2,3,4]. Having one or more of the following symptoms is characteristic of cattle infected with brucellosis: abortion, retained placenta, stillbirths, poor weight gain, orchitis, epididymitis and hygromas [10]. Abortion caused by B. abortus in cattle usually occurs in the third trimester due to necrotising placentitis [6] and exposure to these tissues is the primary source of transmission to humans or uninfected bovine, which occurs through aerosolized or direct mucosal contact [11]. Infection in cattle does not always lead to abortion, but can persist in a herd without any overt clinical symptoms, other than the birth of weak or nonviable calves and a reduction in milk yield [11,12]. In utero infection or milk and colostrum can be sources of disease transmission to the new-born calf [13]
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