Seroprevalence and risk factors of brucellosis in pastoralists and their livestock in Central Equatoria State, South Sudan
Authors: Lita Emmanuel P. , Ochi Erneo B. , Misinzo Gerald , van Heerden Henriette , Katani Robab , Godfroid Jacques , Mathew Coletha 
Published: December 2024

Background
Brucellosis poses serious public health implications and substantial economic losses in pastoral rural settings in South Sudan. In humans, brucellosis is almost always originating from animals. Current literature provides scant data regarding the seroprevalence of brucellosis in South Sudan. This cross-sectional study investigates the seroprevalence of brucellosis among the pastoral community and livestock and identifies risk factors for the disease from two Counties, Terekeka and Juba in Central Equatoria State (CES), South Sudan.

Methodology
A total of 986 sera; from humans (n = 143), cattle (n = 478), sheep (n = 86), and goats (n = 279) were randomly collected from 17 cattle camps in CES. Sera for the humans, cattle and goats were screened for Brucella-specific antibodies using Rose Bengal plate test (RBPT) and further confirmed by competitive enzyme-linked immunosorbent assay (c-ELISA) in series due to the cost of testing. All the sera from sheep were tested in parallel using RBPT and c-ELISA as the sheep samples were few and were all tested negative on the RBPT. A camp was considered positive when at least one animal of either species tested positive on the c-ELISA. A structured questionnaire was used to collect information on potential individual and herd level risk factors. Univariate analysis using binary logistic regression with a confidence interval of 95% at a p-value of ≤ 0.05 was used to identify the association between the potential individual risk factors and Brucella seropositivity. The investigated risk factors for livestock included age, sex, species, prior abortion history, retained placenta, parity, and reproductive status. Variables found to have associations in univariate analysis (p = 0.25) with Brucella seropositivity were further included in multivariable logistic regression. The risk factors investigated for humans included, gender, age, educational level, occupation, marital status, drinking of raw milk, aiding female animals during delivery, eating undercooked meat and blowing of air into the cow’s uterus through the vagina, a practice in South Sudan.

Results
The study revealed seroprevalence of 21.7%, 11.8%, and 4.8% in cattle, goats, and humans, respectively. Our results indicated that all sheep serum samples were negative on both RBPT and c-ELISA. The seropositive in the 13 camps from Terekeka County was 100.0% (13/13) compared to 50.0% (2/4) seropositive from 4 camps in Juba County. All the variables investigated in the univariate analysis of risk factors in cattle were significantly associated with Brucella seropositivity: sex (OR:4.5, 95% CI: 2.2–8.9, p<0.001), age (OR:6.6, 95% CI: 2.3–19.1, p:<0.001), abortion history (OR:3.1, 95% CI: 1.8–5.2, p:<0.001), retained placenta (OR:2.5, 95% CI: 1.4–4.4, p = 0.001), parity (OR:2.3, 95% CI: 1.1–4.7, p = 0.020), However, in small ruminants, none of the potential risk factors were associated with Brucella seropositivity. In humans, blowing air through a cow’s vagina (OR: 1.4, 95%CI: 0.782–2.434, p = 0.035) was the only variable found to be significantly associated with Brucella seropositivity in the univariate analysis. The forceful blowing of air into a cow’s vagina to induce milk letdown is a common practice among the pastoral communities in South Sudan.
The multivariable logistic regression model identified sex, age, and abortion history as statistically significant factors for Brucella seropositivity in cattle. The odds of seropositivity were nearly threefold (OR: 2.8; 95% CI: 1.3–5.8, p = 0.006) higher in cows compared to bulls (male cattle). Cattle over two years old had higher odds of Brucella seropositivity than young animals (OR: 3.5, 95% CI: 1.2–10.3-, p: 0.025). Cows with a history of abortion had higher odds of Brucella seropositivity (OR: 2.8, 95% CI: 1.6–4.7, p = 0.001).

Conclusion
This study reports the occurrence of brucellosis in goats and its absence in sheep in (CES), South Sudan. The present study also shows the occurrence of brucellosis in cattle, goats and people in the pastoral community and recommends for the implementation of the One Health approach and awareness campaigns for effective mitigation of this disease.