Cross-sectional study of brucellosis in Jordan: Prevalence, risk factors and spatial distribution in small ruminants and cattle

Abstract

Brucellosis is considered endemic in many Middle Eastern countries including Jordan. To determine the frequency, risk factors and spatial distribution of ruminant brucellosis in Jordan, a nationwide cross-sectional study was conducted. Small ruminant flocks (n=333) and cattle herds (n=204) were randomly selected, and their disease status was ascertained by testing individual serum samples using the Rose Bengal Test and a competitive ELISA (sheep and goats) and milk samples using an indirect ELISA (cattle). Information on putative risk factors was collected using standardized questionnaires. A logistic model with a binomial outcome was built to identify risk factors for being seropositive. The estimated true seroprevalence values were 18.1% (95% CI: 11–25.3) (cattle-only herds), 22.2% (95% CI: 16.5–28.8) (sheep flocks), 45.4% (95% CI: 30.3–61.6) (goat herds), 70.4% (95% CI: 55.5–84.9) (mixed sheep-goat flocks), 34.3% (95% CI: 28.4, 40.4) (all small ruminant flocks) and 38.5% (95% CI: 24.3–51.8) (mixed herds of cattle and small ruminants). Only 1.5% of small ruminant flocks were vaccinated. The seroprevalence was higher in northern areas, where livestock density is also higher. The logistic model fitted the data well and had a very high predictive ability. In the small ruminant model, five variables were significantly associated with a higher odds of seropositivity: lending/borrowing rams (OR=8.9, 95% CI: 3.0–26.1), feeding aborted material to dogs (OR=8.0, 95% CI: 3.5–18.1) the presence of goats (OR=6.9, 95% CI: 3.1–15.4), introducing new animals to the flock (OR=5.8, 95% CI: 2.5–13.6), and a large flock size (OR=2.2, 95% CI: 1.0–4.6). Conversely, separating newly introduced animals (OR=0.16, 95% CI: 0.05–0.47), separating animals that had aborted (OR=0.19, 95% CI: 0.08–0.46) and using disinfectants to clean pens (OR=0.37, 95% CI: 0.16–0.83) were significantly associated with a lower odds of being seropositive. The main risk factor for cattle herds being seropositive was the introduction of new animals (OR=11.7, 95% CI: 2.8–49.4); while separation of newly introduced animals (OR=0.09, 95% CI: 0.03–0.29), herd disinfection (OR=0.04, 95% CI: 0.01–0.15) and having calving pens (OR=0.14, 95% CI: 0.05–0.43) significantly reduced the odds of infection. Brucellosis is endemic at high levels across Jordan, and the current vaccination programme, which is limited to small ruminants, has very low coverage. A revised brucellosis control programme is required in Jordan. Given the high baseline prevalence, it should be based on vaccination accompanied by measures to promote hygiene and husbandry practices that minimize the risk of introduction and maintenance of Brucella spp., and thereby the risk of human infection.