Seroprevalence, associated risk factors, and molecular detection of Brucella spp. in cattle, sheep, goats and humans in Mvomero district, Morogoro, Tanzania.

Abstract

Background: Brucellosis is a zoonotic disease of public health and economic importance worldwide. A cross-sectional study using simple random and purposive sampling techniques was conducted from May 2024 to October 2024 in agro-pastoral areas of Mvomero district, Morogoro Region. The aim of this study was to determine the seroprevalence of brucellosis, associated risk factors, and characterize the circulating Brucella spp., in livestock and humans.

Methods: A total of 918 serum samples were collected from Mvomero district, comprising cattle (n = 339), sheep (n = 164), goats (n = 303), and humans (n = 112). Animal samples were obtained from 18 herds with mixed livestock species, while human samples were collected from four health facilities. All samples were screened for Brucella-specific antibodies using the Rose Bengal plate test (RBPT), and positive samples were subjected to competitive enzyme-linked immunosorbent assay (c-ELISA). Genomic DNA was extracted from the heparin-coated blood samples corresponding to the same samples that tested positive by c-ELISA for confirmation by using real-time polymerase chain reaction (qPCR). A herd was considered Brucella seropositive if at least one animal tested positive on c-ELISA. A structured questionnaire was used to collect information on potential individual and herd-level risk factors. A multivariate logistic regression analysis was carried out using a backward elimination procedure to identify potential risk factors, following a univariate analysis, using a p-value cut-off of 0.25 from the univariable analysis to select candidate variables for a multivariable model.

Results: At the individual level, screening by RBPT revealed seropositivity rates of 9.1% (31/339) in cattle, 4.3% (7/164) in sheep, 5.6% (17/303) in goats, and 10.7% (12/112) in humans. Subsequent results by c-ELISA demonstrated lower seroprevalence rates of 6.5% (22/339) in cattle, 1.2% (2/164) in sheep, and 2.0% (6/303) in goats. Human seroprevalence by c-ELISA was 4.5% (5/112), with all positive cases originating from a single health facility. At the herd level, the overall seroprevalence was 55.5% (10/18) based on c-ELISA results. Out of the 35 c-ELISA positive samples, 21/35 (60.0%) tested positive for the Brucella genus detection using the IS711 gene. The Brucella species-specific assay detected 17/35 (48.6%) samples as B. abortus. There was no B. melitensis detected in this study. Risk factor analysis in sheep, goats, and humans yielded no significant associations in the univariable analyses. However, multivariable logistic regression analysis in cattle identified two significant risk factors: prior history of abortion (p < 0.001, OR = 12.7, 95% CI: 3.88-41.8) and retained placenta (p = 0.023, OR = 32.5, 95% CI: 1.602-660.8).

Conclusions: Brucella abortus was the predominant circulating species in cattle, goats and humans. The significant association between brucellosis seropositivity and reproductive complications in cattle (abortion and retained placenta) underscores its economic impact on livestock productivity. We recommend serological screening of livestock and vaccination programmes in cattle and strengthened collaboration between veterinary and public health sectors through a One Health approach.