Determinants of bovine brucellosis across herds and individuals: A Bayesian meta-analysis

Abstract

Bovine brucellosis, which is caused primarily by Brucella abortus, is a widespread zoonotic disease that threatens cattle health and productivity and poses public health risks, leading to major economic losses. Although numerous risk factors-from husbandry practices to animal health conditions-have been implicated, findings across individual studies remain inconsistent, leaving a critical knowledge gap concerning the primary drivers of infection. We systematically searched PubMed, Web of Science and ScienceDirect databases and ultimately identified 58 observational studies published between 2000 and 2024 for a stratified Bayesian meta-analysis to quantify the strength of the associations between candidate risk factors and brucellosis infection. Excluding the overlap between the population level and the individual animal level, a total of 14 risk factors that may be associated with bovine brucellosis infection were identified. Cohousing with small ruminants poses significant risks at both the herd (OR=1.76, 95 % CI: 1.23-2.46) and individual levels (OR=2.76, 95 % CI: 2.20-3.45). Vaccination shows protective associations at the individual level (OR=0.67, 95 % CI: 0.54-0.84) but is associated with higher measured herd-level seropositivity under non-DIVA testing (OR=1.54, 95 % CI: 1.02-2.23). Multiparity (OR=2.41, 95 % CI: 1.60-3.50) and sex (male) (OR=0.67, 95 % CI: 0.56-0.81) were significant factors at the individual level. At the herd level, purchasing animals from outside (OR=1.88, 95 % CI: 1.33-2.57), farmer knowledge of brucellosis (OR=0.38, 95 % CI: 0.24-0.55) and on‑site veterinary oversight (OR=0.46, 95 % CI: 0.17-0.96) were significant factors. Communal grazing, wildlife contact, visitor restrictions, artificial insemination, dedicated facilities, disinfection, and borrowing of bulls were not significant. At the animal level, artificial insemination and the ability to purchase animals from the outside also showed no significant associations. This study identified seven risk factors related to brucellosis: co‑housing with small ruminants, vaccination, multiparity, sex (male), purchasing animals from outside, farmer knowledge of brucellosis and on‑site veterinary oversight. Among them, cohousing with small ruminants and multiparity are individual-level risk factors for animals, whereas vaccination and sex (male) are protective factors. Cohousing with small ruminants, purchasing animals from outside and vaccination are risk factors at the group level, and farmer knowledge of brucellosis and onsite veterinary oversight are protective factors. Livestock farmers should be encouraged to raise cattle and small ruminants separately, learn about the prevention and control of bovine brucellosis, and veterinarians should be stationed on the farm.

Keywords: Bayesian meta-analysis; Biosecurity; Bovine brucellosis; Risk factors.