Abstract:
Bovine brucellosis is a worldwide, zoonotic infection caused by Brucella species bacteria and characterised by abortions and retained placentae in cows and, to a lesser extent, orchitis in bulls. The disease is a zoonotic risk (causing undulant fever, Mediterranean fever or Malta fever in humans) for those working with breeding cattle and threatens both food security and food safety. Accordingly, control and ultimately eradication of the disease is a goal of most countries where it occurs in order to enhance animal health and protect human health.
The aim of this study was to assess the herd level risk factors associated with occurrence of brucellosis in the Eastern Cape, South Africa, in order to assist the veterinary authorities to implement and/or enhance strategies that can control the disease at farm level. The study is part of a multiple-location study in different provinces of South Africa to investigate risk factors where case numbers are limited locally but where the power of the study is increased, when combined with the other concomitant studies.
A case control study design was used. Case herds were defined as those with culture-positive herds or more than two complement fixation test (CFT) - positive reactors, in the absence of adult Strain 19 vaccination, between 2013 and 2017. Control herds were defined as those that tested negative within six months of infection being detected in case herds and which had no history of brucellosis. A total of 77 farms were recruited for the study, comprising 30 cases and 47 controls. A pre-trialled questionnaire was used to conduct interviews on case and control farms by trained animal health officials. Assessed risk factors included herd characteristics, cattle movements, potential brucellosis contacts, presence of wildlife and management/employee knowledge. Data were transferred to a Microsoft Access 2013 database and analysed in Excel 2013 and SPSS (IBM, Version 25). A univariate analysis was undertaken to examine the association between case-control status and potential risk factors. Significant risk factors at that stage included abortions in the herd, Brucella positive neighbours, use of artificial insemination with or without a bull, the proportion of cows/heifers greater than 0.64, the farming status of the herd (i.e. being commercial) and herd type (dairy). When presented for a logistic regression analysis, the only remaining variable was abortions in the herd (OR 27; CI 5.958 – 123.795).
