Seroprevalence and factors associated with Q fever and Rift Valley fever in goats in Moretele municipality, South Africa

Abstract

Q fever is a zoonotic disease caused by Coxiella burnetii which infects humans and a wide range of hosts including birds, mammals, ticks, fish and reptiles. Rift Valley fever (RVF) virus (RVFV) is a mosquito-borne pathogen of livestock, wildlife and humans and is found throughout much of sub-Saharan Africa, occasionally causing large scale abortions and mortality. There is little detailed knowledge of the distribution and level of occurrence of these two pathogens in South Africa. The aim of this study was to estimate the prevalence of antibodies against C. burnetii and RVFV in goats in Moretele municipality, and to identify factors associated with seropositivity to the two zoonotic pathogens. Multi-stage random sampling was conducted and sera were collected from 216 goats in 32 goat herds. A questionnaire was completed for each participating goat owner to collect information on potential animal, management and environmental risk factors, as well as potential animal health consequences of the two infections. Rift Valley fever virus antibody testing was done by ID Screen® Rift Valley Fever Competition ELISA test kit (IDVet, Grabels, France) and C. burnetii antibody testing was done by LSIVETTM Ruminant Q Fever - Serum/Milk ELISA test kit (Life Technologies, Carlsbad, California, USA) with confirmation using a virus neutralisation test (VNT). 32/216 goats tested positive for C. burnetii antibodies and the overall seroprevalence, adjusted for clustering and sampling weights was 16% (95% CI: 10.6-23.5%). The intraclass correlation co-efficient (ICC) was 0.06, indicating low to moderate clustering within herds. Multiple logistic regression revealed age as the only factor that was significantly associated with seropositivity to C. burnetii, with a higher seroprevalence in animals ≥2 years of age (26%) than in animals ≤6 months of age (6%) (odds ratio (OR) = 6.6; 95% CI: 1.6-26.7; P = 0.010). Regarding potential consequences of infection, females with a history of abortion were more likely to be seropositive (OR = 4.6; 95% CI: 1.1-20.2; P = 0.043). Goats in herds that reported >2 abortions in the 12 months prior to sampling tended to have a higher odds of seropositivity than animals in herds with no reported abortions (OR = 2.5; 95% CI: 0.9-6.8; P = 0.071). 1/216 goats tested ELISA-positive for RVF virus antibodies and 3 samples were “doubtful”; however, they all tested VNT-negative. The estimated seroprevalence of RVFV was therefore 0% (95% CI: 0.0-1.4%). In this study, the herd seroprevalence of C. burnetii was high at 51% and there was possibility that C. burnetii is a likely cause of abortions in goats in Moretele municipality of South Africa. Seropositivity to RVFV could not be demonstrated in this study; but if present, the virus is likely to be circulating at very low levels.