ISDS Annual Conference Proceedings 2019. This is an Open Access article distributed under the terms of the Creative Commons 

AttributionNoncommercial 3.0 Unported License (http://creativecommons.org/licenses/by-nc/3.0/), permitting all non-commercial use, 

distribution, and reproduction in any medium, provided the original work is properly cited. 

Online Journal of Public Health Informatics * ISSN 1947-2579 * http://ojphi.org * 11(1): e408, 2019 

ISDS 2019 Conference Abstracts 

Seroprevalence and factors associated with seropositivity 
to Rift Valley fever virus in livestock 

Yusuf B. Ngoshe1, Lida Avenant1, MK Rostal2, Karesh B. William2, Janus T. Paweska3, Jansen 
van Vuren3, Claudia Cordel4, Veerle Msimang3, 1, Peter N. Thompson1 

1
Epidemiology Section, Production Animal StudiesStudy, University of Pretoria, Pretoria, Gauteng, South Africa, 

2
EcoHealth Alliance, NYC, New 

York, United States, 
3

National Institute for Communicable Diseases, Pretoria, Gauteng, South Africa, 
4

Execuvet, Bloemfontein, Free State, 
South Africa 

Objective 

The objective of this study was to estimate the prevalence of antibodies to RVFV in domestic cattle, sheep, and goats in a 

study area in the central interior of South Africa, and to identify factors associated with seropositivity. 

Introduction 

Rift Valley fever (RVF) is a mosquito-borne viral zoonosis. This study aimed to estimate the prevalence of antibodies to RVF 

virus (RVFV) in cattle, sheep, and goats in South Africa, near the 2010-2011 outbreak epicenter and identify factors associated 

with seropositivity. 

Methods 

A cross-sectional study was conducted during 2015-2016 within a ~40,000 km2 region between Bloemfontein and Kimberley. 

Farms were selected using random geographic points with probability proportional to the density of livestock-owning 

households. Livestock were randomly sampled from the farm closest to each selected point. A questionnaire was used to collect 

information concerning animal, management, and environmental factors. Sera samples were screened for RVFV antibodies 

using IgG inhibition ELISA. Data were analyzed using multilevel logistic regression  models. 

Results 

On 234 farms, 3,049 animals (977 cattle, 1,549 sheep and 523 goats) were sampled. Estimated RVF seroprevalence, adjusted 

for clustering and sampling weights, was 42.9% (95% CI: 35.7-50.4%) in cattle, 28.0% (95% CI: 21.3-35.4%) in sheep and 

9.3% (95% CI: 5.8-13.9%) in goats. Compared to animals <2y of age, seroprevalence was higher in animals 2-4y (OR=2.8, 

P<0.001) and >4y old (OR=17.0, P<0.001). Seroprevalence was also higher on private vs. communal land (OR=4.3, P=0.001) 

and was positively associated with the presence of perennial rivers (OR=1.6, P=0.03) and seasonal pans (OR=1.8, P=0.005) 

on the farm. The odds of seropositivity was higher in domestic ruminants recently vaccinated between 2014-2015 (OR=2.1, 

P=0.007) compared to those never vaccinated. 

Conclusions 

The presence of IgG antibody against RVFV among domestic ruminants, born after the most recent outbreak (<4y category), 

and association with known RVF risk factors, indicates the possibility that viral circulation has occurred during the inter-

epidemic period. 

Acknowledgement 

The authors acknowledge and are extremely grateful to all the farmers that participated in this study and to the state 

veterinarians and animal health technicians of Free state and Northern Cape Provinces for facilitating identification of farms 

and contacts with the farmers. We also thank Karissa Whiting for the development of the electronic mobile application for 

the survey data collection. The field and laboratory work for this project was funded by the Understanding Rift Valley Fever 

in South Africa Project, sponsored by the U.S. Department of Defense, Defense Threat Reduction Agency. The content of 

the information does not necessarily reflect the position or the policy of the federal government, and no official endorsement 

should be inferred. The EcoHealth Alliance, University of Pretoria and National Research Foundation are acknowledged for 

financial support. 

http://ojphi.org/