Farm-Level Risk Factors of Increased Abortion and Mortality in Domestic Ruminants during the 2010 Rift Valley Fever Outbreak in Central South Africa.

Melinda K Rostal,William B Karesh,Daniel T Haydon,Louise Matthews,Janusz T Paweska,Sarah Cleaveland,Noam Ross,Lara Van Staden,Assaf Anyamba,Claudia Cordel

doi:10.3390/pathogens9110914

Abstract

(1) Background: Rift Valley fever (RVF) outbreaks in domestic ruminants have severe socio-economic impacts. Climate-based continental predictions providing early warnings to regions at risk for RVF outbreaks are not of a high enough resolution for ruminant owners to assess their individual risk. (2) Methods: We analyzed risk factors for RVF occurrence and severity at the farm level using the number of domestic ruminant deaths and abortions reported by farmers in central South Africa during the 2010 RVF outbreaks using a Bayesian multinomial hurdle framework. (3) Results: We found strong support that the proportion of days with precipitation, the number of water sources, and the proportion of goats in the herd were positively associated with increased severity of RVF (the numbers of deaths and abortions). We did not find an association between any risk factors and whether RVF was reported on farms. (4) Conclusions: At the farm level we identified risk factors of RVF severity; however, there was little support for risk factors of RVF occurrence. The identification of farm-level risk factors for Rift Valley fever virus (RVFV) occurrence would support and potentially improve current prediction methods and would provide animal owners with critical information needed in order to assess their herd’s risk of RVFV infection.

Highlights

Rift Valley fever virus (RVFV) is a zoonotic arbovirus that can cause widespread outbreaks interspersed with periods of very few clinical cases
2010 RVF regional outbreaks in South Africa was lower than is typically reported for RVF outbreaks in the literature
We specified a Bayesian multinomial hurdle model to identify risk factors of the number of deaths and abortions that occurred during an RVF outbreak

Summary

Introduction

Rift Valley fever virus (RVFV) is a zoonotic arbovirus that can cause widespread outbreaks interspersed with periods of very few clinical cases. The ecology of RVFV results in an ongoing cycle of endemic and epidemic periods, understanding this allows the identification of several potential risk factors for RVF outbreaks. The epidemic cycle of RVF, causing large and widespread outbreaks, is thought to be driven by environmental conditions. This includes flooding caused by abnormally high and prolonged precipitation events [14,15] that support massive breeding of mosquitos that are competent horizontal vectors of RVFV (e.g., Culex spp.), which amplifies RVFV infection in susceptible animals

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