A team of international researchers have for the first time discovered the first estimates for risk factors of Rift Valley fever (RVF) incidence in livestock.

Rift Valley fever (RVF) is a severe viral disease that can cause infections of the brain and bleeding. It is spread by either touching infected animal blood, breathing in the air around an infected animal being butchered, drinking raw milk from an infected animal, or the bite of infected mosquitoes.

The major hosts of the mosquitos carrying the virus are sheep, cattle and goats, although the disease can affect other mammals including humans.

The disease is mainly present in Africa, representing a threat to human health, animal health and production.

The aim of the present study, published in Nature Scientific Reports, was to investigate environmental factors involved in the observed spatial pattern of RVF cases in South Africa, across five outbreak waves between 2008 and 2011.

Dr Lisa Collins from the School of Life Sciences, University of Lincoln, UK, jointly supervised lead author Dr Raphaelle Metras, who is now based at the London School of Hygiene and Tropical Medicine.

The researchers discovered that up until 2010 an increase in vegetation density was the most important risk factor. In 2010, increased temperature was the major risk factor. In 2011, after the large 2010 epidemic wave, these associations were reversed, potentially confounded by immunity in animals, probably resulting from earlier infection and vaccination.

The research concluded vegetation density and temperature should be considered together in the development of risk management strategies. However, the crucial need for improved access to data on population at risk, animal movements and vaccine use is highlighted to improve model predictions.

Due to data scarcity, no previous study had quantified risk factors associated with RVF epidemics in animals in South Africa.