The inability to accurately predict future outbreaks of RVf based on rainfall predictions makes it impossible to prophylactically vaccinate susceptible animals.
Major RVf outbreaks occur at irregular intervals of 5 to 15 years, or even longer, and have always been associated with abnormal high rainfall, which may result in an increased number of mosquitoes. RVf-infected mosquitoes transmit the virus to animals.
Animals should be vaccinated before the onset of an outbreak of the disease. Vaccinating only in the threat of an outbreak may not be effective because it usually takes two to four weeks before vaccinated animals may be protected against the disease. Secondly, the virus may be spread from one animal to another if the same needle is used to vaccinate different animals.
Veterinary epidemiologists at the Department of Agriculture, Forestry and Fisheries (DAFF), have analysed previous outbreaks of RVf in South Africa and have found that high rainfall from December to February can trigger severe RVf outbreaks. The South African Weather Service has sent out a warning of possible La Niña conditions over South Africa from December 2011 to February 2012, which may result in above-normal rainfall.
During the 2010 RVf outbreak, 8 800 animals were reported to have died, and a further 3 600 animals were reported to have died from 1 January 2011 to 31 August 2011. These figures do not take into account the number of abortions that have gone unnoticed in extensive farming practices.
RVf can also cause disease in humans, usually resulting in flu-like symptoms two to six days after contact with the virus. However, RVf could cause more severe symptoms and even death. During 2010 there were 238 confirmed human RVf cases and 26 confirmed human deaths because of RVf. From 1 January 2011 to 24 June 2011 there were a further 37 confirmed human RVf cases but no further human deaths were confirmed as a result of the disease.
People can contract RVf by handling blood, tissue and other body fluids of RVf- infected animals and should immediately go to their nearest clinic if they suspect that they have contracted RVf.
