Rift Valley fever (RVf) is a viral disease that causes abortions and deaths mainly in sheep, goats and cattle. If animals are not vaccinated against RVf during these extensive periods of absence of RVf outbreaks the herds/flocks are totally susceptible to the disease. The inability to accurately predict future outbreaks of RVf based on rainfall predictions, makes it impossible to prophylactically vaccinate (before the onset of the disease in order to protect against the disease) susceptible animals.
RVf has been regarded as very important in South Africa for the past two years, although the last major outbreak occurred in 1974/75.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 while taking a blood meal.
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 for two main reasons. Firstly, it usually takes two to four weeks before vaccinated animals may be protected against the disease they have been vaccinated against. 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 (SAWS) 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. Neither is the resultant lower weaning percentages and the decreased number of potential replacement animals taken into account. The effect of RVf on the future of a herd/flock is much more far reaching than may be expected.
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 contract RVf by handling blood, tissue and other body fluids of RVf- infected animals. People can take the following precautions to protect themselves against infection with RVf:
1. Sick animals must not be slaughtered and the meat of sick animals or animals that have died must not be eaten;
2. Even meat from “healthy” animals must always be properly cooked before consumption;
3. Milk must be pasteurised or boiled before use;
4. A mask and gloves must be worn when slaughtering animals or working with animal tissue or aborted foetuses;
5. Carcasses of animals that have died must not be opened up in an attempt to perform your own post-mortem examination. Such cases must rather be referred to a state veterinarian, private veterinarian or animal health technician to perform the test.
People should immediately go to their nearest clinic if they suspect that they have contracted RVf. It is also very important to inform the attending doctor that RVf is suspected as the cause of the disease.
RVf is a notifiable disease in terms of the Animal Diseases Act, 1984 (Act No. 35 of 1984). It is therefore compulsory by law to report any confirmed or suspect RVf cases to the nearest state veterinarian, private veterinarian or animal health technician.
DAFF advises livestock owners to vaccinate their animals against RVf owing to the predicted La Niña conditions that may pose a risk of an outbreak.
For further information on RVf in animals and assistance with vaccination advice, please contact your nearest state veterinarian, private veterinarian or animal health technician.
For assistance in locating the nearest state veterinary office, please contact:
The Directorate of Animal Health
Department of Agriculture, Forestry and Fisheries
Tel: 012 319 7456
For further information on RVf in humans, please contact:
The Department of Health
Cell: 012 395 8000
For further information contact:
Mr Steve Galane
Acting Chief Director: Stakeholder Relations and Communications
Department of Agriculture, Forestry and Fisheries
Cell: 083 635 7346
Tel: 012 319 7960
Fax: 012 319 6943
E-mail: DAIS@daff.gov.za or stevegalane@mtn.blackberry.com
