By Charl van Rooyen
Livestock experts are urging vigilance concerning Rift Valley fever, as it may resurge in Southern Africa at any moment due to heavy rainfall in certain regions and extensive mosquito breeding.
This disease among livestock also poses a significant threat to humans and can result in death. Hunters’ practice of smearing newcomers’ faces with blood and asking them to eat raw liver as a form of initiation is now being questioned, as game infected with the disease can transmit it to these individuals. During the previous major outbreak of Rift Valley fever in 2010, losses incurred by farmers amounted to approximately R2.253 billion, not to mention the extensive indirect damage due to genetic and reproductive losses.
Dr Faffa Malan, a consulting livestock health expert from Pretoria, advises farmers to remain vigilant. Due to high rainfall in many regions, conditions are favourable for a new outbreak. The Anopheles mosquito species, which transmits this viral disease to sheep, goats, cattle, and game, is now breeding in water pools. Furthermore, the Culex and Aedes species can also transmit the virus.
Malan says many farmers no longer vaccinate their animals, heightening their risk during Rift Valley fever outbreaks. Onderstepoort Biological Products (OBP) is the only vaccine manufacturer in South Africa. During an outbreak, there is an increase in farmers wishing to purchase the vaccine, potentially leading to shortages. Farmers should assess their risk. If you are farming in a high-risk area, you must vaccinate your animals before the rainy season, as it will be too late to act if the disease emerges on your farm.”
Design Biologix, a private vaccine manufacturer based in Pretoria, developed a vaccine for Rift Valley fever some time ago and has applied for registration with the registrar under the Fertilisers, Farm Feeds, Agricultural Remedies, and Stock Remedies Act (Act No. 36 of 1947). Dr Angela Buys, the CEO of Design Biologix, informed African Farming that they are still awaiting registration. Once they receive approval, they can commence full-scale manufacturing of this vaccine.
Internal organs turn golden yellow
Individuals can become infected if they cut open a dead animal. “The internal organs of an infected animal turn golden yellow. Do not touch them, as this may lead to infection and even death,” warns Malan. He cautions against the practice among hunters of smearing the faces of novice hunters – including children – with buck blood after they have shot their first buck, as well as consuming a piece of raw liver. “If that buck has Rift Valley fever, hunters can contract the disease.” Any suspicion of the disease in an area should be reported immediately to a local or state veterinarian.
The best practice is to vaccinate animals preventively before the rainy season begins. Live vaccines can be used for this purpose, but they should not be administered to pregnant animals, as this may lead to abortions. For pregnant animals, an inactivated vaccine is recommended. Malan has firsthand experience of the disruptions caused by Rift Valley fever. Decades ago, he worked as a veterinarian in Vrede in the Eastern Free State during a significant outbreak of Rift Valley fever, which resulted in a considerable number of abortions in sheep. Farmers faced substantial financial losses.
Human risk
Prof. Leon Prozesky, owner of Path Diagnostics and former professor of pathology at the University of Pretoria’s Faculty of Veterinary Science, fell ill in 1975 after performing a post-mortem examination on a sheep. During the 1990s, veterinary students also became unwell after dissecting an animal’s carcass. One student contracted a severe form of Rift Valley fever, specifically meningitis, but miraculously recovered. He notes that the risk of infection for humans is particularly heightened during large-scale outbreaks of Rift Valley fever, as they may become infected by handling contaminated animals, exposure to bodily fluids, or even mosquito bites.
Symptoms can vary from moderate flu-like indications such as fever, headache, and muscle pain to severe manifestations like haemorrhagic fever, encephalitis (brain inflammation), and eye complications. Pregnant women are particularly at risk due to the potential for miscarriage.
Prozesky states when an “abortion storm” occurs on a farm and individuals exhibit flu-like symptoms, these are often the primary indicators that it may be Rift Valley fever. South Africa experiences periodic outbreaks among livestock, particularly in regions where extensive farming practices are common. In addition to causing fatalities among livestock, Rift Valley fever also results in widespread abortions in animals. “There have been instances where up to 90% of the sheep on a farm have aborted. It is crucial for veterinarians and farmers to remain vigilant for the disease and to adopt management strategies such as the early vaccination of animals. From the authorities’ perspective, efforts are ongoing to raise public awareness that they, too, can contract Rift Valley fever. Fortunately, the disease is not transmissible from person to person.” People should avoid touching infected animals and employ repellents during outbreaks to deter mosquitoes.
“Buffalo can transmit Rift Valley fever,” says Johann Kotze, manager of the MSD test farm at Malalane, which experienced an outbreak in 2008. It began with sudden deaths among buffalo calves in the nearby Kruger Park. One of his staff members also fell ill but fortunately recovered. People can go blind from Rift Valley fever. Research he has reviewed indicates that wildlife does not necessarily exhibit symptoms. This may be because wildlife is not managed as closely as livestock. He warns against the practice of smearing new hunters with blood and making them eat liver. “It is dangerous, not only because of Rift Valley fever but also because they can contract other diseases.”
Risk always present
There is always a possibility that Rift Valley fever could break out. However, it is not necessarily a significant risk at the moment, says Prof. Peter Thompson, professor of veterinary epidemiology in the Department of Production Animal Studies at the University of Pretoria. He advises farmers to vaccinate promptly. Farmers in the northern regions face a higher risk than those in the drier parts of the Free State.
During the calving season, there is also a risk of losing cattle if the disease occurs, which can lead to substantial financial losses. Malan notes that animals currently have low immunity against Rift Valley fever, as the last outbreak was quite some time ago. Although the disease did occur in Jacobsdal, it was an isolated incident. He says farmers must remain on high alert and report suspicious cases immediately.
