"Reported cases so late in the season – it is already winter in the southern hemisphere – is worrying. It’s not because we can expect a full-blown epidemic right away, but cases now point to a very good chance of a serious outbreak in summer."
Rift Valley Fever is caused by a virus that is transmitted by mosquitoes. They might be inactive in cold weather, but mosquitos have already feasted on the blood of infected animals. This means that come summer, swarms will emerge as active carriers. "If farmers do not take decisive preventative action now in winter, December could be a Rift Valley Fever bloodbath," says Oberem.
Dramatic as it may sound, Oberem is not exaggerating. Rift Valley Fever is a devastating disease in small livestock, especially sheep. Up to 90% of lambs die within days of being infected, and between 40% and 100% of pregnant ewes that are infected will abort. While it also occurs in cattle, buffalo and antelope, the disease is neither as virulent nor as fatal in those species as in sheep. Rift Valley Fever is furthermore a zoonotic disease, meaning it can spread from animals to people. As such, it is a One Health concern.
While humans cannot be infected by mosquitoes, they are very likely to get ill if they come into contact with the blood of sick or dead animal and/or aborted foetuses.
Veterinarians are, therefore, particularly at risk. During the last significant outbreak in South Africa, a young veterinarian from the Eastern Cape died of the disease. Although not always fatal in humans, the virus attacks the liver and recovery is slow and difficult. "The biggest mistake farmers can make is to be complacent in winter," says Oberem.
Although sheep are more at risk, cattle should also be vaccinated to prevent mosquitoes feeding on them from ingesting and then transmitting the virus. Oberem explains there are two types of Rift Valley Fever vaccine, namely live and inactivated (or killed). The latter has to be used in animals that are or could be pregnant. Giving them the live vaccine would cause abortions or the birth of deformed lambs. The inactivated vaccine has to be given twice, unlike the live vaccine for which only one application is necessary.
Farmers should be careful when handling the live vaccine so as to not accidentally infect themselves. Rift Valley Fever vaccines are currently only manufactured at Onderstepoort. However, farmers will have another option in the near future when the vaccine developed by Afrivet is registered.
"We have to control the disease while we have the opportunity to do so. I am pleased that the state veterinary services have assured me that they are taking the matter seriously and are agreeing that farmers have to be warned to vaccinate now. If not, we will pay the price in livestock deaths and maybe even human casualties, says Oberem.
An outbreak is also likely to hurt the export industry. Countries in the Middle-East have already banned South African lamb imports following the previous outbreak. "Rift Valley Fever is a One Health concern because human activity in the environment aggravates it. We have to take responsibility by controlling the water bodies where mosquitoes breed and by vaccinating our livestock," concludes Oberem.
