An urgent call for farmers nationwide to vaccinate their cattle, sheep, pigs and goats against an acute viral disease has been issued by both government and Afrivet, an animal health products provider.
Rift Valley Fever (RVF) is spread to livestock through the bite of infected mosquitoes, but can also infect humans. Farmers therefore need to act swiftly, says Afrivet, cautioning that an outbreak is expected as early as February this year.
Impact of rainy conditions
Afrivet chief executive Dr Peter Oberem explains that humans are mainly infected through the handling of sick or dead animals.
However, based on international research, it seems that RVF infections in humans are more likely to come from mosquitoes than cattle. When humans are infected, they can experience a mild flu-like illness or even severe haemorrhagic fever, which can be lethal.
In South Africa, RVF is expected to be driven by the ongoing La Niña weather event. It enhances summer rains, also in Mzansi’s neighbouring countries, Namibia, Botswana, Zimbabwe, Mozambique and Zambia.
“We have already experienced the joys of good rains, almost countrywide, with the Free State (being) particularly wet and lush. These conditions are ideal for flooding and the formation of pans of water in which Aedes mosquitoes, responsible for the transmission of RVF, breeds and multiplies,” says Oberem.
The well-known veterinarian tells Food For Mzansi that while mosquitoes can transmit the disease to humans, farming and non-farming communities should not be alarmed.
“Yes, mosquitoes do transmit the disease and people do get bitten by them. However, it is a very rare occurrence for humans to be infected by mosquito bites. There are a few cases that have been reported, but it is truly not something to worry about.”
That being said, dead and sick animals to present great danger to the farming sector, warns Oberem.
“Abortions in animals can occur (as a result of RVF) and therefore one must be careful of handling the aborted foetuses. Animals, especially small stock (like sheep, goats and pigs) often die. When farmers, farmworkers or veterinarians who are working with the dead animals make a diagnosis, they get exposed to the virus through the blood and tissue fluids of the dead animals.”
Those handling dead animals must be extremely cautious, especially with animals who have died suddenly and those showing signs of bleeding at death.
“Farmers are therefore advised to vaccinate all cattle, sheep and goats against RVF,” says the department of agriculture, land reform and rural development in a media release. “Live vaccine (OBP Live) must only be used on non-pregnant animals as the live vaccine can cause abortions.”
Government adds that it is the animal owner’s responsibility to vaccinate their animals to death or possible financial losses.
What are the symptoms?
In young animals, signs of infection include fever, failure to eat, weakness, diarrhoea and death.
With older animals, infection may cause fever, nasal discharge, weakness, diarrhoea, excess salivation, vomiting, decreased milk production, loss of appetite and abortion.
Infected humans can not show any symptoms or have a mild illness with fever, weakness, back pain, and dizziness. Only about 10% of humans infected with RVF develop severe symptoms, including eye disease, excessive bleeding, and swelling of the brain.
The recovery rate for humans is generally good, with only 1% deaths recorded. The last case of death was reported on a farm in Jacobsdal in the Free State in 2018.
Prevention is better than cure
Afrivet also recommends urgent vaccination to prevent the virus from spreading and infecting livestock. In addition, farmers can prevent mosquito bites by using products that are registered for the control of mosquitoes. These usually include deltamethrin-containing dips, sprays and pour-ons.
“Ideally, vaccination should have already been carried out in early spring (by December), but it is not too late. However, time is now of the essence as most outbreaks begin mid-to-late summer,” says Oberem.
Onderstepoort Biological Products currently produces two vaccines and Afrivet advises farmers to consider annual vaccination against the disease going forward, saying it is the most effective and easiest route.