By Dr ‘Mac’ Mc Farlane, State Veterinarian, Graaff Reinet
The Rift Valley Fever virus has been spreading across South Africa for two years, and good rainfall in the coming summer is likely to cause this disease to re-emerge, with serious consequences for the country as a whole.
An epizootic of RVF can generally be seen in years of unusually heavy rainfall and localised flooding. The excessive rainfall allows mosquito eggs, usually of the genus Aedes, to hatch. The mosquito eggs are naturally infected with the RVF virus, which is then transferred to the livestock on which the mosquitoes feed. Once the livestock is infected, other species of mosquitoes can become infected via the animals and spread the disease even further. The virus can also be transmitted by other biting insects.
The farming community can play a major role in limiting the number of RVF outbreaks if proper action is taken to immunize animals over the next few months, before natural conditions become conducive to spreading the disease again.
Those most at risk of contracting RVF are farmers, farm workers, slaughterhouse personnel and veterinarians and their assistants.
Some farmers believed that goats would not be affected. However, certain outbreaks affected only goats, while others affected mainly cattle. It is therefore essential to vaccinate all goats, cattle and sheep before the end of spring.
The live vaccine, which gives the best immunity, is available from Onderstepoort and other outlets. It should not be used on pregnant sheep or goats, however. If you have never vaccinated in the past, you can inoculate lambs and kids from one month onwards, as there is unlikely (at that stage) to be maternal/ colostrum antibodies to interfere with the vaccine.
Precautions and symptoms
Precautions should be taken if you suspect you have RVF on your property, and your veterinarian or local state veterinary office should be contacted for advice and assistance, as RVF is a notifiable disease. Farmers and labourers should take extra precautions when dealing with suspect animals. Protective clothing, i.e. full overall, face mask, gloves and gumboots, should be worn when dealing with such cases. The post mortem material is infective, but due to decomposition, the Ph of the material changes, very quickly destroying the virus. Even so, it is advisable to bury or burn infected carcasses.
RVF is an extremely virulent virus and there is no known treatment for it. Those with a challenged immune system are especially vulnerable. In humans, the disease manifests with flu-like symptoms including photophobia (sensitivity to light) and severe headaches that could develop into encephalitis. As with most viruses, one’s own immune system offers the best resistance against the disease. The virus lasts for four to seven days, and full recovery is possible. Bear in mind that some RVF complications may only manifest a few weeks after the acute infection.
Mohair and wool exports to China have suffered because of the fact that the veterinarians at ports of export have to sign a document stating that there has been no RVF in the district in question for 12 months. Since most districts in SA have been affected by RVF, China has declared a total, year-long ban on raw wool and mohair from South Africa. A deputation has been sent to China to impress upon the Chinese Government that RVF cannot be spread via wool or mohair fleece. Should the deputation be unsuccessful, there are bound to be serious consequences for our export market.
Do your share by taking measures to prevent RVF from occurring or spreading: Vaccinate all your animals as soon as possible!