Concern prevails over a possible outbreak of Rift Valley Fever following high rainfall in production areas over the course of the year. An outbreak of this nature will have serious repercussions for the cattle industry.
“We already had quite a lot of rain showers across the whole of South Africa over the last couple of weeks. In various areas within the summer rainfall region there are large pans of water,” says the National Animal Health Forum (NAHF).
According to the NAHF, it could become dangerous if insects start to move to where there are animals that have never had contact with the disease and are therefore vulnerable.
Dr Stuart Varrie, a vet adviser at Cape Wools, explains that South Africa is ripe for another outbreak of the disease. It is especially worrying that it could happen during this current season.
He says that vaccinations can efficiently combat the disease whilst also mitigating the effects thereof. Responsible cattle farming can thus prevent economic adversity.
Widespread outbreaks of the disease were recorded in South Africa between 2008 and 2011. In 2010 and 2011 at least 14 000 animals were infected during outbreaks in eight of the nine provinces. Many cases were, however, most likely never recorded. In total 302 cases of the disease were recorded in humans, along with 25 deaths.
He says that factors that increase the risk of an outbreak include the good and widespread early summer rains across large parts of South Africa. If this continues, it could lead to flooding and the formation of water pans that present the ideal breeding ground for the Aedes mosquito that carries the Rift Valley Fever disease.
Furthermore, Rift Valley Fever is almost always present in South Africa, which further increases the risk of an outbreak.
After the outbreak in 2010, there has been an active effort by livestock owners to vaccinate their livestock and high vaccination levels were maintained. Over time, vaccinations began to decrease, meaning that there are increasingly more unprotected and under-protected animals that have no or insufficient immunity against the disease.
“Remember, the concept of herd immunity spoken about for Covid-19 indicates that in order prevent an outbreak, you need 70% of a population to gain immunity.”
“The abovementioned represents the perfect storm for the disease to turn an inter-epizootic period into a full-blown epizootic outbreak with devastating consequences.”
The NAHF encourages farmers to vaccinate their cattle. According to the NAHF, it received many enquiries over the last couple of months regarding the availability of OBP’s live and inactivated vaccinations. It appears as though farmers are eager to vaccinate their cattle.
“They are eager to get their hands on vaccinations but have not always been able to get hold of the inactivated vaccinations.”
Recently, OBP announced that live and inactivated vaccinations are available again. The shortage can be attributed to a freeze-drying machine at the laboratory that was out of order, which had to be repaired by an international expert. The machine has since been repaired.
The ins and outs of an outbreak
For an outbreak to occur the climate needs to be favourable for the number of vectors to increase. Initially, the infection of the virus to receptive host populations will be limited due to a few animals which would initially be carrying the disease, despite there being more mosquitos. Due to the hosts’ low immunity levels, however, the virus will increase rapidly in both quality and quantity.
The increased number of viruses in the blood will serve as a source of the virus from which uninfected mosquitos become infected when they feed on the animals. After this, the infection of other receptive hosts increases considerably due to the newly infected vectors and the whole cycle will then repeat itself.
According to Varrie, the disease is a huge problem. “It kills animals, causes abortions, and makes the animals very sick whilst many of those that survive are never able to recover to their full potential.”
It is also a very serious zoonosis that is easily transferred from animals to humans, with symptoms ranging from relatively light to death in humans. Transfer occurs when people treat sick animals and come into contact with the remains, blood or raw meat of infected animals. Almost all cattle species can be infected with sheep usually being more at risk than cows and goats, but even buffalo can be infected.
Anyone who wants to learn more about the disease can visit the NAHF’s webpage at https://nahf.co.za/?s=Rift+Valley+Fever, the FAO at https://www.fao.org/common-pages/search/en/?q=Rift%20Valley%20Fever and the Eco Health Alliance-group, of which the NAHF are members, at https://www.ecohealthalliance.org/program/rift-valley-fever – Fredalette Uys