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Since the last report in November heavy downpour with flooding occurred in many areas of South Africa. Water sources (water pans, dams, vleis) are filled to the brim and midges and mosquitoes, the transmitters of viral diseases such as Blue Tongue, Rift Valley Fever, Wesselsbron Disease, African Horse Sickness, Ephemeral Fever and Lumpy Skin Disease, West Nile Fever, Akabane have been reported.
Indeed, the current circumstances do appear very favourable for the occurrence of RVF. In our study area in Western Free State in 2015/16, i.e., about 5 years after the last large RVF epidemic, the overall seroprevalence in domestic ruminants was estimated at 30% (43% in cattle, 28% in sheep, 9% in goats). But this would have included many animals naturally exposed during the outbreaks. Two years later it had dropped somewhat. I’m not sure many farmers have been vaccinating much since then, so we likely have a largely susceptible population again. Mosquito numbers are currently very high – we just don’t yet know whether the virus is around…
Are many farmers vaccinating, or trying to obtain vaccine?
In 2010 a huge outbreak of Rift Valley Fever occurred in South Africa.
Information shared by the EcoHealth Alliance is that at present similar ecological conditions exist when compared to conditions that existed during the huge Rift Valley Fever outbreak during 2009 to 2011. See the seasonal rainfall forecast from our NASA Team.
In summary, at 50mm excess rainfall/season with a peak in rainfall in January we are approaching similar conditions recorded during the 2009-11 outbreak!
In our publication: “Climate conditions during a Rift Valley fever interepizootic period in Free State, South Africa (submitted); the epizootic period had excess rainfall on the order of ~+ 367.50mm. This equates to a monthly excess of anywhere between 22 – 52mm with rainfall peaks in January as opposed to the interepizootic peaks recorded in February and April.
Farmers are pre-warned to be on the lookout for clinical signs of Rift Valley Fever (Slenkdalkoors) such as abortion storms.
The OIE has given the following summary of the disease:
Rift Valley fever (RVF) is an acute arthropod-borne viral disease that can cause sever disease in domestic animals, such as buffalo, camels, cattle, goats and sheep. RVF is also an important zoonosis that can cause disease in humans. Outbreaks have been reported in Sub-Saharan Africa and Egypt.
Disease in susceptible animals can vary in severity and is characterized by fever, listlessness, anorexia, disinclination to move, abortions and high morbidity and mortality rates in neonatal animals. RVF is an OIE listed disease as indicated in the Terrestrial Animal Health Code Chapters 1.1 and 8.15. Because of its long inter-epizootic intervals, it is also regarded as a re-emerging disease.
https://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/3.01.18_RVF.pdf
RVF is transmitted by mosquitoes. What is the risk that your animal will be bitten by an infected mosquito!? Were your animals vaccinated once in their life-time with the live, attenuated, Smithburn vaccine?
- During an outbreak, only vaccinate animals with the inactivated vaccine! Pregnant animals should not be vaccinated with the live vaccine.
- Move animals to high areas of the farm away from water sources. Spray animals with insecticides.
- As this is a serious zoonosis avoid handling infected carcases and afterbirths!!
Reports of diseases transmitted by ticks (African and Asiatic red water; Anaplasmosis; Heartwater, Lumpy skin disease and Sweating sickness) have been received. Tick damage especially to the udders of cows could cause great economic loss to farmers.
Wireworm outbreaks have been reported from 8 provinces. Make sure to discuss your management program with your veterinarian as resistance of this deadly internal parasite to drug groups may cause huge losses.
Diseases that are reported every month are Brucellosis, Trichomonosis, Vibriosis, Cryptosporidiosis, Orf, Pasteurellosis, E. coli, Pulpy kidney.
To assess your risk, talk to your local veterinarian and update your vaccination and holistic parasite management program. Visit the Ruminant Veterinary Association of South Africa’s website (www.ruvasa.co.za) and click on Disease reporting to see what diseases are prevalent in your area. Take the necessary steps in time, as from experience it is seen that vaccine availability during an outbreak could be a huge problem. If vaccines are not available insect and tick control are of utmost importance.
Visit the National Animal Health Forum’s website regularly where updates on animal health are posted (www.nahf.co.za).
CONTACT YOUR LOCAL VETERINARIAN!
The information provided in this article is supplied by Prof. Peter Thompson, an epidemiologist. To contact him please email him at peter.thompson@up.ac.za or contact him on +27 12 529 8290.
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