(Warning: Article contains visuals that might upset sensitive readers.)
The outlook for the rainy season over large parts of South Africa is perfect for many animal diseases. These conditions are driven by a likely shift from El Niño to a neutral or La Niña state. While the eastern parts of the country may see above-average rainfall from late spring into early summer, some central and western areas might start with average to below-average rainfall before potentially improving from December onwards.
This positive outlook for rain, warns well-known veterinarian and former CEO of the Ruminant Veterinary Association of South Africa (RuVASA), Dr Faffa Malan, unfortunately carries a high risk for several animal diseases. It is therefore important that livestock producers take timely precautions. Most of the diseases, he points out, are vector-borne, meaning they are transmitted by mosquitoes, midges, or ticks. Some are also zoonotic, which means that they can be transmitted to humans.
Rift Valley Fever
Rift Valley Fever is a viral disease transmitted by mosquitoes, mainly Aedes and Culex spp. The last heavy outbreak of Rift Valley Fever was in 2010. Many producers have not kept up their vaccination programme, which caused a large population of sheep, especially lambs, goats, and cattle, to be susceptible to the disease.
Heavy or prolonged rainfall causes hatching of infected mosquito eggs from dormant stages in flooded pans. The disease causes fever, abortions, jaundice and sudden deaths, especially in young animals. Being a zoonotic disease, it also poses a serious public health concern.
Prevention consists of vaccination, preferably before the rainy season and vector control by keeping animals away from flooded plains.
Bluetongue
Bluetongue is a viral disease in small stock transmitted by Culicoides midges. Warm, wet weather is ideal for midge populations to thrive. The symptoms are fever, swelling of the face and tongue, lameness, and death in severe cases.
Prevention consists of vaccination before midge numbers increase and avoiding low-lying wet camps.
African horse sickness (AHS)
AHS is a viral disease in horses, donkeys, and mules – also transmitted by Culicoides midges. The virus thrives in prolonged wet periods that extend the midge breeding season.
Prevention consists of a strict vaccination program and stabling animals during peak midge hours.
Heartwater (Ehrlichia ruminantium)
Hearwater is a tick-borne disease, mainly transmitted by the bont tick, Amblyomma hebraeu. It is triggered when tick populations explode during warm, humid conditions. It affects cattle, sheep, and goats – especially exotic or non-adapted breeds.
Prevention consists of strategic tick control, prophylactic treatment in high-risk areas, and the use of resistant breeds. A blood vaccine is available: contact your veterinarian for the use of the vaccine.
Babesiosis (redwater)
“Redwater” is the farmer’s name for bovine babesiosis, a tick-borne disease caused by Babesia protozoa that invade and destroy red blood cells. In South Africa, we distinguish between African Redwater and Asiatic Redwater, depending on the species involved:
- African Redwater is caused by Babesia bigemina, transmitted mainly by the blue tick (Rhipicephalus decoloratus). It tends to cause a somewhat milder, slower-developing form of the disease.
- Asiatic Redwater is caused by Babesia bovis, transmitted mainly by the southern cattle tick (Rhipicephalus microplus). This form is more severe, often with nervous signs (staggering and collapsing) due to blockage of small blood vessels in the brain.
Both forms cause fever, anaemia, weakness, and red or dark-brown urine, but B. bovis infections progress faster and kill more animals if not treated quickly.
Prevention depends mainly on tick control. Dip regularly and manage grazing to reduce tick habitat.
Blood vaccines are available; contact your veterinarian for information on how to use these vaccines.
Anaplasmosis (gallsickness)
Anaplasmosis is a tick-borne disease of cattle caused by the rickettsia Anaplasma marginale. The organism attaches to the surface of red blood cells, causing the animal’s immune system to destroy them — leading to progressive anaemia, weakness, and jaundice. It spreads mainly through blue ticks (Rhipicephalus decoloratus and R. microplus), but can also be transmitted by biting flies or contaminated needles.
The disease tends to appear a few weeks after heavy rain when tick numbers peak. Treatment with long-acting oxytetracycline or imidocarb is effective if started early, but prevention through tick control, vaccination, and good biosecurity remains the best strategy.
Three-Day stiffsickness
Three-day stiffsickness is a viral disease of cattle transmitted mainly by mosquitoes and biting insects. It tends to break out after the first good rains when these insect vectors multiply. It can cause major temporary losses through reduced milk yield, weight loss, and infertility in bulls.
Vaccination is recommended before the rainy season. Provide shade, soft soil, and water for affected animals to ease discomfort.
Lumpy skin disease (LSD)
LSD is a virus transmitted by biting insects (flies and mosquitoes). High rainfall and humidity favour vector breeding and cattle are specifically affected. It can be prevented by annual vaccination before the rainy season.
Anthrax
Anthrax is caused by a bacterium, Bacillus anthracis spores in soil. Heavy rains after drought can bring spores to the surface – as currently seen in the outbreak on the Ghaap Plateau in the Northern Cape – and affect cattle, sheep, goats, wildlife, and humans. Prevention is by annual vaccination.
Foot rot
Foot rot is caused by bacteria and triggered by persistently wet and muddy conditions. It mostly affects sheep, but goats and cattle can also contract the disease. Prevention measures include foot baths, proper drainage, and pasture rotation.
Internal parasites
A wet summer brings a surge in internal parasites. Warm, moist conditions after early rains create perfect development of worm larvae on pastures. When the first green flush follows winter, sheep return to grazing camps that may still carry last season’s larvae.
Ewes around lambing time are especially vulnerable, as their temporary loss of immunity allows worm burdens to increase sharply, contaminating the pasture even further. Lambs pick up heavy infections early in the season, and the cycle continues.
The most common internal parasites associated with wet conditions include wireworm, brown stomach worm and, in marshy or waterlogged areas, infected water snails are the intermediate hosts for liver fluke.
Worm resistance to deworming treatments is one of the most serious long-term threats to effective parasite control. Over years of frequent or routine dosing – especially when the same product or chemical group is used repeatedly – resistant worms survive treatment and pass that resistance on to their offspring. In many parts of South Africa, Haemonchus contortus (wire worm) populations are now resistant to three or more major drench groups.
To slow resistance, farmers should rotate actives, dose only animals that need it (using tools like the FAMACHA card or faecal egg counts), and always use the correct dose for the animal’s weight. Strategic treatment, combined with good grazing management, is the only sustainable way to keep modern drenches effective for the future.
“Now is the time to be aware of clinical signs caused by diseases transmitted by insects, ticks, and internal parasites,” Dr Malan warns. “Every farmer should have a thermometer, as the first sign of an infectious disease is a rise in temperature. Blood smears can be taken and examined by your veterinarian to confirm African and Asiatic redwater and anaplasmosis.
“Your veterinarian should be your first contact if an animal dies. A postmortem and capturing images with your cell phone can greatly help in diagnosing the issue and preventing further losses. Update your vaccination programme if necessary.” Prevention is better than cure. – Izak Hofmeyr, Plaas Media
