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- Redwater remains a pressing issue, especially in South African cattle herds, says Dr Hanri Bester-Cloete, state veterinarian at the Bloemfontein Provincial Veterinary Laboratory.
- The parasites enter the animal’s bloodstream via the bite of an infected tick.
- African redwater, she explains, is the slower form of the disease – animals take a few days before exhibiting signs of infection such as high fever (above 40°C), lethargy, loss of appetite, pale colour, jaundice and red urine.
- According to Dr Bester-Cloete, it is crucial to control ticks in herds without previous exposure, such as newly purchased animals.
- A vaccine against redwater does exist but is expensive, and its availability is not always guaranteed.
Redwater remains a pressing issue, especially in South African cattle herds, says Dr Hanri Bester-Cloete, state veterinarian at the Bloemfontein Provincial Veterinary Laboratory. Outbreaks can even persist in regions in which the disease has been present for many years and animals have built up resistance – this is particularly the case if conditions are stressful or newly purchased animals are introduced.
The Northeastern Free State experienced a major outbreak two or so years ago after an intense heat wave – the high temperatures led to stress and suppressed the animals’ immune systems.
Redwater affects any breed or age. Calves as young as two to three days old contracted the disease, although the dams exhibited no symptoms; deaths were recorded in four-month-old calves. It is not limited to summer; redwater cases have recorded in June and July, even in the country’s colder regions. It is especially prevalent in South Africa’s northeast, but more common in the warmer north.
Figure 1: African redwater, April 2022 to September 2024. (Source: www.rmis.co.za)
Causes of redwater
The protozoan Babesia is responsible for redwater, explains Dr Bester-Cloete. It is species-specific and each Babesia species is found only in one animal species. Two species of Babesia are of importance in Southern Africa: Babesia bigemina, which causes African redwater and is transmitted mainly by the blue ticks Rhipicephalus (Boophilus) decoloratus and R. (B.) microplus; and Babesia bovis, which causes Asiatic redwater and is transmitted by the Asiatic blue tick R. (B.) microplus.
The parasites enter the animal’s bloodstream via the bite of an infected tick. They invade the red blood cells, multiply – first from one to two, and then from two to four – and cause the cell to rupture.
Each released parasite then attacks a new red blood cell, multiplies within it, and ruptures the cell, resulting in anaemia and possible death. The animal launches an immune response during which it attempts to break down the infected red blood cells to fight the infection. However, the parasites affect the clotting factors, which can lead to organ failure.
Read more about Why dip cattle if we see no ticks?
Signs of redwater
African redwater, she explains, is the slower form of the disease – animals take a few days before exhibiting signs of infection such as high fever (above 40°C), lethargy, loss of appetite, pale colour, jaundice and red urine. Early treatment can be effective. Asiatic redwater is more aggressive and may lead to animals succumbing without visible signs being present, often without red urine and sometimes accompanied by nervous symptoms which makes the animal more aggressive. The entire herd must be treated if several animals suddenly die.
According to Dr Bester-Cloete, it is crucial to control ticks in herds without previous exposure, such as newly purchased animals. Pour-on or spray-dip products are more effective than injectable products, in which case the tick must bite the animal for the product to be absorbed. The bite can transmit the parasites.
Monitor sick animals daily. In herds in which redwater has been present for several years, tick control is still important but not vital. It remains important to provide vitamins, good nutrition and clean water to strengthen the immune system.
Upon encountering a sick or dead animal, the veterinarian should make a rapid diagnosis, often via a blood smear. Treat the entire herd with diminazene or imidocarb if an outbreak is suspected. Even if the herd has 400 cows, it is best to treat them rather than losing more animals.
Immunity to redwater
A vaccine against redwater does exist but is expensive, and its availability is not always guaranteed. It is effective for vaccinating valuable animals, such as herd or stud bulls. The logistics involved in transporting and administering this vaccine present certain challenges, as it must be kept on dry ice and be administered intramuscularly immediately upon thawing. Animals should be monitored daily, or even twice daily, after vaccination.
Dr Bester-Cloete encourages producers to work alongside their veterinarian to determine whether vaccination is feasible. Alternative approaches such as farming with nature are usually a good option. Alternatively, tick control, good condition and natural exposure to the disease can also help build immunity.
Send an email to Dr Hanri Bester-Cloete at vetlabbloem@gmail.com for more information.
