| Information sheets | | | Elsenburg infopaks | | | Animals, diseases: 13 |
Rift Valley and Wesselsbron
Afrikaans | Xhosa
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Rift Valley fever is a contagious disease of sheep, goats and cattle.
Dogs and cats can also get ill if they eat contaminated meat.
The disease is caused by a |
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virus which is transmitted by mosquitoes. Outbreaks usually occur from spring until late in summer.
It is very important to be aware that humans can also contract the disease if they work with sick animals or contaminated meat. Mosquitoes play no part in the transmission of the disease to humans. |
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Contracting the disease can result in death due to damage to the liver, or blindness. The disease originated in the Rift Valley region of East Africa, and occurred for the first time in South Africa during the nineteen-fifties.
Twenty thousand people became ill, and some 100,000 sheep and cattle died. At the next outbreak during 1974/75 even more people and animals were affected. |
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Symptoms of the disease
Up to 95% of pregnant animals may abort. For animals to die is commonplace. Among young lambs and calves mortality can be as high as 95%. Older animals offer more resistance, with a mortality rate of about 25%. Death among young animals is swift, and occurs without visible signs. Older animals stop grazing, become weak, and are left behind by the flock. They may present with bleeding of the nose and bloody diahoerrea, while the eyes and skin may show a yellow hue. |
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Goats have a greater resistance to the disease, and their symptoms are less severe. |
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Post-mortem signs
The disease is characterised post mortem by bleeding occurring in various organs. |
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Bleeding in the heart, lungs, liver and gall bladder is particularly noticeable. |
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Free blood may occur in the chest cavity. |
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The linings of the rumen, |
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abomasum and |
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intestines also often show characteristic bloody streaks. |
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Liver damage also occurs. The liver may be distended, with a yellow to orange hue. |
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Pinhead-sized gray-white specks can be observed
everywhere in the liver where cells have died.
When a person has had contact with a carcass of this nature it is necessary to wash him or her thoroughly to avoid infection. |
Prevention
In sheep and goats a live Rift Valley Fever vaccine can be used, which would immunise the animal for life. It is very important to bear in mind that a pregnant animal must not be vaccinated, because both the ewe and the unborn lamb may die. For pregnant sheep and goats the dead Rift Valley Fever vaccine is used. This vaccine protects the animal for only one year. For cattle only the dead vaccine is recommended, and here too it provides protection for only one year.
Wesselbron disease is very similar to Rift Valley fever, and it can often be distinguished only in the laboratory. Moreover, it often co-occurs with Rift Valley fever. The symptoms are very similar, but are not as deadly. Abortions are very common, but humans are not affected. Only a live vaccine is available, which can be used in conjunction with the live Rift Valley vaccine. However, it can not be used for pregnant animals.
AO de Kock
ELSENBURG / VREDENDAL Veterinary Services
