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- Malignant catarrhal fever or snotsiekte is responsible for the death of thousands of head of cattle in South Africa every year. This deadly viral disease is transmitted to cattle by wildebeest.
- The mucous that builds up in cattle’s respiratory tracts leads to laboured breathing, and these animals eventually suffocate on their own mucous. It can even cause pneumonia.
- The airborne virus can travel up to a kilometre, which means that contamination can theoretically occur when a truck transporting wildebeest drives past a herd of cattle. Dr Kobus Grobler, a veterinarian from Bergbos Animal Clinic in Rustenburg, says although few animals in a herd will become sick, it is almost always fatal.
- The first visible signs of the disease are seen two to four weeks after contact with the virus. Animals, however, can still become ill up to seven months after having been exposed.
- To confirm that the snotsiekte virus is indeed present in an animal, a blood culture can be performed, or it can be confirmed by conducting modern DNA tests.
Malignant catarrhal fever or snotsiekte is responsible for the death of thousands of head of cattle in South Africa every year. This deadly viral disease is transmitted to cattle by wildebeest. Characteristic of this disease is the purulent nasal and eye discharge caused by a herpes virus.
Both types of wildebeest can carry the virus responsible for snotsiekte in cattle. Blue wildebeest, however, are the main source of disease spread, simply because there are significantly more blue than black wildebeest.
Wildebeest release large numbers of the virus when they experience stress. When wildebeest calve or are captured and transported, virus numbers build up in the animals, are released through their respiratory tracts, and vulnerable cattle are infected. There are no known cases of other game species that have contracted the disease.
The mucous that builds up in cattle’s respiratory tracts leads to laboured breathing, and these animals eventually suffocate on their own mucous. It can even cause pneumonia.
Read more about respiratory diseases and feedlots here.
Spread of the virus
The airborne virus can travel up to a kilometre, which means that contamination can theoretically occur when a truck transporting wildebeest drives past a herd of cattle. Dr Kobus Grobler, a veterinarian from Bergbos Animal Clinic in Rustenburg, says although few animals in a herd will become sick, it is almost always fatal.
The nasal and eye secretions of two- to three-month-old wildebeest calves contain large amounts of the virus; it is during this period that cattle kept in the vicinity of wildebeest are most vulnerable.
Infected cattle do not usually transmit the virus to other cattle, but in-calf cows can infect their calves – these calves usually succumb before they are six weeks old.
Clinical signs
The first visible signs of the disease are seen two to four weeks after contact with the virus. Animals, however, can still become ill up to seven months after having been exposed.
Infected animals initially exhibit a watery eye and nasal discharge, which soon become excessive and turn purulent. The nasal surface becomes dry, sores develop and the purulent nose discharge forms a hard crust that clings to the nostrils.
Infected animals often breathe through their mouths because of the excessive amount of discharge in their nose. The mucous membrane in the mouth is red with sores on the inside of the lips, on the gums, on the palate and on the underside of the tongue.
The conjunctiva of the eyes is very red and inflamed, and the cornea is dull. Inflammation of the cornea develops from the outside to the inside.
In some cases, infected animals may present with bloody diarrhoea, inflamed skin between the claws, enlarged lymph nodes and nervous symptoms. In terminal cases, hypersensitivity, muscle and eye tremors, and convulsions may occur.
Post-mortem examination
A post-mortem examination will reveal a lot of pus in the nasal cavities, with the tissue of these cavities often necrotic. The mucous membrane in the mouth, oesophagus, rumen and sometimes the small and large intestine will be full of sores. Small haemorrhages are visible in the trachea and there may be signs of pneumonia. The liver is often enlarged and when dissected will have numerous light-coloured spots. The lymph nodes are enlarged, very red and watery.
The wall of the bladder may be full of sores, and the kidneys can be swollen and feature several white specks. Other signs include widespread bleeding, as well as areas where the blood supply to the kidney tissue has been cut off. This is revealed when the kidney is dissected. The meninges may also be very red, indicating meningitis.
Confirm with analysis
To confirm that the snotsiekte virus is indeed present in an animal, a blood culture can be performed, or it can be confirmed by conducting modern DNA tests.
The preferred method is to draw blood into an EDTA tube (with the purple cap) before the animal succumbs. The blood must then be kept on ice and sent to a laboratory as soon as possible. The tissue of dead animals, especially the brain, lymph nodes, spleen and eye, can be placed in formalin and sent to a laboratory for analysis.
There is no vaccine available against snotsiekte in South Africa. A license agreement was signed between Onderstepoort Biological Products and the Moredun Research Institute in Scotland to further develop, register and manufacture their vaccine in South Africa. However, this vaccine is not yet commercially available.
Dr Grobler says the best way for a producer to keep his or her cattle herd disease free is to prohibit any contact between the herd and wildebeest, especially during the calving period or when wildebeest are being handled in a way that elicits a stress response.
Cattle must be kept at least 500m, but preferably 1 000m, away from wildebeest. – Andries Gouws, Plaas Media
For more information, email Dr Kobus Grobler at kobus@bergbosvet.co.za.
