Every season has its own quota of diseases. Some of them can be treated and eliminated, while others can only be treated symptomatically. Viral diseases are part of the latter group, in which case prevention is better than cure.

This summer, farmers can expect several diseases that are transferred by viruses. Livestock breeders need to be on the lookout for certain disease signs, so that they can act in time.

What is a virus?

According to Dr Jan Blignaut of the Senekal Animal Clinic, it is important to know how a virus works. A virus is a very small infectious deoxyribunocleic acid (DNA) or ribunocleic acid (RNA) organism that multiplies inside a living cell.

Viruses are transmitted in many ways, such as environmental contamination through an animal’s breathing, saliva and other excretions that pollute the environment where other animals can come into contact with it; direct contact between animals, such as scabby mouth, when lambs infect the ewes’ udders; mechanical transfer, such as biting insects; or the use of dirty needles and vectors.

Dr De Wet Barnard of Kranskop Dierekliniek en Wilddienste in Modimolle says it is important to know that a virus differs from parasites, such as those that cause redwater and heartwater, and is also different from bacteria, such as E. coli.

“It isn’t a living organism, as many people understand the term. A virus simply is a collection of cellular components, DNA or RNA, that penetrate other living cells in order to multiply. It means that a virus cannot be killed, which implies implications for their treatment.”

He says one misconception regarding a virus is that it does not transmit a disease. “Rather, it is the disease. It can be something harmless, such as warts, or it can be lethal, such as malignant catarrhal fever. Viruses enter the cells and ‘hijack’ the internal machinery to produce more viruses. The cell then dies, breaks open and the virus spreads further.”

The symptoms caused by the specific virus depend on which bodily cells have been penetrated.

Which diseases to expect

Most viruses are transferred by insects, and in a country with variety of rainfall areas, the occurrence of viral diseases may also differ.

Dr Barnard says viral diseases usually appear along with insects that hatch after the first rainfall. “In sheep bluetongue and scabby mouth are the most common viral diseases farmers can expect. Be on the lookout for Rift Valley fever too, which can also infect humans.

“Common viral diseases among cattle are three-day stiffsickness, lumpy skin disease, malignant catarrhal fever, bovine virus diarrhoea (BVR), infectious bovine rhinotracheitis (IBR), bovine respiratory syncytial virus (BRSV), enzootic bovine leucosis (EBL) and warts.”

Symptoms and treatment

Viral diseases cannot be cured by medication. According to Dr Blignaut, the animal needs to overcome the virus by itself through its immune system, or else it will die. Supportive treatment can relieve the symptoms together with care for the animal during the recovery process.

Certain viral diseases cannot be cured and should rather be avoided or prevented. Therefore, regular immunisation against these diseases is essential.

Producers should be mindful and look out for signs of four of the serious diseases that can be expected this summer, namely lumpy skin disease, three-day stiffsickness, bluetongue and Rift Valley fever.

Lumpy skin disease
The lumpy skin disease virus. (Photograph: The Pirbright Institute)

Symptoms that can be pointed out are fever, loss of appetite, listlessness, decreased milk production, swelling of the limbs and chest, nasal and saliva flow, as well as lumps on the skin and internal areas – hence the name of the disease. LSD is an extremely painful disease and animals often stop feeding and breathe heavily.

Treatment is symptomatic and can include anti-inflammatory medication for the fever and pain, as well as antibiotics for prevention of secondary infections. Vitamin B can help with the recovery process. Isolating animals is of little use, but reusing needles should be avoided at all cost. The best way of curbing this disease is through annual immunisation.

Three-day stiffsickness

Certain symptoms of this disease are unobtrusive. Common symptoms include loss of appetite, apathy, decreased milk production, a nasal discharge, salivation, muscle pains, lameness of one or more legs which sometimes varies and mostly looks like stiffness of movement, and the animals fail to move or they lie down. Other symptoms are a rapid pulse and moisture on the lungs, which can cause secondary pneumonia.

Medical treatment is the same as for lumpy skin disease, such as anti-inflammatory medication for fever and pain, antibiotics for the prevention of secondary infections and vitamin B to help the recovery process. Other ways of assisting are to ensure that animals that are lying down have access to water and soft feed, a dry area to lie down in and enough shelter. It is better to prevent the disease through annual immunisation.

The bluetongue virus. (Photograph: Institute for Molecular Virology)

The common symptoms of bluetongue are high fever, loss of appetite, apathy, loss of milk production and nasal discharge. The animal’s mouth looks dirty as a result of the nasal discharge and salivation. Congestion of the nose, lips, eyelids, ears and face, with even oedema of these parts, can occur.

Other symptoms are ulceration and necrosis of the mouth and tongue, a rapid pulse, moisture in the lungs and hyperaemia of the coronary band of the hoof, sometimes with coronitis and accompanying lameness. Myositis with accompanying muscle tremors and torticollis also occur. Sheep that are ill for longer also have a break in the wool.

Secondary pneumonia can develop, as well as pressure sores if the animal lies down for long periods. Seriously affected animals can die. Symptomatic treatment is the same as above.

Rift Valley fever
The Rift Valley fever virus. (Photograph: RMC Virology)

Lambs and calves are very susceptible to Rift Valley fever. Some of the symptoms are high fever, loss of appetite, apathy, abdominal pain, bloody diarrhoea and jaundice. It can also lead to sudden death.

Symptoms that can occur in cows are fever, a dull coat, loss of appetite, severe salivation, lacrimation, apathy, lower milk production, foul smelling diarrhoea and abortions.

Symptoms in ewes are high fever, loss of appetite, apathy, weakness, depression, fast breathing, purulent nasal discharge, vomiting and smelly, bloody diarrhoea. Abortions often occur.

Other viral diseases

Dr Barnard points out that there are more viral diseases to take note of, notably malignant catarrhal fever, IBR and BRSV which can easily cause discharge from the nose and eyes. The bovine leucosis virus exhibits no symptoms in most cattle, but can cause cancerous tumours in certain animals. EBL is often accidentally detected in laboratory tests.

Viral and bacterial diseases can easily be confused and a diagnosis will depend on the history of the herd, the environment, symptoms and blood tests. His advice is to rather consult the veterinarian every time. It is also advisable to compile a suitable farm- and area-specific immunisation programme together with the veterinarian.

“Some basic management principles apply with regard to insect-borne sheep viruses. If possible, sheep should be kept in high-lying areas away from standing water – especially at night. Animals must be dipped to protect them against flies and mosquitoes,” he says. – Koos du Pisanie, Stockfarm

For more information, phone Dr Jan Blignaut on 083 449 4566 or Dr De Wet Barnard on 014 717 5996.