West Nile Virus

West Nile Virus
31 May, 2012
– Dr Jenny Lawrence

What Is It?

West Nile Virus is a viral disease that causes neurological signs. It is transmitted by mosquitoes and is carried by wild birds, crows are known to die from the disease. Like Horsesickness, it is not a contagious disease. Humans can be infected by the disease if bitten by infected mosquitoes but cannot be infected by horses with the disease, unless they are performing a post mortem. This disease generally occurs in the warmer months of the year when mosquitoes are most prevalent.

Clinical Signs:

Not all horses become clinically ill. The virus attacks the central nervous system and causes encephalitis. The clinical signs can vary from very mild to coma and death. The horses with the mild form of the disease have a fever, are listless and have a loss in appetite. The more severe cases show ataxia, circling, depression, weakness and in the most extreme cases convulsions, coma and death. The severe clinical signs can be confused with Neurological Herpes, Botulism and Rabies and the mild cases can be confused with any disease that causes listlessness and a fever.

Image: Bosch Hoek Equine Hospital


Blood samples taken in EDTA tubes and samples of brain and spinal cord from post mortem are used to diagnose the disease. As this disease can look like many other diseases it is advisable to also do a complete blood count.


There is no specific treatment for this disease, only symptomatic and supportive care. This is aimed to reduce the discomfort, pain and inflammation and to reduce secondary bacterial infections and keep the horse hydrated. The more severe cases can become costly to treat as they are often recumbent and need intensive nursing care to minimise secondary muscle damage and ‘bed sores’. These horses often need to be put in a sling which can be costly to erect. It is important to keep stress to a minimum and protect the patient from adverse weather conditions.


Horse in a sling. Note the padded walls too. Image: Bosch Hoek Equine Hospital

Majority of horses with WNV show mild symptoms and recover rapidly. Neurological signs are infrequent and if well supported these horses recover well. Coma and death from the disease is rare.


As with the midges, preventing the mosquitoes from biting the horse is the best form of prevention. This includes using insecticides on the horse and in the stables, stabling between dust and dawn, removing stagnant water and turning lights off in the stables at night. Drug companies are looking at importing a vaccine in the near future.

Bosch Hoek Equine Hospital is a state of the art Equine hospital situated in the beautiful Kwa-Zulu Natal Midlands of South Africa. Our primary goal is to offer clients and their horses world class care and expertise for both surgical and medical conditions with a rehabilitation centre to match.

If you require our services or would like to discuss anything please call one of us on the numbers below:

Dr Helen Tiffin 082 966 9324
Dr Jenny Lawrence 082 836 9897
Dr Anna Bowker 082 849 3456 (away until August)
Dr John Hodsdon 072 165 7122

Dr Jenny Lawrence
Equine Veterinarian BVSc

Jenny qualified in 2005 after which she worked as a small animal veterinarian in the United Kingdom for 3 years. In 2008 she returned to South Africa to begin equine work with the late Dr Dave Mullins before joining the Bosch Hoek Equine Hospital where she has become an important part of our team and has a special interest in foal medicine. Jenny recently returned to the UK for a short period where she worked with renowned breeding expert, Dr Jonothan Pycock as well as spending time at various equine hospitals and AI centres in the UK.

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