West Nile Virus Is an insect borne disease that can symptomatically affect humans and horses. The name comes from the West Nile province in Uganda, where it was first isolated in a human patient with fever. West Nile Virus mostly circulates between birds and mosquitoes without causing disease. Humans and horses are only incidental hosts, meaning that the level of virus in their blood is not high enough to infect mosquitoes. Spread via mosquitoes from one human to another or one horse to another (or horse via mosquito to human and visa versa) does therefore not occur.
The mosquito responsible for transmitting West Nile Virus is found in the vicinity of standing water. Both humans and horses may be infected with WNV but only a smaller percentage becomes clinically affected. About 80% of infected horses never shows any symptoms. Symptoms include stumbling, weak limbs, poor movement, blindness and paralysis. They sometimes even have jaundice. These symptoms may progress to seizures, coma and death. Although they can be treated successfully, up to half of neurologically affected horses die or are euthanised. Fevers are common but not always present. Most humans will have flu-like symptoms such as nausea, fever, headache as well as joint or muscle pain. Less than 1% of patients will develop severe neurological disease There is no cure for West Nile Virus. Treatment consists of symptomatic and supportive care.
Euthanasia should be considered in cases where horses do not respond to treatment and the prognosis is guarded to poor. Can you prevent West Nile Virus or the severity thereof? You can control the vector (mosquitoes) by the application of an effective insect repellent such as DEET. The most efficient way to prevent West Nile Virus is by vaccinating your horse. Even if they do contract the virus, symptoms will be less severe. When should you vaccinate? Foals from the age of 6 months and all naïve adults can be vaccinated. The first vaccination course consists of 2 vaccinations, separated by four weeks. A booster vaccination can then be done annually, a month before the risk period (Summer to Autumn).
Please find attached a lovely article by Dr Caryn Rademeyer – https://www.sava.co.za/vetnews/2016/2023%20June/VN%20CPD%20June%202023.pdf