West Nile virus is a mosquito-borne virus that causes disease in humans and animals. After previous outbreaks in Africa, the US, Italy, Austria and Germany, RIVM announced in September 2020 that West Nile virus (WNV) had also been found in the Netherlands. Humans and horses can become infected if they are bitten by an infected mosquito. Preventive measures for horses consist of vaccination and prevention of mosquito bites.
Symptoms
A West Nile infection in the horse can be completely asymptomatic, but can also cause general symptoms such as fever, lethargy, not eating or some light colic. Sometimes neurological symptoms such as muscle tremors, ataxia and behavioral changes can also occur. In the worst case, horses become paralyzed and die or have to be euthanized.
Diagnosis & Treatment
West Nile virus can be diagnosed by blood tests. There is no specific therapy for West Nile virus. If a horse becomes ill, it can only be helped with support.
Diffusion & prevention
West Nile virus spreads through infected mosquitoes. Horses and humans are so-called definitive hosts, which means that they never get so much virus in their blood that they are infectious to another via a mosquito. Preventive measures for horses consist of vaccination and prevention of mosquito bites.
Mosquito bites can be prevented, for example, by using insect repellents and fly blankets. It is also wise to prevent stagnant water, which is a good breeding ground for mosquitoes, as much as possible.
Vaccination
Vaccinations can be given from 5-6 months of age. The first time a basic vaccination must take place, 2 vaccinations with 3-6 weeks in between. Thereafter, the vaccination should be repeated annually, preferably just before the mosquito season (in April/May) so that horses are protected during the most critical period in August/September. Protection is achieved 2-3 weeks after primary vaccination. It is possible to vaccinate an individual horse in a stable. It is not necessary to vaccinate the entire house, as is the case with other vaccinations against influenza, for example. The horse is protected by vaccination. The horse can still get sick, but the disease process is less intense. There is no vaccine available for humans.
Advice
Previously, the advice was to vaccinate a horse if it goes abroad or is valuable (emotionally or financially). It is now known that the West Nile virus has also been found in the Netherlands and it is possible to protect your horse. Consult with your vet what is sensible in your case.
Click here for an overview of frequently asked questions and answers about the West Nile virus.