West Nile virus (WNV) is one of the equine arboviral encephalitides and as such, can cause encephalitis (a serious nervous disease) in horses, which can be fatal. Wageningen Bioveterinary Research conducts research on this disease.
The West Nile virus is caused by a flavivirus, which can infect many bird and mammal species, among which humans and horses.
Wat is West Nile Virus?
West Nile Virus (WNV) is a virus transmitted by insects (arbovirus) belonging to the genus Flavirus in the family Flaviviridae. Two groups (lineages) of the virus are distinguished on the basis of their genetic relationship. WNV causes the disease West Nile Fever (WNF).
Infection with the West Nile Virus
West Nile Virus is spread primarily by the mosquitoes of the Culex family. These mosquito species occur across the whole of Europe, but infections are mainly reported in warmer Southern Europe. WNV propagates primarily in birds, which in this way form a source of virus transmission. Many other vertebrates, among them mammals including horses and humans, can be infected. Approximately 10 to 20 per cent of these infections lead on to symptoms, and only a very small proportion (1 per cent) progress to becoming very serious. Infected mammals are 'dead-end hosts', i.e. too little of the virus is produced for further transmission.
Transmission of the disease
The disease originally occurred only in Africa. Transmission has expanded, particularly over recent decades, to regions that were previously free of the disease, and it has become endemic in regions around the Mediterranean Sea, India and Central and South Africa. Most worthy of note is the introduction into The Bronx, part of New York City in the United States.
Infections were first reported in Germany in 2018. WNV poses a serious threat to the health of humans and animals. Wageningen Bioveterinary Research (WBVR) is watching the situation closely and is in consultation with Dutch institutes to prepare for the possible arrival of the virus.
Any suspicion of this notifiable disease must be notified to the national government and the European commission.
WNV was first encountered in the United States in 1999. Its spread across the entire continent over subsequent years forms a recent example of extremely rapid dissemination following initial introduction to a new region. It turned out over the years that WNV had definitively established itself on the continent. The virus probably entered New York via infected birds.
WNV first manifested in high mortality in the crow population. Humans and horses were subsequently infected, causing a great deal of sickness and even mortality in both humans and horses. Infected humans and horses 'produce' insufficient WNV to be taken up by mosquitoes and transmitted onwards.
- A vaccine is available for horses. Uptake of voluntary vaccination is extremely patchy and often happens only at the point when the virus is in circulation.
- No vaccine is available for humans; development has reached an advanced stage, but a vaccine is not yet available/licensed.