TO THE EDITOR: West Nile virus (WNV) is a member of the genus Flavivirus within 
the Japanese encephalitis antigenic complex. The enzootic virus cycle involves 
transmission between avian hosts and ornithophilic mosquitoes, whereas humans 
and horses are considered dead-end hosts. Given the recent increase of WNV 
infection in humans and horses in Europe, concern has been raised regarding 
public and animal health.