West Nile Virus Infection in Travellers

West Nile virus is a widespread arboviral flavivirus infection occurring nearly everywhere around the globe. It is transmitted by the bite of several mosquitoes, the most epidemiologically relevant of whom belong to the Genus Culex. The natural reservoirs of the infection are several sylvatic birds, where the infection may be mild or life-threatening. Mammals, including humans and equids, are accidentally infected and are considered dead-end hosts, as viraemia does not reach high enough levels to infect biting mosquitoes. In humans, the infection may be asymptomatic (75–80%), mild (essentially febrile syndrome with myalgia, 20–25%) or severe with neurological involvement (1%), with lethal cases especially occurring in immunocompromised and older hosts. Individuals may be infected during travel and the travel medicine doctors must suspect diagnosis promptly among the many viral and bacterial causes of encephalitis and meningitis. Confirmation of West Nile virus (WNV) infection may benefit from molecular tools in the early phase of the infection. Serology is also a useful tool, although cross-reactions may occur. No vaccine nor specific treatment exists so far and prevention of mosquito bites (covering clothes, repellents, mosquito nets) still represents the best preventive measure for the traveller, especially if at risk of severe infection.