Their role in transmission to humans is uncertain. Spread of West Nile virus between birds and ticks has been demonstrated, providing survival of virus over the winter. West Nile fever virus was first isolated from humans in the West Nile district of Uganda in 1937. Geographically, it occurs in Africa, Europe, SE Asia, Russia, India and Australia. Migrating birds carry the virus over long distances.
Subclinical infection is common.
Meningoencephalitis is the most common complication with cranial nerve palsies, motor weakness, abnormal reflexes and mental status changes. An outbreak in Romania in 1996 led to 400 neurologic cases, primarily in elderly patients. Uncomplicated illness cannot be differentiated from other non-specific febrile illnesses and dengue. West Nile Virus has not occurred in the Western Hemisphere until the recent New York City outbreak in October, 1999. Treatment is supportive.