How often does west nile fever turn into west nile encephalitis?

1 in 150: Only 1 in 150 patients infected with the west nile virus develop encephalitis. West nile fever is much more common and is typically a self-limited disease. Individuals more susceptible to developing encephalitis from a west nile infection include the elderly, alcoholics and diabetics.

West Nile Virus: West nile virus travels through an insect vector. The virus will undergoe a viremia state during which it is spread to organs throughout the body, including the brain.

Actually uncommon: Most west nile infections are asymptomatic. Some cause mild flu-like symptoms. Full blown infection of brain is rather uncommon in the normal patient and more often seen with immuno-suppression, such as prior transplants, HIV pts, cancer chemotherapy. The polio-myelitis form is even rarer.