Facebook
Twitter
LinkedIn
Email
 |
Checking for direct PDF access through Ovid | |
Excerpt
West Nile (WN) virus was first isolated and identified in 1937 from an infected person in the West Nile district of Uganda. Since the mid-1990s, the frequency and apparent clinical severity of West Nile virus outbreaks have increased. The flavivirus made its first appearance in North America in New York City in 1999 and continues to expand its endemic areas throughout the United States. An enzootic cycle involving culicine mosquitoes and birds maintains WN virus, with dramatic avian mortality rates accompanying outbreaks in humans in Israel and the US.
The incubation period probably ranges from 3 to 14 days, with onset of illness from July to December, peaking in late August and early September. A febrile illness of sudden onset, often accompanied by malaise, anorexia, nausea, vomiting, eye pain, headache, myalgia, rash and lymphadenopathy, generally lasting 3 to 6 days, occurs in ∼20% of infected persons. One in 150 infections results in meningitis or encephalitis. Risk for severe neurologic disease increases markedly among persons >50 years of age.
Approximately one-half of hospitalized US patients had severe muscle weakness, which may provide a clue to WN viral infection, especially in the setting of encephalopathy. An erythematous macular, papular or morbilliform skin rash involving the neck, trunk, arms or legs is present in a minority of patients.
The most efficient diagnostic method is detection of IgM antibody to WN virus in serum or cerebrospinal fluid. Treatment for WN virus infection is currently supportive, although a clinical trial evaluating the efficacy of alpha-interferon was begun during the 2002 season. Prevention is based on reducing the number of vector mosquitoes and preventing vector mosquitoes from biting humans.
Comment: Case fatality rates among patients hospitalized during recent WN virus outbreaks ranged from 4% in Romania (1996) to 12% in New York (1999) and 14% in Israel (2000). Advanced age is the most important risk factor for death, and patients older than 70 years of age are at particularly high risk.
The origins of WN virus in North America and the clinical spectrum of infection in children are among issues that remain to be clarified. More should be learned about this emerging infection as a result of our 2002 experience, which included the most human cases in the US to date.
