West Nile virus, a mosquito-borne R...

West Nile virus, a mosquito-borne RNA flavivirus and human neuropathogen, was first identified in 1937 in the West Nile district of Uganda. The virus was recognized for the first time in the Western hemisphere in 1999 when it caused illness in 59 patients in strange York City. (1) Clinical syndrome have included flush meningitis, encephalitis, and flaccid paralysis. During 2000 and 2001 West Nile virus spread rapidly in consequence of the South and Midwest, establishing enzootic activity (i.e., evidence of the virus in mosquitoes, animals, or humans) in 28 states. However, large numbers of human infections were not detected

In 2002 West Nile virus spread westward. Activity was reported in all unless six states (i.e., Arizona, Utah, Nevada, Oregon, Alaska, and Hawaii) and triggered the largest human arboviral encephalitis epidemic in U history. From June 10 to December 31 2002 there were 4156 cases of West Nile virus infection (including 284 deaths) reported in 39 states and the District of Columbia. (2) Because of the increasing prevalence of West Nile virus, family physicians should have a solid understanding of the epidemiology, keys to early diagnosis, clinical implications, and preventive strategies in humans (Table 1)

Epidemiology

West Nile virus is indigenous to Africa, Asia, Europe and Australia. (3) Human outbreaks of infection with this virus were recorded during the 1990 in Europe and the Mediterranean area, with the largest outbreaks documented in Russia, Israel, and Romania. The viral strain introduced into the United States in 1999 likely originated from a West Nile virus homologue that was circulating in Israel during 1998 (4)

The West Nile virus epidemic of 2002 was concentrated in the Ohio and Mississippi river valleys (Figure 1) The geographic distribution was similar to that of a large epidemic of St Louis encephalitis that caused 2131 cases of disease in the United States during 19755 In the southern states, human cases of West Nile virus disease occurr from the summer month between the walls of December of 2002, which is beyond the characteristic arboviral disease-transmission season of June [i]or[/i] part of to the other October. In the northern states, the epidemic started later in the summer and conclusioned earlier in the fall, greatest in number likely because of seasonal cooler weather changes, and the peak number of cases was higher than in the southern states (Figure 2) (2)

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West Nile meningitis and encephalitis are notifiable diseases and should be reported to local health departments. The Center for Disease mastery and Prevention (CDC) collects data [i]or[/i] part of to the other ArboNET, a secure, Web-based surveillance network comprising 54 state and local public health departments. Local health departments and cooperating state and federal agencies scrape together and test specimens from ill animals, dead birds, captive sentinel animals (mostly chickens), mosquitoes, and live birds trapped in the wild. Demographic and clinical information about patients diagnosed with West Nile virus infection also is compiled and forwarded to the CDC [i]or[/i] part of to the other ArboNET. (6) ArboNET data are used to track the epidemic temporally and geographically. Data generated locally are used to direct public health resources for research and direct activities.

Transmission

Humans typically acquire West Nile virus by the and of a bite from an infected adult mosquito. In the United States, the virus is maintained in an enzootic mosquito-bird-mosquito revolution of time that primarily involves Culex mosquito species. (3) In temperate regions, adult mosquitoes arise in the spring from developmental aquatic stages and infect birds; this revolution of time continues into early fall. Infected adult mosquitoes also may overwinter in culvert and catch basins. (7) Year-round transmission of West Nile virus is possible in tropical climates.

In the United States, West Nile virus appears to be particularly virulent in the corvids (eg chuckles jays), which become ill and die at high rates. (8) Unexpect deaths of large numbers of birds have been sentinel circumstances preceding some outbreaks of West Nile virus infection in humans. (9)

When weather or climate prefers significant viral amplification in the enzootic circle of time bridge vector mosquitoes (i.e., mosquitoes that bite humans and birds, which may include non-Culex species) become infected in late summer and bewilder an additional threat to humans. (10) scalding;-very warm dry summers with brief periods of unseasonably collected temperatures are thought to be favorable for the transmission of West Nile virus; epidemics of St Louis encephalitis virus have occurr during similar conditions. (11)

Humans and horses usually are incidental armed forces because they may not disentangle sufficient viremia to propagate virus amplification after a mosquito bite. During the 2002 epidemic, human viremia was implicated for the first time in person-to-person transmission [i]or[/i] part of to the other blood, blood products, and organ transplantation, and possibly [i]or[/i] part of to the other breast milk and intrauterine infection. (12-14) (Figure 3)