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First US Case Of West
Nile Virus In 2004

By Shaoni Bhattacharya
NewScientist.com
5-28-4
 
The first human case of West Nile Virus infection in the US in 2004 has been reported in New Mexico. The mosquito-borne infection, announced on Wednesday, has arrived earlier than 2003's first case, which came at the start of July.
 
"It's the first probable case," says Christine Pearson, a spokeswoman for the US Centers of Disease Control and Prevention (CDC), in Atlanta. "We are working on some confirmatory testing now."
 
The man from San Juan County had only mild symptoms and has since recovered, says the New Mexico health department.
 
"This means West Nile Virus season has started early this year," says Patricia Montoya, secretary of health for New Mexico. "But the virus is one of the few diseases where people can take a few simple precautions, like using a repellent when outdoors, and be protected."
 
The West Nile Virus (WNV) outbreak in 2003 killed 264 people and caused nearly 10,000 cases - more than double the 2002 total. However, many more of the 2003 cases were mild infections, with the number of people seriously affected remaining roughly the same in both years.
 
Active mosquitoes
 
Nick Komar, a research biologist at CDC's arbovirus diseases branch, Fort Collins, Colorado points out WNV can be spread whenever the Culex mosquito species that transmits the virus are active. The virus had already been detected in 2004 in birds and mosquitoes in many southern and eastern states.
 
"In southern California, Culex tarsalis become active in February. In Florida, Culex quinquefasciatus are active all year round. None of the detected WNV activity in the US early in 2004 has been unexpected," he told New Scientist.
 
CDC does not have an official prediction for the 2004 WNV season, but Komar warns: "We must always be prepared for an epidemic. But one human case does not make an outbreak, so it is too early to say what the significance of this case is for the US in 2004."
 
WNV was imported to New York in 1999, from where it spread across the country. In the last two outbreaks, the disease hit the western states harder.
 
"WNV has arrived in the western US relatively recently, and will probably continue to spread there," says Komar. "As it does, more people will be at risk, so it is possible that there will be more western US cases in 2004 than in previous years."
 
Herd immunity
 
As part of its WNV research, CDC is studying the immunity of house sparrows. These birds are not harmed by WNV but are an important host for the virus, which is passed from infected birds to humans and horses via mosquitoes.
 
The virus is already endemic in some areas and when this happens, birds develop immunity. If enough become immune - "herd immunity" - the virus would die out, and transmission to humans might stop.
 
Komar, who is running the study in Colorado, says that a preliminary survey of house sparrows this spring in 23 towns has found a "spectrum of immunity" ranging from seven to 54 per cent. This means they are not close to the herd immunity level yet.
 
"It seems clear that the majority of sparrows will be susceptible to infection and therefore available to contribute to the transmission cycle in 2004," he says. However, it is likely that herd immunity will develop eventually, as has happened in Africa where WNV has been endemic for many years.
 
© Copyright Reed Business Information Ltd. http://www.newscientist.com/news/news.jsp?id=ns99995053


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