The United States has been hit hard by the largest ever outbreak of West Nile virus, spread mostly by mosquito bites, that has killed 47 people and infected an estimated 95,000 in 38 states.
The number of cases so far this year is the highest recorded through August since the disease was first detected in the United States in 1999, according to the Centres for Disease Control and Prevention (CDC).
"The number of West Nile disease cases in people has risen dramatically. We are in the midst of one of the largest West Nile outbreaks ever seen," Lyle R. Petersen, director of the CDC's division of vector-borne diseases, said at news teleconference Wednesday.
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And it's far from over, noted WebMD, a health website, as right now, the US is in the middle of mosquito season -- and nearly all West Nile virus infections come from mosquito bites. Case counts usually rise through September.
"The number of cases is trending upward in most areas," Petersen was quoted as saying.
He noted 47 states have detected West Nile virus circulating in mosquitoes, birds, or people. Only Alaska, Hawaii, and Vermont have not yet detected the virus.
Petersen said that the reason for the high number of cases this year is unclear, but that unusually warm weather could have fostered favourable conditions for the disease's transfer to humans.
About 75 percent of the cases are in Texas, Mississippi, Louisiana, South Dakota and Oklahoma, CNN reported.
Texas has been at the epicentre of the outbreak, with 586 confirmed cases and 21 deaths, according to the Texas Department of State Health Services.
David L. Lakey, Texas state health commissioner, characterised the situation as a "disaster."
The CDC also is investigating whether the virus might have mutated into a more dangerous form as most West Nile seasons have been relatively mild since 2003, when the virus spread across the US first.
WebMD said the good news is that only one in five people infected with West Nile virus gets West Nile fever. Symptoms appear three days to two weeks after the bite of an infected mosquito.
So far this year, there have been 489 reported cases of West Nile fever. Many cases go unreported.
Illness appears suddenly, said Petersen, who was infected in 2003.u00a0
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