Title : Mosquito-borne virus has become widespread
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Mosquito-borne virus has become widespread
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The name conjures up images of African deserts and rain forests, but the West Nile virus has quickly made at home in the United States.
Since the first cases in the United States appeared in New York in 1999, the virus has spread from coast to coast, and health experts public agree that this mosquito-borne infection will not disappear.
"is here to stay," says Richard Pollack, Ph.D., an instructor of tropical public health at the School of Public Health at Harvard.
The number of reported human cases peaked at 9,862 in 2003, including 264 deaths, according to figures from the US Centers for Disease Control and Prevention (CDC). In late 2004, cases had appeared throughout the continental United States except Washington. However, the total number of cases was significantly reduced to 2,535, with 98 deaths.
Mild and severe
"West Nile virus is responsible for many human and disease deaths each year. Most people who contract West Nile virus without But do not get sick, and most of those who become ill do not become deeply sick, "says Pollack.
The CDC estimates that less than 1 percent of people infected with West Nile virus become severely ill. These cases can include swelling of the brain or tissues that cover (encephalitis or meningitis). Some of the most severe cases may also result in a type of muscular paralysis that resembles polio.
According to the CDC, about 20 percent of those infected will develop West Nile fever, a flu-like illness. Symptoms of West Nile fever include fever, headache, fatigue, muscle pain, eye pain, rash, nausea and vomiting. West Nile fever can be debilitating, causing those affected to miss school or work.
Most Americans who are infected with West Nile virus experience no symptoms. Many people probably will never know they were infected.
"However, because of the small chance of serious illness, is still very important to take precautions against infection by the West Nile virus," says Jennifer Brown, DVM, MPH, a veterinarian in the Epidemic Intelligence service of CDC.
In 2004, 44 percent of reported cases in the United States were the cases of severe illness affecting the central nervous system. Fifty-five percent were cases of West Nile fever.
Brown says there are probably many more cases of West Nile fever in 2004 but were undiagnosed or unreported.
How virus Western
Nile spreadsWest Nile is transmitted through the saliva of mosquitoes. In this country, the main culprits are the Culex mosquitoes, although other types of mosquitoes can also be involved. Culex mosquitoes favor standing water in gutters choked lack of leaves, storm drains and pools obsolete, says Pollack. Other types of mosquitoes prefer the edges of shallow ponds, wetlands, floodplains flooded, or even tree holes filled with water or cans.
Only the female mosquito feeds on blood. Culex mosquitoes tend to prefer the blood of birds, but are not always as demanding, says Pollack.
"If given the option, they will probably go after a bird. Most of the West Nile virus bounces between birds and Culex mosquitoes. But if they're hungry and you're on the road some of these mosquitoes also feed on people, dogs, raccoons, almost any vertebrate animal. "
once inside a suitable bird, the virus can multiply" to an incredible degree, "says Pollack . "Some birds succumb to infection and die, but others tolerate it very well and can then infect many more mosquitoes. It is likely that many tens of thousands of birds die each year in the US, due to this virus. Crows are particularly susceptible and this virus is said to have devastated populations crow in many areas. "
in addition to transmitting mosquitoes, in 2002 nearly two dozen people became ill from West Nile virus transmitted by blood transfusion . In 2003, blood banks began testing for the virus to reduce the risk of transfusion-related infections.
How did you get here?
The West Nile outbreak in the United States began in the late summer of 1999 in New York City.
Originally, CDC officials thought it was St. Louis encephalitis, another mosquito-borne virus - until they realized that the birds were also dying. St. Louis virus usually does not kill the birds. Tests revealed that the culprit was something unexpected -. West Nile Virus
How did this virus, known in Africa, Europe, the Middle East and parts of Asia, reaching the United States?
Researchers do not really know. "We have a strong indication of where it is in reality," says Pollack. "The strain was isolated in New York was virtually identical to a strain that was isolated from the previous year in Israel, but less closely related to isolates from outbreaks in other countries."
Pollack says the virus could have been brought by a person who was not aware of being infected, a migratory bird blown off course by a storm, or a bird (or other animal) smuggled into the country .
His favorite theory is that an animal infected with West Nile hitchhike inside an airplane mosquito.
future cycles
Future outbreaks in any particular area are likely to occur in cycles, says Pollack.
"When West Nile reaches a new region that has a huge population of what we call naive hosts - birds that have never seen before and are susceptible to this infection," he says. "So you can infect lots of birds." Birds infect more mosquitoes, which in turn can spread the virus to people and other animals.
"However, survivors are then essentially immune, and will moderate the spread of infection in the future," says Pollack. Once the immune birds in an area grow old and die, and are replaced by other birds who are not immune, another local outbreak becomes more likely, he says.
Prevention
public health officials around the country have occupied West Nile, in part, by controlling populations of birds and mosquitoes. They test a proportion of dead birds found in an area to detect the virus, and can also sample and test mosquitoes.
The authorities are also making greater efforts to eliminate standing water or treat areas that can breed mosquitoes. These can include anything from storm drains and ponds backyard breeding ground such as open garbage bins and birdbaths.
In many areas, officials have used insecticides to kill mosquito larvae. If there has been an outbreak sometimes they have spray to kill adult mosquitoes.
For tips on what you can do at home to protect themselves from mosquito-borne diseases, read our tips on staying safe.
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