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West Nile Virus - Starting Slow But Picking Up Speed

2006 West Nile Virus Update

The West Nile virus season is off to a slow start this year, but that doesn't necessarily mean we’ll have a worry-free summer and fall, U.S. health officials say. Just because we’re having a late season, that doesn’t mean were going to have an easy season. Mosquito-borne diseases are very difficult to predict.

So far, the virus has been detected in birds, animals or mosquitoes in 28 states. At the same time last year, 48 states plus the District of Columbia reported activity.

Ten people have tested positive for the virus so far this year, one each in California, Colorado, Iowa, Mississippi, Missouri and South Dakota, and two each in Nebraska and Texas. Seven of the cases involved meningitis or encephalitis.

Seven blood donors have also tested positive for the virus -- two in Colorado and one each in Iowa, Kentucky, Oklahoma, South Dakota and Texas. Blood donations are now routinely screened for the virus and if infected, the blood is rejected.

July, August and September are considered peak mosquito-bite months, and health officials expect to see more activity during this period.

Since it's introduction to North America in the New York City area in 1999, West Nile virus has spread across the continent and is now found in every continental state. In 2005 alone, there were 3,000 human cases and 119 deaths linked to infection. This figure is up from 2,539 cases and 100 deaths in 2004, according to the CDC.

West Nile virus is normally passed from an infected mosquito to a bird, and then from the bird to other mosquitoes. The mosquitoes then pass the virus on to humans.

The majority of people who become infected with West Nile virus have no symptoms. Up to 20 percent may experience flu-like symptoms such as fever, headache and body aches or even nausea and vomiting. Only about one in 150 people suffer severe illness, resulting in meningitis or encephalitis. Older people are infected; they are at higher risk for developing severe complications.

While it's not impossible to predict the geographical course of the disease this year, officials say that once a state has reported infections, it's likely they would occur again.

In past years, areas that had unusually hot or dry summers tended to see more activity but there have been exceptions.

Since last year’s storms, people are particularly concerned about the Gulf Coast. The additional debris may give mosquitoes more breeding sites. In Louisiana, more than 40 percent of mosquitoes tested have been identified as positive carriers of the virus.

While human infections have been limited so far, it's never too soon to take precautions.

Health officials recommend removing any standing water where mosquitoes are likely to breed. When out of doors, people should wear insect repellant and long-sleeved clothing.

It just takes one infected mosquito bite to transmit WNV. Even if you aren't noticing a large number of mosquitoes, it's still worth using repellent.

Last year, in addition to the standard DEET-containing products, the CDC also endorsed mosquito-repellents containing oil of lemon eucalyptus and Picaridin. Products containing permethrin can be used on fabrics such as clothes and tents, CDC officials said.

You can find much more information about West Nile Virus in the Medical Articles section of our website.

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