West Nile Virus: A Summertime Threat

One doctor answers common questions about a dangerous summertime infection.

ByAbbigail Chandler, M.d.
February 10, 2009, 3:07 PM

July 3, 2007— -- With summer now in full swing, the kids are out of school and off on camping trips, beach excursions, picnics, bicycle rides and outdoor sporting events.

Most of us are familiar with the summertime dangers of sun exposure and recreational injuries, but few may know the true hazards of mosquito bites.

The vast majority of these bites cause a harmless, annoying itch that resolves in a few days. However, some mosquito bites could infect you with West Nile Virus -- a microorganism that could cause you or your child to develop fever, headache, body aches — or worse.

Do you know how to protect yourself?

West Nile Virus is a disease that spreads from the bite of infected mosquitoes to birds and humans. Horses, cats, dogs, rabbits, squirrels, bats and skunks can also be infected, albeit less often.

West Nile Virus was first discovered in 1937 in a feverish woman in Uganda, Africa. Over the decades it has slowly spread across the globe, and it made its U.S. debut in New York City in 1999.

Prior to this time, the infection was unknown in the United States; now, however, it has become common throughout the country, having been reported in all 48 mainland states and the District of Columbia.

Last year the virus was particularly active; although only 4,261 cases were officially reported, the Centers for Disease Control and Prevention (CDC) estimates that more than 43,000 West Nile infections occurred in the United States during 2006.

West Nile Virus can cause three different illnesses in humans. The first type, asymptomatic West Nile, occurs in 80 percent of people bitten by an infected mosquito and causes no symptoms at all and resolves on its own.

The second type of illness is called West Nile Fever. About 20 percent of people infected with the virus have this disease, which includes high fever, headache, body aches, nausea, vomiting and a rash on the abdomen and back. Symptoms start three to15 days after a mosquito bite and may last a few days to a few weeks.

The third and most serious type is called Neuroinvasive West Nile, which can cause encephalitis or meningitis. In this disease, the virus invades the nervous system (brain and spinal cord).

Fortunately, less than one percent of people -- about one in 150 -- who come into contact with West Nile will develop this problem. Patients can have high fever, headache, neck stiffness, confusion, tremors, seizures, weakness, changes in their vision, and even coma. These symptoms may last for weeks and may even be permanent.

People over age 50 are at a higher risk for developing Neuroinvasive West Nile, but even young healthy people can become very sick from West Nile Virus.

If a person has symptoms of West Nile virus, their physician will perform blood tests and/or a spinal tap to look for the virus. A spinal tap is done using a very small needle inserted into the lower back to remove fluid from around the spinal cord.

Many other viruses and bacteria that cause meningitis or encephalitis cause similar symptoms to West Nile infection, so these tests are necessary to determine which infection a person has. A CT scan of the brain does not provide much help because it is usually normal, but an MRI of the brain may be useful.

Unfortunately, there are no good medicines to treat West Nile Virus. Most mild symptoms pass on their own, and patients recover completely.

In severe cases, patients may need to be admitted to the hospital to receive "supportive care," which includes treatment such as infusing fluids into a person's veins, supplemental nutrition or even the help of a breathing machine.

The good news is that people can take steps to protect themselves against West Nile.

If you have the symptoms described above, call your physician and make him or her aware of you concerns.

If your symptoms are severe or you are having difficulty breathing or walking, or if you have confusion, you should call 911 or go to the nearest Emergency Department immediately.

For more information, visit www.cdc.gov/westnile.

Dr. Abbigail Chandler is an infectious Disease physician with the Infectious Disease Associates of Tampa Bay.

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