08/03/2012 05:06 pm ET Updated Oct 03, 2012

West Nile: What You Should Know

The New York Department of Health and Mental Hygiene (DOHMH) reported Monday that the city's first West Nile viral infection of 2012 has been confirmed in a Staten Island man. According to the United States Centers for Disease Control and Prevention (CDC), he remains the only human case in New York state. However, as of July 31, 241 individuals in 22 other states are reported to be infected, 145 of those in Texas.

The disease is most commonly spread by mosquito bite and has been discovered in mosquitoes in every borough of New York City other than Manhattan. Since July 1, the DOHMH has has identified 99 mosquito breeding pools positive for West Nile virus in New York City, 72 of those in Staten Island, 24 in Queens, two in Brooklyn, and one in the Bronx. While the first case occurring in Staten Island isn't a surprise, given that the majority of viral activity is there, residents of other boroughs are still at risk, particularly those over the age of 50.

It is estimated 80 percent of those infected with West Nile virus don't experience any symptoms of the illness, which resolves without medical attention. The majority of those that do experience symptoms of the illness develop what is commonly called "West Nile fever." This is typically characterized by fever, headache, fatigue, and occasionally with swollen lymph glands and a rash on the skin of the chest, back, and abdomen.

If the disease progresses and affects the central nervous system, it can lead to meningitis, an irritation and inflammation of the tissue that surrounds and protects the central nervous system in the brain and spinal cord. This is characterized by a sudden high fever, severe headache, a stiff neck, and may include seizures, tremors, or "stupor," a dazed state of disorientation.

West Nile viral infections may also progress to encephalitis, which is an infection of the brain itself. While mild cases show flu-like symptoms, such as a fever, chills, headache, fatigue, and nausea, more severe cases can result in "problems with speech or hearing, double vision, hallucinations, personality changes, loss of consciousness, loss of sensation in some parts of the body, muscle weakness, partial paralysis in the arms and legs, sudden severe dementia, impaired judgment, seizures, and memory loss," according to the National Institutes of Health.

Both of these conditioins are potentially life-threatening and should be treated promptly. To diagnose these conditions, health care providers will likely conduct several blood tests. These will check for the presence of an increased white blood cell (WBC) count, antibodies specific to West Nile virus, and levels of other cells and minerals. They may also conduct a computed tomography or "CT" scan in order to exclude any other causes of the symptoms. If these findings are consistent with West Nile encephalitis or meningitis, a sample of cerebrospinal fluid (CSF) may be taken from a lumber puncture after the lower back is made numb to confirm the diagnosis.

West Nile virus has the highest rates of both meningitis and encephalitis in the elderly, so both the CDC and New York's DOHMH recommend that this group take extra precautions. To avoid being bitten by mosquitoes, they recommend wearing protective clothing, such as long-sleeved shirts and long pants, particularly when outdoors at dawn or dusk, when mosquitoes are most active. They further recommend avoiding shaded, brushy areas, applying to any exposed skin a repellent containing DEET, picaridin, oil of lemon eucalyptus, of IR3535.

Finally, they recommend removing any nearby standing water that can serve as a breeding pool for mosquitoes, such as in old tires, ceramic pots, wheelbarrows, plastic bottles, and so on, as well as changing the water in bird baths every three to four days.

Numbers of infections in the U.S. has come down considerably, from a relative peak at 9,862 in 2003 to only 712 in 2011. With less than 1 percent developing encephalitis, this leaves New Yorkers fairly safe. However, 10 to 15 percent of those cases of encephalitis are fatal, so those experiencing the symptoms of severe illness listed above shouldn't hesitate to seek care.

For more information on West Nile virus, please check the New York City Department of Health and Mental Hygiene website, the Centers for Disease Control and Prevention website, or contact your health care provider.

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