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West Nile virus infection is a mosquito-borne disease that is usually mild and often gets better without treatment. However, a few people suffer from severe complications, which can lead to costly hospitalization and loss of work.

U.S. Centers for Disease Control and Prevention (CDC) reports that the country spends millions of dollars each year in the treatment of West Nile virus disease, a condition transmitted to humans by a mosquito bite. In fact, hospitalizations and follow-ups related to the disease cost nearly $800M in healthcare expenses as well as lost productivity since 1999. This means that the United States spends about $56M annually for direct and indirect costs brought about by the mosquito-borne West Nile virus. These findings were based on research published online by the American Society of Tropical Medicine and Hygiene.


The Cost of West Nile Virus Disease

Recent research shows that being bitten by a mosquito that transmits the West Nile virus (WNV) can cost the government millions of dollars in terms of hospitalization, medications, follow-up visits, and lost work. After examining more than 37,000 WNV infections reported to the CDC (1999-2012), investigators found more than 18,000 patients were hospitalized and more than 1,500 people died from the disease. More than 16,000 individuals developed complications, such as neurologic sequelae, of which elderly patients were at high risk for severe complications. However, CDC reports that the number of patients affected by the disease may be more than the actual cases reported since 1999. Furthermore, the researchers believe that the costs calculated may have been underestimated since most of these were based on initial costs incurred and may have not included additional costs involved in the burden of the illness.

Indirect costs for lost work and reduced productivity due to the illness are significant especially for younger patients who suffered from neurological complications such as meningitis.

On the other hand, older patients were more likely to suffer from encephalitis, also affecting the brain, although most of them have retired from work.

The findings are useful but the authors believe that a more accurate estimation of costs related to direct and indirect effects of the disease will determine if spending on developing new vaccines, drugs and mosquito control measures is cost-effective.

What is the West Nile Virus?

In 1937, a mosquito-borne virus was identified in the West Nile district in Uganda. It was first recognized in 1999 in the USA, where it caused 59 New York City residents to suffer various clinical syndromes characterized by fever, encephalitis, meningitis, and paralysis. In the two years that followed, the virus rapidly spread westward, affecting 28 states. Since then, more than 30,000 patients have been affected and more than 1,200 people have died.

According to epidemiologists, WNV causes a seasonal epidemic that usually begins in summer and may continue until the fall season. 

The virus is transmitted from infected birds (usually jays and crows) to humans only through bites from certain adult mosquitoes that bite both birds and humans.

The virus is not spread through person to person contact, animal to person contact nor by eating dead animals. However, it is possible (though rare) to transmit the virus through blood transfusion, organ transplant, child birth or laboratory exposure.

Signs And Symptoms Of West Nile Virus Infection

Almost 80% of patients infected with WNV do not manifest any symptoms.


Only one in five people will have a mild illness after an incubation period of 2-15 days. These patients may have:

  • fever, chills

  • body aches and pains

  • headaches

  • tiredness

  • non-itchy rashes on the arms, chest, and back

  • loss of appetite

  • nausea and vomiting

  • swollen lymph glands

These non-specific symptoms may last for less than a week and patients may get better without treatment, not even being aware that they have the virus. However, one out of 150 infected people will experience neurologic symptoms such as:

  • neck stiffness

  • muscle weakness

  • disorientation

  • tremors

  • convulsions

  • loss of vision

  • numbness

  • paralysis

  • stupor

  • coma

These symptoms may be manifestations of encephalitis, meningitis, or poliomyelitis-like syndrome, which may last for several weeks. Neurological deficits may become permanent and death may occur.

Most patients with mild febrile illnessmay not be suspected to have WNV and may be treated for other viral illnesses.

However, in patients who have unexplained neurologic manifestations during the mosquito season (late spring to fall), physicians should consider WNV infection.

Diagnosis of WNV disease may be established based on a four-point criteria set by CDC, which tests for antibodies specific to WNV as well as antibodies for other infections that cross-react with WNV.

Treatment of West Nile Virus Infection

Most people who are infected with the virus will get better on their own, without any treatment. Some may take acetaminophen for fever and headaches and others may treat their symptoms like any viral disease (bed rest, increased fluid intake). However, symptoms may last for weeks or months.

There is no specific treatment, antidote or vaccine for this viral infection.

Intensive treatment and hospitalization may be required for severe illness with neurologic complications. Treatment consists of supportive measures including intravenous fluid administration, intensive medical monitoring, ventilator therapy for breathing problems, anti-inflammatory medications, and prevention of secondary infections such as pneumonia.

Studies are still being done to look into the usefulness of interferon treatment for WNV infection.

How to Prevent West Nile Virus Infection

The best way to prevent WNV infection is to avoid being bitten by mosquitoes.

Mosquito control methods include eliminating mosquito breeding places such as flower posts, barrels, buckets, bird baths, pet dishes, kiddie pools or any container that holds water. Keep mosquitoes out of your house by installing screen on windows and doors if necessary. Protect yourself from mosquito bites by:

  • Staying indoors when mosquitoes are active.

  • Using mosquito repellents with DEET, IR3535, picaridin, eucalyptus oil or para-menthane-diol.

  • Not wearing perfumes, lotions or other scented body care products, which can attract mosquitoes.

When to See a Doctor

During the mosquito season, one must take care to observe if fever, headache and body aches last for two or three days, because these may be symptoms of WNV infection. Call your doctor if you suspect you may be experiencing symptoms of neurologic disease such as meningitis or encephalitis. Pregnant women must consult their doctors immediately if symptoms persist, since the virus may be passed on to their babies.

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