Is West Nile Virus Still a Threat?

By Andrea Neblett

Reviewed by QualityHealth's Medical Advisory Board

As wintry weather becomes a faint memory and temperatures start to soar, many of us look forward to spring and summer. We eagerly anticipate outdoor sports, picnics, and days at the beach, and give little thought to pesky mosquitoes and West Nile Virus (WNV).

However, West Nile Virus should definitely be on our radar. Data collected by the U.S. Centers for Disease Control and Prevention (CDC) show that in 2008 there were 1,338 WNV cases reported to the CDC—forty-three were fatal. While these numbers were much lower compared to 2007—3,630 cases and 124 fatalities—there is no doubt that WNV is here to stay.

West Nile Virus was first discovered in Uganda in 1937, but didn’t hit North America until the summer of 1999 when an outbreak occurred in New York City. Since that time over 1000 infected people have died. Thousands more have developed West Nile fever, West Nile encephalitis and West Nile meningitis, and West Nile poliomyelitis.

Encephalitis is inflammation of the brain, or of the brain and surrounding membranes (meningoencephalitis). Meningitis refers to infection and inflammation of the membranes surrounding the brain and spinal cord. West Nile poliomyelitis is inflammation of the spinal cord.

How are Humans Infected?

You can contract WNV if you’re bitten by an infected mosquito that has fed on infected birds. Although the risk is low, the virus can also spread from human to human through blood transfusions, organ transplant, during pregnancy from mother to baby, and possibly through breastfeeding.

Symptoms of West Nile Virus

In most cases there are no symptoms. However, the Mayo Clinic reports that 20 percent of people will develop a mild infection called West Nile fever, which may last a few days or several weeks. Common symptoms are:

Fever
Headache
Body aches
Diarrhea
Vomiting
Loss of appetite
Swollen lymph glands.

Fewer than one percent of infected people will develop West Nile encephalitis or meningitis, or West Nile poliomyelitis. The Mayo Clinic states that the following are common signs and symptoms of these diseases:

High fever
Convulsions
Severe headache
Stiff neck
Disorientation or confusion
Stupor or coma
Tremors or muscle jerking
Signs and symptoms similar to Parkinson's disease
Lack of coordination
Pain
Partial paralysis or sudden weakness
Acute flaccid paralysis, or a sudden weakness in your arms, legs or breathing muscles

Who Is Most at Risk?

If you spend a lot of time outdoors your risk is greatest. Also, elderly people are more likely to develop serious symptoms.

Is West Nile Virus a Threat to Pets?

According to the CDC, cats and dogs can be infected with the virus. So far dogs do not show symptoms when infected, but cats may exhibit mild symptoms, usually a slight fever and lethargy. If you’re worried, there are insect repellents available for cats and dogs.

Horses face a greater risk, with over 14,000 infected and about 4,300 fatalities, reports the National Veterinary Services Laboratories of the U.S. Department of Agriculture. The virus interferes with their central nervous function and causes inflammation in the brain. On a positive note, horses cannot transmit the virus to each other, and there is a WNV vaccine for horses available through veterinarians.

There’s little risk that you’ll be infected by your dog, cat or horse, as there have been no animal-to-human transmissions of WNV (except for mosquito-to-human transmissions).

How to Protect Yourself from WNV

WNV peaks in summer and continues into fall. As the most likely way to be infected is through a mosquito bite, the first rule of prevention is to avoid being bitten.

The CDC recommends spraying on a thin layer of insect repellent, especially those that contain long-lasting active ingredients such as DEET, Picaridin, or, if you prefer more natural repellents, IR3535, or oil of lemon or eucalyptus.

You can use a repellent with DEET on babies over two months old, but use it very sparingly. Or look for a low concentration of this active ingredient. The American Academy of Pediatrics states that a 10 percent concentration will do if you have safety concerns.