West Nile Virus: What You Should Know
What’s In This Guide

For most people, the arrival of warm spring and summer weather ushers in pleasant thoughts of sunny days spent relaxing outdoors with friends and family, maybe at a beach or park or just hanging around at a backyard barbecue or pool party.
After a winter’s worth of bleak, gray, cold weather, few things replenish the spirit like a little rest and relaxation in the great outdoors. But as idyllic as all that sounds, there’s a very real danger lurking outside, and it comes from tiny uninvited guests – mosquitoes carrying the highly contagious West Nile virus (WNV).
Every year, about 2,000 cases of West Nile Virus are reported to the Centers for Disease Control and Prevention (CDC), but thousands more may become infected with the disease and not even know it. Up to 80% of those infected with WNV won’t develop any symptoms or will develop symptoms so subtle and relatively brief that the infection may go undiagnosed. In the other 20%, the infection can cause more pronounced symptoms, with a few developing severe and even life-threatening side effects.
Although the chances of developing these more serious side effects is slim, knowing what to look for can help ensure you seek medical attention at the first sign of symptoms, in addition to taking steps to prevent the illness in the first place.
What is West Nile Virus?

WNV was first isolated in a Ugandan patient in 1937. By the 1990s, outbreaks had been reported in Europe. In 1999, an outbreak in New York City marked the first known invasion of the virus in the Western hemisphere. Since then, the disease has spread throughout the U.S. and Canada, as well as Central and South America.
How Does West Nile Virus Spread?

What are the Symptoms of West Nile Virus Infection?

Anyone can become infected with West Nile virus, but serious side effects are most common among people over 60 years of age and those with compromised immune systems, as well as people with chronic illnesses like high blood pressure, cancer, kidney disease and diabetes, and those who have had organ transplants.
West Nile Virus FAQ and Statistics
Since 1999, about 44,000 cases of West Nile virus infection have been reported to the CDC; about half of those have been the more severe form of the disease that attacks the central nervous system.
In most people, it takes from two days to about a week from the time of the mosquito bite to the onset of symptoms.
Most infections occur between June and September.
The virus is diagnosed through blood tests or by analyzing the patient’s spinal fluid to look for antibodies produced in response to the infection.
Because birds are a primary host for West Nile virus, the CDC recommends reporting dead birds to your local or state health department to enable them to perform testing or other reconnaissance efforts in your area.
West Nile virus is only spread by the female mosquito, which needs blood to produce her offspring. Male mosquitoes do not bite.
WNV can infect any mammal. In fact, researchers in Texas discovered that a male killer whale housed in a San Antonio marine park died of West Nile virus in 2007.
Anyone can become infected with West Nile virus, but serious side effects are most common among people over 60 years of age and those with compromised immune systems, as well as people with chronic illnesses like high blood pressure, cancer, kidney disease and diabetes, and those who have had organ transplants.
How to Prevent West Nile Virus Infection
- Avoid being outdoors when mosquito activity is at its peak, typically between dusk and dawn.
- Stay away from standing water or other damp areas likely to host breeding populations of mosquitoes.
- Cover beds with mosquito netting if you sleep outdoors or in areas with unscreened windows or doors.
- Wear long pants and tops with long sleeves.
- Purchase clothing and gear that’s been pretreated with repellent, or apply repellent to your clothing and outdoor gear yourself.
- Use mosquito repellent products approved and registered by the Environmental Protection Agency (EPA), and always follow application instructions carefully.
Take care with personal mosquito repellents:
Using them on young children can cause serious side effects, including poisoning. In general, insect repellents should never be used on infants under two months old, and products containing oil of lemon eucalyptus or para-menthane-3,8-diol should not be used on children under three years. Before using any repellent, ask your pediatrician to recommend products safe for children, as well as tips on proper application. Use mosquito netting over cribs and strollers.

If you still have mosquito issues after trying all these methods, wide-scale repellent products and insecticides can help keep the mosquito population under control. Use extreme caution with commercial products – they can cause serious and even deadly side effects to wildlife, as well as pets and humans. Calling in a pest control company with extensive experience in mosquito control can be a wise investment to ensure that these products are applied properly.
West Nile Virus in Horses, Pets and Other Animals
Horses are more vulnerable to the West Nile Virus. They tend to be much more susceptible to infection and much more likely to develop serious side effects, including death. Statistics from the New Jersey Agricultural Experiment Station of Rutgers University report equine mortality rates of about 34%, with data from Pennsylvania reflecting about a 40% mortality rate from the disease.
In horses, symptoms of West Nile infection are often similar to other types of encephalitis and can include:
- loss of appetite
- weakness or paralysis of hind limbs
- vision problems
- difficulty swallowing
- head pressing
- walking in circles or aimless wandering
- depression
- hyperexcitability
- seizures
As with humans, this virus cannot be spread from one mammal to another. It can only be transmitted by a mosquito that becomes infected from biting a host bird. West Nile Virus is just one of several serious diseases that can be transmitted by mosquitoes.
Although the incidence of serious mosquito-borne infection may be relatively rare, it only takes one infected mosquito to cause a life-threatening disease. Taking precautions to prevent infection should become part of your normal spring and summer routine. Get family members involved, and work as a group to identify and eliminate risks, including containers or areas of standing water and damaged window or door screens or seals, and look into pest control options early in the season. Mosquito control is one activity where devoting a little time to prevention can yield major benefits for you and for the ones you love.

If you still have mosquito issues after trying all these methods, wide-scale repellent products and insecticides can help keep the mosquito population under control. Use extreme caution with commercial products – they can cause serious and even deadly side effects to wildlife, as well as pets and humans. Calling in a pest control company with extensive experience in mosquito control can be a wise investment to ensure that these products are applied properly.

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