West Nile Virus: What is it and how can it affect me?

The West Nile Virus is a seasonal illness transmitted to humans through infected mosquitoes that flares up between May and October. UT Southwestern infectious disease experts Jeffrey Kahn, M.D., Ph.D., and James Luby, M.D., discuss the disease that affects as many as 1,000 people across the country each year.

1. Who is most at risk to contract and become ill from West Nile Virus?
Dr. Luby: Everyone can become infected, but elderly persons and those with a compromised immune system have an extra risk of becoming ill after being bitten by an infected mosquito.

2. Is it more prevalent during certain seasons or in certain areas of the country?
Drs. Kahn and Luby: The virus is most prevalent in late summer into early fall. This year we’re seeing a number of incidences much earlier – possibly because of the warm winter and the normal to slight increase of rain we received this spring.

The virus is not confined to regions with warm climates, but heat is definitely a factor because the incubation period of the virus in mosquitos shortens in hotter conditions. If the Dallas-Fort Worth area’s triple-digit temperatures continue, we’ll likely see more cases. It’s important to note that our area has not had enough overall exposure to this virus to make us immune to its effects – we should continue to take necessary precautions. 

3. How is it spread?
Dr. Luby: West Nile Virus is contracted from a direct mosquito bite. Though it’s a rare event, people can also get it from a blood transfusion.

4. How serious is the virus?
Dr. Kahn: Most people (80 percent) will experience no symptoms at all, about 20 percent will develop a high fever, and less than 1 percent of the population will see neuro-invasive symptoms that affect their central nervous system (brain and spinal cord). In some cases it can be fatal.

5. What are the symptoms? How are they different from the common cold and flu?
Dr. Luby: West Nile Virus symptoms are different from other viral illnesses such as the common cold (i.e. sneezing, runny nose, coughing and a sore throat). The more common symptoms are headaches, high fever, and a stiff neck.  In other cases, the virus is a more serious neuro-invasive disease. Patients may experience a stiff neck, disorientation, unexplained confusion, and in some cases paralysis. Younger patients tend to get the former while older patients tend to experience the neuro-invasive symptoms.

If you begin feeling ill with these more severe symptoms, seek medical attention immediately. Many of these cases do involve hospitalization.

6. What is the incubation period – how long before someone starts to see symptoms after being bitten?
Dr. Kahn: People usually begin feeling the symptoms in two to six days, but it can be as long as 14 days. In individuals with weak immune systems, the incubation period can be up to 21 days.

7. How can I protect myself from getting West Nile Virus? 
Drs. Kahn and Luby: When outdoors use mosquito repellent with DEET, empty standing pools of water around the house, make sure your windows have screens, and avoid excessive outdoor activity during dusk when mosquitos are most active.

8. Is there a vaccine or special treatment for it?
Drs. Kahn and Luby: No, but researchers are working to develop a vaccine. There is currently no specific therapy for West Nile Virus – in most cases medical professionals only are able to treat the symptoms.

For more information, read the Centers for Disease Control's Q&A on West Nile.

Video Resources


Jeffrey S. Kahn, M.D., Ph.D.
James Luby, M.D.

Jeffrey S. Kahn, M.D., Ph.D., Professor of Pediatrics and Microbiology, is Chief of Pediatric Infectious Diseases. His major areas of research interest are viral infections, respiratory infections, and newly emerging viral pathogens.

James Luby, M.D., Professor of Internal Medicine, is the Medical Director for Infection Control at UT Southwestern University Hospitals and Clinics. His major areas of research interest are clinical virology and the epidemiology of infectious diseases, particularly viral infections.