A primer on West Nile Virus

Culex mosquitos (Culex quinquefasciatus shown)...
Culex mosquitos (Culex quinquefasciatus shown) are biological vectors that transmit West Nile Virus. (Photo credit: Wikipedia)

Lately there has been a lot of coverage about West Nile virus in the news. In fact, for a variety of different factors this is shaping up to potentially be the worst outbreak since the disease peaked in the US in 2003.

Right now in early September we are in the mid-season of West Nile activity and new cases will continue to be reported in the coming weeks. While this is an important disease to be aware of there are some very basic steps that can be taken to protect you from infection. Widespread panic is completely unnecessary as preventative measures are effective despite the lack of approved treatments for this disease.

Keep reading for an overview of the diseases caused by West Nile virus, where it is, and how to disrupt transmission of the virus to prevent infection.

Where is West Nile?

Map of West Nile Virus activity
Img courtesy of CDC: http://www.cdc.gov/ncidod/dvbid/westnile/Mapsactivity/surv&control03Maps.htm

In 1999 there was an unexplained outbreak of disease among birds in city zoos which were later linked to fever cases throughout parts of the city. It was discovered that these were linked by the West Nile virus, a member of the flavivirus family related to Japanese encephalitis virus. Since its introduction in 1999 West Nile virus has spread to all of the lower 48 states. Shown above is the West Nile activity in 2003, current peak year for human West Nile infections.


How do I get West Nile?

This virus is transmitted by the bite of the Culex and Aedes mosquitoes. It cannot be transmitted person-to-person so being near ill-persons is not dangerous as long as no mosquito vectors are present.


What are the symptoms?

Roughly 20% of those infected with West Nile virus will develop the disease West Nile fever, or 1 in 5 people.  Symptoms of West Nile fever include fever, headache, fatigue, and occasionally include eye pain, swollen lymph nodes, and a rash on the skin covering the trunk of the body.*

In addition to fever, West Nile virus is also capable of infecting the brain in roughly 1 out of every 150 people infected, or 0.67%. This can result in encephalitis; a dangerous swelling of the brain which can be fatal. This may also manifest as meningitis; an inflammation of the meninges that encases the brain. For reasons yet to be understood those over the age of 50 and immune compromised patients such as transplant recipients are at the highest risk of developing this disease after infection.

It is important to remember that while this disease does have significant clinical manifestations the actual disease burden in infected individuals is lower, 80% of persons will not experience symptoms.


What are the treatments?

Currently there is no vaccine for West Nile and no specific therapies for West Nile virus encephalitis, which is the major cause of death for those infected. Clinical therapy is currently limited to supportive care making the search for novel therapeutics for this disease of high importance.


How can we prevent it?

There are no available vaccines for West Nile virus as of today. However, by reducing contact with the mosquito vectors is highly effective in preventing the contraction of this disease. Standard mosquito control strategies are effective, such as:

  • draining all standing water from around your home so that mosquitoes do not breed (tires, empty garden pots, etc.)
  • using insect repellents
  • avoiding the outdoors at dawn and dusk when the mosquitoes are most active
  • securely screening all windows and doors on your home
  • wearing long-sleeved clothing, socks, and pants to keep mosquitoes from feeding upon you



While West Nile virus is capable of causing significant clinical disease but it is not so prevalent that we must fear it. With some basic preventative measures we can help contain the spread of this disease in human populations until more effective therapies and vaccines are available.


* http://www.cdc.gov/ncidod/dvbid/westnile/clinicians/clindesc.htm