West Nile Virus

Introduction

Culex mosquito on skin and bucket of standing water

West Nile virus is spread by mosquitoes, which breed in standing water.

West Nile is a mosquito-borne virus that can cause serious neurological disease in humans and animals, including encephalitis, a potentially fatal inflammation of the brain, and meningitis, inflammation of the tissues that cover the brain and spinal cord. Commonly found in Africa, West and Central Asia, and the Middle East, the virus was first detected in the United States in 1999.

Since its North American appearance in New York, the virus has spread across the United States and northward into Canada and southward into Mexico, Central America, and the Caribbean. In 2002, a total of 4,156 people become ill from the virus in the United States; 284 died. This outbreak was the largest mosquito-borne encephalitis epidemic ever documented in the Western Hemisphere.

It is unclear how serious the disease will be in the future, but if past experience is any guide, the majority of cases will appear in late summer.

Although West Nile virus infections can be serious, the impact of the virus should be kept in perspective. While hundreds of thousands have been affected by this emerging infectious disease, millions of people in the United States get the flu each year, and the U.S. Centers for Disease Control and Prevention estimates that on average 36,000 Americans die from influenza-related complications yearly.

So why does a disease such as West Nile that affects relatively few people have so many people worried?

For most Americans, the prospect of a deadly disease borne by mosquitoes is new. Unlike people in other parts of the world who contend with endemic mosquito-borne illnesses such as malaria, dengue fever, or other forms of encephalitis, Americans have tended to think of mosquitoes as a mere annoyance. The attitude probably arose because cases of other forms of mosquito-borne diseases have been sporadic in this country for the past 40 years.

However, the introduction and rapid spread of West Nile virus in the United States should be considered a warning that in today's era of modern transportation, other, perhaps more deadly, mosquito-borne exotic viruses may be introduced.

While we may feel helpless in the face of this new health threat from mosquitoes, the risk is relatively small. There are steps that we can take to protect ourselves, our families, our communities, and our pets and livestock.

Understanding more about West Nile can help us reduce our risks from this and other mosquito-borne illnesses.

What It is and How It's Transmitted looks at the virus and how it spreads.

Prevention shows what you can do to protect yourself, your family, and community from West Nile virus.

Humans and West Nile looks at the risk of infection and how to recognize signs and symptoms of disease.

Animals and West Nile explores risks to animals and how to protect them from infection.

Research and Surveillance explains what scientists are doing to minimze the risk of West Nile and control its spread.

Oct. 8, 2003