West Nile Virus

West Nile Virus

This is an enlarged view of a Culex quinquefasciatus mosquito that had landed upon the skin of a human host, and was about to insert its needle-sharp proboscis through the skin, which would enable it to obtain its blood meal. 

Credit: Credit: CDC

West Nile virus (WNV), a mosquito-borne illness, first emerged in the Western Hemisphere in 1999 in the New York City area and has since spread across the United States. Most people infected with WNV will have no symptoms. About 1 in 5 people infected will develop a fever with other symptoms. Less than 1 percent of those infected will develop a serious, sometimes fatal, neurologic illness.

Why Is the Study of West Nile Virus a Priority for NIAID?

Most human infections are mild, causing fever, headache, and body aches, often accompanied by a skin rash and swollen lymph glands. If the virus crosses the blood-brain barrier, however, it can cause life-threatening conditions that include inflammation of the brain and spinal cord.

How Is NIAID Addressing This Critical Topic?

NIAID supports research on WNV through its comprehensive emerging infectious disease program. This program supports research on bacterial, viral, and other types of disease-causing microbes.

To learn about risk factors for WNV and current prevention and treatment strategies visit the MedlinePlus West Nile virus site.

Biology, Genetics, & Clinical Research

NIAID conducts and funds basic and clinical research on WNV biology and viral structure, ways the virus causes human disease and persists in the body, viral interaction with and transmission among humans, birds, and mosquitoes, processes underlying WNV emergence and ecological patterns in the United States, and insecticide resistance.


NIAID supports research on a variety of vaccine approaches that could potentially lead to a safe and effective preventive vaccine for WNV. These approaches include vaccines containing cocktails of individual WNV proteins and chimeric vaccines, which combine genes from more than one virus into a single vaccine. A third approach involves DNA vaccines, in which DNA that codes for a particular virus protein is combined with bacterial DNA, and the combined product is injected directly into the skin of the person or animal being vaccinated.


Researchers at several institutions are working to develop simple devices for rapid, point-of-care diagnosis of arboviruses (arthropod-borne viruses), including WNV. NIAID-funded scientists are also working to develop rapid diagnostics to detect multiple viruses known to cause hemorrhagic fevers and encephalitis. It is hoped that the different approaches being investigated will lead to cost-effective, rapid diagnostics that could eventually be performed in physician’s offices or even at home, so that treatments could be administered very early in infection to reduce severity of disease.


Through the NIAID Preclinical Services Program, researchers are evaluating compounds for antiviral activity against a panel of viruses, including WNV. In 2011 and 2012, nine compounds were tested for activity against WNV in rodent models of disease, and 220 compounds were tested in vitro (in cell culture). Promising compounds will be further analyzed for safety and efficacy.

Content last reviewed on July 6, 2015