West Nile Virus Facts & History

West Nile is an infection carried by mosquitoes. People get West Nile Virus from the bite of a mosquito that is infected with West Nile Virus. Mosquitoes become infected when they feed on a bird that has the virus in its blood. Once infected the mosquito can spread the virus to humans and other animals.

Anyone can become infected with WNV so it’s important to protect yourself from mosquito bites. People over the age of 50 and those with chronic diseases such as heart disease or cancer may be more at-risk for serious illness. Most human cases occur in the late summer and early fall.

Case History

In Illinois, West Nile virus was first identified in September 2001 when laboratory tests confirmed its presence in two dead crows found in the Chicago area. The following year, the state’s first human cases and deaths from West Nile disease were recorded and all but two of the state’s 102 counties eventually reported a positive human, bird, mosquito or horse. By the end of 2002, Illinois had counted more human cases (884) and 67 than any other state in the United States. In 2003, the epicenter of West Nile disease moved westward. Colorado reported the highest number of cases (2,947), easily surpassing the caseload record for the mosquito-borne disease set the previous year by Illinois. The number of West Nile human cases in Illinois fell dramatically with just 54 reported and only one death. Illinois’ caseload in 2004 was slightly higher than the previous year with 60 reported cases and four deaths. In 2005, Illinois recorded 252 cases and 12 deaths, both totals the second highest in the nation to California’s 880 cases and 19 deaths, and in 2006, there were 215 cases and 10 deaths reported, the sixth highest number of cases in the U.S.

Source: Illinois Department of Public Health

For more information on the History of West Nile Virus, please visit the Illinois Department of Public Health website.

West Nile Virus Symptoms

Serious Symptoms in a Few People

About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include:

  • Coma
  • Convulsions
  • Disorientation
  • Headache
  • High fever
  • Muscle weakness
  • Neck stiffness
  • Numbness
  • Paralysis
  • Stupor
  • Tremors
  • Vision loss

These symptoms may last several weeks, and neurological effects may be permanent.

Milder Symptoms in Some People

Up to 20% of the people who become infected have symptoms such as:

  • Fever
  • Headache and body aches
  • Nausea
  • Sometimes swollen lymph glands or a skin rash on the chest, stomach and back
  • Vomiting

Symptoms can last for as short as a few days, though even healthy people have become sick for several weeks.

No Symptoms in Most People

Approximately 80% of people (about 4 out of 5) who are infected with West Nile Virus will not show any symptoms at all.

Milder West Nile Virus (WNV) illness improves on its own, and people do not necessarily need to seek medical attention for this infection though they may choose to do so. If you develop symptoms of severe WNV illness, such as unusually severe headaches or confusion, seek medical attention immediately. Severe WNV illness usually requires hospitalization. Pregnant women and nursing mothers are encouraged to talk to their doctor if they develop symptoms that could be WNV.

If you suspect West Nile virus symptoms, contact your physician.

Source: Centers for Disease Control