Indicator Profile of West Nile Virus Infections
Why Is This Important?
WNV is spread to humans primarily through the bite of infected mosquitoes. Mosquitoes become infected when they feed on infected birds that have high levels of WNV in their blood. WNV affects all age groups in humans and can potentially become a serious illness. The virus was found in the U.S. in 1999 and in Utah in August 2003. WNV is commonly found in Africa, West Asia, and the Middle East. The virus has now spread throughout most of the U.S., Canada, Latin America, and the Caribbean islands.The most frequent signs of WNV illness usually begin 3-15 days after a bite from an infected mosquito. Symptoms can last a few days, several weeks, or become permanent.
Most people infected with WNV do not develop symptoms, however, it is possible that some people may have mild symptoms or serious symptoms. Approximately 80% of people infected with WNV do not develop symptoms of the disease. About 20% of people infected with WNV will develop mild symptoms, or West Nile fever. Symptoms of West Nile fever may include fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach, and back. Symptoms can last for as short as a few days, although even healthy people have become sick for several weeks. Serious symptoms, or neuroinvasive disease, are rare and affect the nervous system. Only about 1 person per 150 people infected with WNV develops this type of illness. Neuroinvasive disease can include either West Nile encephalitis (inflammation of the brain) or West Nile meningitis (inflammation of the membranes of the brain or spinal cord). Symptoms of neuroinvasive disease may include high fever, headache, neck stiffness, stupor (minimized reactivity to the surrounding environment), disorientation (loss of familiarity with one's surroundings), coma (an unconscious state from which one cannot be awakened), tremors (repetitive, irregular contractions of muscle groups), convulsions (violent spasms or series of jerking of the face, trunk, or extremities), muscle weakness, vision loss, numbness, and paralysis (incapable of movement). Symptoms may last several weeks, and neurological effects may be permanent. People over the age of 50 years are at the highest risk of developing serious symptoms. There is no way to predict if someone will develop illness or not after being bitten by an infected mosquito.
Number of Human and Animal West Nile Virus Infections Reported by Year, Utah, 2003-2007
Data Notes
In 2003 the Utah Department of Health received one case of human West Nile virus infection. Animal in the above graph includes horses that tested positive, dead birds that tested positive, sentinel chickens that tested positive based on weekly surveillance blood testing, and mosquito pools that are routinely collected, speciated, and tested for West Nile virus that tested positive.Data Sources
Utah Department of Health, Bureau of Epidemiology;Definition
West Nile virus (WNV) is a virus that causes flu-like and neurological (of the nervous system that includes the brain, spinal cord, and nerves) illness in humans, birds, mosquitoes, and some non-human mammals.How We Calculated the Rates
| Numerator: | Number of human and/or animal West Nile virus infections reported to the Bureau of Epidemiology. Animal includes horses that tested positive, dead birds that tested positive, sentinel chickens that tested positive from routine weekly blood draws, and mosquito pools that tested postive. Mosquito pools are routinely collected, speciated, and tested for West Nile virus during the season. |
| Denominator: | Not applicable. |
Page Content Updated On 06/11/08,
Published on 06/13/08
