West Nile Virus
If you think you may have been exposed to West Nile Virus through a mosquito bite, you may wonder what to expect. In the vast majority of cases, you will have absolutely no symptoms at all. When a person does become ill with West Nile infection, health care providers classify their illness one of 2 ways:
West Nile Fever
- Most persons who become infected with West Nile virus (WNV) develop no clinical illness or symptoms. In previous outbreaks in the Northern Hemisphere, an estimated 80% of people who became infected with WNV never developed symptoms attributable to the infection.
- Of the approximately 20% of infected people who do develop symptoms, most develop what has been termed West Nile fever.
- The incubation period for WNV infection is thought to range from about 2 to 14 days, although longer incubation periods have been documented in immunosuppressed persons (people with HIV/AIDS, transplanted organs, and other health issues that make them prone to illness).
- Testing for West Nile Virus earlier than 8 to 14 days after the onset of symptoms may give a false negative result.
Symptoms of West Nile Fever:
- Fever
- Headache
- Fatigue
- Skin rash on the trunk of the body (occasionally)
- Swollen lymph glands (occasionally)
- Eye pain (occasionally)
Severe Disease(Neuroinvasive): West Nile Meningitis, West Nile Encephalitis, and West Nile Poliomyelitis
- About 60% to 75% of people with neuroinvasive WNV infection reportedly have encephalitis or meningoencephalitis, which is noted by a change in mental status and/or severe weakness, paralysis or palsy-like symptoms.
- About 25% to 35% of people with neuroinvasive WNV infection reportedly have meningitis without evidence of encephalitis.
- West Nile meningitis usually involves fever, headache, and stiff neck. Changes in consciousness are not usually seen and are mild when present.
- West Nile encephalitis, the most severe form of neuroinvasive West Nile viral disease, involves fever and headache, but there are more global symptoms. There is usually an alteration of consciousness, which may be mild and result in lethargy but may progress to confusion or coma. Tremors and movement disorders also have been noted.
- West Nile poliomyelitis, a flaccid paralysis syndrome associated with WNV infection, is less common than meningitis or encephalitis. This syndrome is generally characterized by the onset of limb weakness or paralysis. Pain sometimes precedes the paralysis. The paralysis can occur without fever, headache, or other common symptoms associated with WNV infection. Involvement of respiratory muscles can sometimes occur requiring mechanical support (a ventilator) to breathe.
