West Nile Virus
Information for Health Professionals

All EEE and WNV disease cases should be reported to the Vermont Department of Health.

History of West Nile Virus in the US

West Nile virus was introduced into the United States in 1999 in New York City. Since then the virus has spread across the country and has caused illness in the 48 contiguous states. Reports of illness peaked in 2003 when almost 10,000 cases were reported nationwide. In 2010, just over 1000 cases were reported.

West Nile virus was first detected in Vermont in 2000, and activity levels peaked in 2002. West Nile virus has been detected in dead birds, mosquitoes, and horses in Vermont. The virus has been found in all counties, but no area of the state appears be at higher risk. It is a relatively uncommon cause of illness in people. Since 2011, two or three infections in people have been reported each year. Prior to that, the most recent documented case of human illness was in 2003. West Nile virus continues to be detected in mosquitoes each year.

The virus is maintained in a bird-mosquito cycle that occasionally spills over into mammals, including humans. Mammals are dead-end hosts and do not contribute to the transmission cycle of the virus.

Return to Top

Symptoms of West Nile Virus

WNV infection is subclinical in 80% about people. Approximately 20% of infections result in West Nile fever which is characterized by non-specific symptoms such as fever, headache and fatigue. Some people will develop a skin rash on the trunk, swollen lymph nodes or eye pain. Recovery is usually complete.

In about 1% of infections, neuroinvasive disease develops, and clinical syndromes ranging from febrile headache to aseptic meningitis to encephalitis may occur. This is most common in older patients. Symptoms may include fever, gastrointestinal symptoms, ataxia and extrapyramidal signs, optic neuritis, seizures, weakness, change in mental status, myelitis, polyradiculitis. A minority of patients with severe disease develop a maculopapular or morbilliform rash involving the neck, trunk, arms, or legs. A few patients develop flaccid paralysis.

Return to Top

Testing and Diagnosis

Arboviral Diseases

All EEE and WNV disease cases should be reported to the Vermont Department of Health.

Return to Top

Contact Us

Department of Health
Tel: 800-640-4374 (Vermont only) or 802-863-7240
Email the Department of Health (general mailbox)

Public Health Laboratory
Tel: 800-660-9997, extension 7560

Epidemiology Field Unit
800-640-4374 (in VT only), or 802-863-7240.

Return to Top