Health Alert

Arboviral Disease Advisory

Eastern Equine Encephalitis and West Nile Virus Season in Vermont

To:      Vermont Healthcare Providers and Clinical Laboratories
From:  Patsy Kelso, PhD, State Epidemiologist for Infectious Disease
Date:   June107, 2011

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When to consider arboviral disease in your differential diagnosis
We don’t yet know if the heavy spring rainfall will mean an increase in arboviral activity in Vermont. Nevertheless, in patients with acute febrile illnesses, especially those with aseptic meningitis or encephalitis, it is important to consider EEE and West Nile virus as part of the differential diagnosis.

Eastern Equine Encephalitis
Eastern Equine Encephalitis (EEE) has never been diagnosed in a person or animal in Vermont, but in the fall of 2010, we found evidence that EEE virus is present in Vermont. Results of a novel surveillance project found antibodies against EEE virus in both deer and moose blood samples collected from harvested animals during rifle season. Positive samples were found in animals from many different parts of the state. Since deer have a limited home range, it is likely the animals were exposed close to where they were shot. It is not surprising that there is EEE virus in Vermont since the virus has caused human and animal illness in our bordering states and Quebec.

EEE virus is the most neuropathogenic arbovirus present in the U.S. Although most infections will be subclinical, if illness occurs it can be severe. There are two clinical syndromes that can occur. Systemic illness is characterized by an abrupt onset of fever, chills, malaise, arthralgia and myalgia. Symptoms typically last one to two weeks, and recovery is usually complete.

EEE virus infection can also cause an encephalitic illness. When this occurs in infants, the onset is usually abrupt. In children and adults, onset usually occurs after a few days of systemic illness. Symptoms include: fever, headache, irritability, restlessness, drowsiness, anorexia, vomiting, diarrhea, cyanosis, convulsions and coma. Death occurs in about one-third of patients, usually within two to 10 days. Survivors often have disabling neurologic sequelae.

West Nile Virus
West Nile virus was first detected in Vermont in 2000. Although the last human case was reported in 2003, West Nile virus has been detected in birds or mosquitoes every year since.

Eighty percent of West Nile virus infections are subclinical. Approximately 20 percent 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 percent of infections, neuroinvasive disease develops, and clinical syndromes ranging from febrile headache to aseptic meningitis to encephalitis may occur. This is most common in patients older than 50. Symptoms may include fever, gastrointestinal symptoms, ataxia and extrapyramidal signs, optic neuritis, seizures, weakness, change in mental status, myelitis and 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.

Diagnostic Testing
Testing for West Nile virus and EEE virus is available at commercial laboratories or through the Vermont Department of Health Laboratory. CSF or serum can be tested for IgM antibodies. Samples collected during the first seven to 10 days of illness may be negative.

For more information about testing see:

Report Cases to the Health Department
Confirmed cases of WNV and EEE are reportable to the Vermont Department of Health. Report cases to the Epidemiology Program at (802) 863-7240.

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