Health Advisory
EASTERN EQUINE ENCEPHALITIS AND WEST NILE VIRUS

The Delaware Division of Public Health (DPH advises the health care community of evidence of Eastern Equine Encephalitis (EEE) in areas of Maryland bordering Delaware). In addition, DPH reminds health care providers that West Nile Virus (WNV) is endemic in Delaware.

Eastern Equine Encephalitis, Maryland

The Maryland Department of Health and Mental Hygiene (DHMH) has confirmed Eastern Equine Encephalitis (EEE) in two Maryland horses. Brain tissue samples from two Worcester County horses, submitted for laboratory testing on July 21 and July 23, were confirmed positive and reported on July 28, 2003. Neither horse is known to have been vaccinated against EEE. In addition, the Maryland DHMH reports the detection of EEE in a mosquito pool collected from Wicomico County, Maryland. EEE activity has not yet been detected in Delaware.

In humans, typical symptoms of EEE include fever, headache, mental confusion, vomiting, extreme tiredness, muscle aches, and sometimes seizures and coma. Symptoms usually occur 4 to 10 days after exposure to an infected mosquito. There is no specific treatment and no vaccine for use in humans. Although EEE occurs less frequently than WNV, it can be far more devastating to human health. Up to 30 percent of EEE infected persons who develop neurologic symptoms may die compared to fewer than 10 percent who die following WNV neurologic illness.

West Nile Virus, Delaware

The Delaware Department of Agriculture (DDA) reports the death of a horse from WNV. The horse, from Harrington Delaware, was diagnosed at the University of Pennsylvania. WNV is endemic in Delaware. As of August 4, 2003, the DPH Laboratory has identified WNV in 24 wild birds submitted this year (15 from New Castle County, 7 from Kent County, and 2 from Sussex County). The disease first appeared in Delaware birds and horses in 2000. Delaware's first and only confirmed human case of WNV occurred in 2002, and was not fatal. In 2002, 214 wild birds tested positive for WNV in Delaware, as did six mosquito samples and 24 horses.

Most WNV infections (80 percent) are clinically inapparent. Approximately 20 percent of those infected develop a mild illness (West Nile Fever), which includes sudden onset of fever which may be accompanied by malaise, anorexia, headache, myalgia, nausea, vomiting, rash, lymphadenopathy, and eye pain. Symptoms generally last three to six days. Approximately 1 in 150 infections result in severe neurological disease, more commonly encephalitis than meningitis. The most important risk factor for developing severe neurological disease is advanced age. Neurologic presentations have included ataxia and extrapyramidal signs, optic neuritis, cranial nerve abnormalities, polyradiculitis, myelitis, and seizures. Several patients experienced severe muscle weakness and flaccid paralysis. Other associated symptoms include fever, weakness, and gastrointestinal symptoms. Myocarditis, pancreatitis, and fulminant hepatitis have also been described. The incubation period of WNV is thought to range from 3 to 14 days after the bite of an infected mosquito.

Clinical Suspicion

Diagnosis of EEE and WNV infection is based on a high index of clinical suspicion and obtaining specific laboratory tests. EEE and WNV should be strongly considered when unexplained encephalitis or meningitis occurs in summer or early fall. Local evidence of EEE and WNV enzootic activity or other human cases should further raise suspicion. Obtaining a recent travel history is also important.

Diagnostic Testing

The DPH Laboratory performs EEE and WNV testing for birds, horses and humans. Methods include antibody testing and confirmatory neutralization, as well as PCR, and culture. Detection of IgM antibody in human serum or spinal fluid is an effective method for diagnosing WNV infection. Serum should be collected within eight days of illness onset. False positive antibody results for WNV may occur in patients recently vaccinated for or infected with related flaviviruses (e.g. yellow fever, Japanese encephalitis, dengue). For submission of specimens call the virology laboratory at 302-653-2870.

Treatment

Treatment is supportive, often involving hospitalization, intravenous fluids, respiratory support, and prevention of secondary infections for patients with severe disease.

Prevention

To avoid mosquito bites and reduce the risk of infection, patients should be encouraged to:

• Wear insect repellant containing less than 50% DEET for adults, less than 30% DEET for children;
• Wear long-sleeved shirts and pants in mosquito-infested areas;
• Avoid peak mosquito activity during dusk, evening or early morning;
• Drain or remove items that collect water and provide mosquito-breeding habitat, such as buckets, rain barrels, old tires, blocked rain gutters and unused swimming pools.

Additional Resources

• For questions about EEE and WNV in humans, and to report suspected human cases, call DPH at 888-295-5156.
• To report sick or dead wild birds, call Mosquito Control between 8 a.m. and 4:30 p.m. in New Castle County at (302) 323-4492, and in Kent or Sussex counties, call (302) 422-1512.
• For general information about mosquito control, contact DNREC at (302) 739-3493.
• For questions about animal health, call the Department of Agriculture at 1-800-282-8685 between 8 a.m. and 4:30 p.m., or leave a message after-hours.