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Delaware Health Alert Network #33

July 1, 2003 7:53 am

Health Advisory

Delaware's Division of Public Health (DPH) announces the first wild bird to test positive for West Nile Virus (WNV) in 2003. The dead crow, collected on June 23, was found in the Newark area. This is the first bird to test positive in the 2003 season. This advisory provides information to the Delaware health care community about WNV.

WNV is endemic in Delaware. 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.

There were 4,156 confirmed human WNV cases nationwide in 2002, including 284 deaths, according to the Centers for Disease Control and Prevention (CDC). Nationally, WNV has spread to 44 states in the last four years.


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 10% 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.


Humans are infected with WNV via the bite of an infected mosquito. In a very small number of cases, WNV has been spread through blood transfusions, organ transplantation and during pregnancy from mother to baby. Aside from these specific circumstances, it does not spread from person to person.

Incubation Period

The incubation period is thought to range from three to 14 days.

Signs and Symptoms

  • Mild - Most WNV infections (80%) are clinically unapparent. Approximately 20% of those infected develop a mild illness (West Nile Fever), which includes sudden onset of fever and which may be accompanied by malaise, anorexia, headache, myalgia, nausea, vomiting, rash, lymphadenopathy, and eye pain. Symptoms generally last three to six days.
  • Severe - 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.

Clinical Suspicion

Diagnosis of WNV infection is based on a high index of clinical suspicion and obtaining specific laboratory tests. WNV should be strongly considered in adults > 50 years of age who develop unexplained encephalitis or meningitis in summer or early fall. Local evidence of 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 WNV testing. The most efficient diagnostic method is detection of IgM antibody to WNV in serum or cerebral spinal fluid (CSF), collected within eight days of illness onset, using the IgM antibody capture enzyme-linked immunosorbent assay (MAC-ELISA). Since IgM antibody does not cross the blood-brain barrier, IgM antibody in CSF strongly suggests central nervous system infection. False-positive results may occur in patients recently vaccinated for or recently infected with related flaviviruses (e.g., yellow fever, Japanese encephalitis, dengue).


Treatment is supportive, often involving hospitalization, intravenous fluids, respiratory support, and prevention of secondary infections for patients with severe disease. Ribavirin in high doses and interferon alpha-2b were found to have some activity against WNV in vitro, but no controlled studies have been completed on the use of these or other medications, including steroids, antiseizure medications, or osmotic agents, in the management of WNV encephalitis.

Reporting Suspected Human WNV Infection

Please report suspected human WNV infections to DPH at 888-295-5156.

Additional Information

The following website contains information about resources locally, including how to submit clinical specimens and birds for testing.


The following is the WNV website at the CDC.

Questions about this advisory should be directed to DPH at 888-295-5156.

Categories of Health Alert messages:

  • Health Alert: Conveys the highest level of importance; warrants immediate action or attention.
  • Health Advisory: Provides important information for a specific incident or situation; may not require immediate action.
  • Health Update: Provides updated information regarding an incident or situation; unlikely to require immediate action.
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