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Delaware Health Alert Network #119

June 2, 2006 11:23 AM

Health Advisory

The Delaware Division of Public Health (DPH) is providing the following information to the medical community concerning West Nile Virus (WNV) infection.

Although no human cases have been reported this year in Delaware, WNV is endemic in our region and cases may occur any time there is mosquito activity.

The diagnosis of WNV and other arboviral diseases (such as St. Louis Encephalitis and Eastern Equine Encephalitis) are required by law to be reported to DPH. Reports can be made by calling 888-295-5156 or 302-744-4541.


Delaware's first confirmed human case of WNV occurred in 2002. During 2003, seventeen human cases, two of which resulted in deaths, were reported. There were no reported human cases in 2004 but two were reported in 2005. Additionally, multiple birds and horses tested positive during this time.

It is suspected that many cases went unreported due to clinically inapparent symptomology.

Clinical Description

Arboviral infections may be asymptomatic or may result in febrile illnesses of variable severity sometimes associated with central nervous system (CNS) involvement (Neuroinvasive or Non-Neuroinvasive). During CNS involvement, clinical syndromes include meningitis, myelitis and encephalitis, which are clinically indistinguishable from similar syndromes caused by other viruses.

Neuroinvasive Disease:

  • Arboviral meningitis is usually characterized by high fever, headache, nuchal rigidity, and pleocytosis in cerebrospinal fluid.
  • Arbomeylitis is usually characterized by fever and acute bulbar or limb paresis or flaccid paralysis.
  • Arboviral encephalitis is usually characterized by fever, headache, and altered mental status ranging from confusion to coma, with or without additional signs of brain dysfunction.
  • Less common neurological syndromes can include cranial and peripheral neuritis or other neuropathies, including Guillain-Barre` syndrome.
  • Clinical criteria for diagnosis - Requires the presence of fever and at least one of the following: acutely altered mental status, signs of central or peripheral neurologic dysfunction, or pleocytosis associated with illness clinically compatible with meningitis.

Non-Neuroinvasive Disease:

  • May cause febrile illnesses (West Nile Fever) that are non-localized, self-limited illnesses with headache, myalgias, arthralgias, and sometimes accompanied by skin rash or lymphadenopathy. Laboratory confirmed illnesses lacking documented fever can occur, and overlap among the various clinical syndromes is common.
  • Syndromes caused by these usually neurotropic arboviruses can rarely include myocarditis, pancreatitis, or hepatitis.
  • Clinical criteria for diagnosis - Requires, at a minimum, the presence of documented fever, the absence of neuroinvasive disease, and the absence of a more likely clinical explanation for the illness. Involvement of non-neurological organs (heart, pancreas, liver, etc.) should be documented using standard clinical and laboratory criteria.

Case Classification

DPH will classify human cases as either confirmed or probable, according to the following laboratory criteria:


  • Four-fold or greater change in virus-specific serum antibody titer, or
  • Isolation of virus from tissue, blood, CSF or other sterile body fluid, or
  • IgM antibodies demonstrated in CSF by EIA, or
  • IgM antibodies in serum by EIA and confirmed by IgG antibodies in the same or a later specimen by another serologic assay.
  • PCR confirmation with positive IgM antibodies


  • Less than or equal to a two-fold change of virus-specific serum antibodies, or
  • IgM antibodies demonstrated in serum by EIA but with no available results of a confirmatory test for IgG antibodies.

DPH Diagnostic Testing

DPH Laboratory (DPHL) performs WNV testing for humans, birds and horses. Methods include antibody testing and confirmatory neutralization, as well as PCR and culture. Specimens 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 (i.e., Yellow Fever, Japanese Encephalitis, Dengue)

  • Please contact DPH Epidemiology at 1-888-295-5156 or 302-744-4541 to coordinate testing.
  • All WNV testing should be performed at, or confirmed by, DPHL.
  • Patient samples obtained at hospital labs in Delaware should automatically be sent to DPHL for confirmatory testing.
  • Healthcare providers may request WNV testing from commercial laboratories. However, these results should be confirmed by DPHL because some commercial laboratories have reported high false positive rates in the past. This may necessitate the patient have a second serum sample drawn. Patients can have serum samples drawn at Delaware State Service Centers. Please contact DPH Epidemiology to arrange for this service.

For Further Information

  • For questions about human WNV infection and to report suspected cases, contact DPH Epidemiology at 888-295-5156 or 302-744-4541.
  • Centers for Disease Control and Prevention:
  • For general information regarding mosquito control, contact the Department of Natural Resources and Environmental Control at 302-739-3493
  • To report sick or dead wild birds, contact Department of Natural Resources and Environmental Control Mosquito Control:
    • New Castle County - 302-836-2555
    • Kent or Sussex Counties - 302-422-1512

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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