What FPs need to know about West Nile virus disease
The FDA recently approved a commercial product, the PanBio West Nile virus IgM assay, which correctly identified the antibody in 90%–99% of cases. IgM antibody does not cross the blood-brain barrier, so its detection in cerebrospinal fluid is presumptive evidence of central nervous system infection.
Other laboratory findings include:
- normal or increased white blood cell counts, sometimes with lymphopenia or anemia
- occasional hyponatremia, especially in patients with encephalitis
- cerebrospinal fluid pleocytosis (usually lymphocytic), increased protein and normal glucose
- normal computed tomography brain scans
- abnormal magnetic resonance images in one third of patients.
Treatment is supportive
Treatment of severe disease is supportive. No evidence indicates efficacy of ribavirin, interferon, steroids, or other agents.
How to use public health resources
Prevention of West Nile virus disease will require both clinical and public health efforts. A good surveillance system is vital, providing clinicians and the community with knowledge about disease activity in birds and humans.
- Local or state health departments must coordinate, investigate, and track reports of dead birds by community members.
- Clinicians must notify the health department about suspected infections in humans.
- By publicizing the results of an active surveillance program, the health department assists clinicians in identifying cases more quickly and helps motivate the community to take appropriate preventive measures.
In late August 1999, an infectious disease specialist reported 2 patients with encephalitis at 1 hospital in Queens to the New York City Department of Health. An ensuing investigation revealed 6 additional cases at nearby hospitals. The illnesses were characterized by fever, severe muscle weakness (7 of 8 persons), and flaccid paralysis (4 of 8). Cerebrospinal fluid test results suggested viral infection.
So began the saga of human West Nile virus in the United States.
The virus was first isolated from a patient in Uganda, and is now distributed throughout Africa, the Middle East, parts of Europe, southwestern Asia, and Australia. Disease outbreaks in other parts of the world were infrequent until 1996.
West Nile virus is thought to have come to North America from Israel, but it is not clear how. Since 1999, the virus has spread rapidly throughout the US. Interestingly, the number of human cases reported annually was low (20–60) until 2002, when more than 4000 cases were reported. Only 9 continental states had avoided human cases of West Nile virus, and only 4 had reported no human or animal cases.
Correspondence
1601 Parkview Avenue, Rockford, IL 61107. E-mail: ehenley@uic.edu
