West Nile Virus 2015
West Nile Virus (WNV) is an arbovirus, first reported in North America in the summer of 1999. According to CDC, 70-80% of human WNV infections are subclinical. However, WNV infection should be considered in any patient with a febrile or acute neurologic illness and recent mosquito exposure, blood transfusion, or organ transplant especially during summer months. WNV is not transmissible from person to person.
As of June 16, 2015, thirteen states have reported West Nile virus infections in people, birds, or mosquitoes. Four cases of human infections have been reported to CDC. These cases occurred in Kansas, Texas, New Mexico, & Oklahoma. Half of these cases were classified as neuroinvasive disease, such as meningitis or encephalitis.
The diagnostic test of choice for WNV and other arboviral infections is serologic analysis of serum or CSF for IgM and IgG antibodies. IgM antibody to WNV can be detected as early as 4 days after onset of illness and may persist for several weeks. Since IgM antibody does not cross the blood-brain barrier, its presence in CSF strongly suggests central nervous system infection. IgG antibody to WNV may be detectable one week after illness onset. Patients who have been vaccinated against, or infected with, related flaviviruses (yellow fever, dengue) may also have positive WNV antibody tests. Although PCR testing is available for WNV, it has been found to be relatively insensitive for diagnosis. Specimen requirement is one red top tube of blood or 1.0 mL CSF.
