West Nile Virus (WNV) was first reported in North America during the summer of 1999.  WNV infection should be considered in any patient with a febrile or acute neurologic illness and a history of recent mosquito bite, blood transfusion, or organ transplant especially during summer months. According to CDC, 70-80% of human infections are subclinical. WNV is not transmissible from person to person.

As of August 25, 2015, 44 states and the District of Columbia have reported West Nile virus infections in people, birds, or mosquitoes. Overall, 38 states have reported 303 cases of West Nile disease in people to the CDC. Half of these cases were classified as neuroinvasive.

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 (e.g. yellow fever, dengue) may have false positive WNV antibody tests. Although PCR testing is available, it is not very sensitive for diagnosis of WNV.

CDC offers a dynamic map viewer that shows WNV cases in each state.

http://diseasemaps.usgs.gov/mapviewer/


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