For the fourth year in a row, the United States has reported more than 2,000 human West Nile virus (WNV) cases and California once again leads all states.

As of last week, 2,022 cumulative WNV cases have been reported, including 114 deaths. The last year the US saw less than 2,000 cases was 2011 (712).


California has reported 707 cases to date, followed by Texas (248), Colorado (101) and Arizona (92).

In addition, this is not the first time California reported the most WNV cases in the nation. Since reporting the first human case in 2002, California has topped the country in cases in 2004 (779), 2005 (880), 2008 (445), 2011 (158), 2013 (379) and last year (801).

West Nile virus is a mosquito-borne disease that can cause encephalitis, a brain inflammation. West Nile virus was first detected in North America in 1999 in New York. Prior to that it had only been found in Africa, Eastern Europe, and West Asia.

According to the CDC, approximately 80 percent of people (about 4 out of 5) who are infected with WNV will not show any symptoms at all.

Up to 20 percent of the people who become infected have symptoms such as fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though even healthy people have become sick for several weeks.

About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent.

There is no specific treatment for WNV infection.

Robert Herriman is a microbiologist and the Editor-in-Chief of Outbreak News Today and the Executive Editor of The Global Dispatch

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