California has accounted for 33 percent of the at least 60 confirmed human West Nile virus (WNV) cases reported nationally, according to data from the Centers for Disease Control and Prevention (CDC) and the California Department of Public Health (CDPH).


The Golden State has reported 20 human WNV cases to date from the following counties: Butte (1), Contra Costa (1), Fresno (4), Kern (1), Lake (1), Orange (3), Solano (1), Stanislaus (5) and Tulare (3).

In total, 35 counties have reported WNV in mosquitoes, birds or humans.

WNV is spread by the bite of an infected mosquito. Mosquitoes are WNV carriers that become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals when they bite. Rarely, WNV also has spread through transfusions, transplants, and mother-to-child.

Approximately 80 percent of people who are infected with WNV will not show any symptoms at all. Up to 20 percent of the people who become infected will display mild symptoms, which appear 3-14 days after getting infected, and include fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms typically last a few days.

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. Prevention is by avoiding mosquito bites and eliminating mosquito breeding sites. For more infectious disease news and informationvisit and “like” the Infectious Disease News Facebook page

To date, three people have died from complications due to WNV–Arizona, Louisiana and Missouri.

Nationally in 2013, the Centers for Disease Control and Prevention (CDC) reported 2,374 WNV cases and 114 deaths. This was a far cry from the 2012 outbreak that had a final total of  5,674 cases of West Nile virusdisease in people, including 286 deaths.