The California West Nile virus (WNV) outbreak has increased by another 53 cases during the past week, bringing the Golden State’s total to 428.

West Nile virus
Culex quinquefasciatus

This total year-to-date compares the 205 cases seen in 2013 and the 136 case average year-to-date during the past 5 years. California has also reported 15 WNV fatalities.

The new cases were reported from the following counties: Butte (1), Colusa (1), Contra Costa (1), Fresno (3), Los Angeles (18), Merced (1), Orange (18), San Bernardino (3), Santa Clara (1), Stanislaus (2), Tulare (3), and Yolo (1). This is the first WNV human case from Merced County this year.

The total WNV case in Orange County now stands at 157, more than anywhere else in the country.

Nationally, as of September 30, a total of 46 states and the District of Columbia have reported West Nile virus infections in people, birds, or mosquitoes. Overall, 1,177 cases of West Nile virus disease in people have been reported to CDC.

The CDC data is always one week behind the California Department of Public Health data and is reported to be 374, which makes California account for 31% of cases nationally.

West Nile virus is an arthropod-borne virus (arbovirus) most commonly spread by infected mosquitoes. West Nile virus can cause febrile illness, encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord).

It was first detected in North America in 1999, and has since spread across the continental United States and Canada.

Most people get infected with West Nile virus by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the virus to humans and other animals.

In a very small number of cases, West Nile virus has been spread through blood transfusions, organ transplants, and from mother to baby during pregnancy, delivery, or breastfeeding, according to the CDC. For more infectious disease news and information, visit and “like” the Infectious Disease News Facebook page