A man and woman are the first two people to be infected with West Nile virus so far this year in Fresno County, and two men are the first cases in Tulare County, prompting health warnings for people to avoid mosquito bites.

Both of the people in Fresno County were ill enough to be hospitalized and one remained in the hospital Friday, a county health official said. In Tulare, one man required hospital care and also remained in the hospital.

The Fresno and Tulare county cases are among six West Nile cases statewide confirmed this week, and among seven so far this year in the state. According to the state Department of Public Health, two people from Stanislaus County also were infected this week. And an infection in Santa Barbara County was reported earlier.

In 2010, Fresno County reported a total of 23 people with West Nile infections and one virus-related death. Tulare County had 12 cases and no deaths. Madera County had seven cases and two people died. Kings County had one case and no deaths.

"We've averaged at least one death for the last six years," said David Luchini, manager of the communicable disease division at the Fresno County Department of Public Health.

West Nile virus is spread to humans and animals through mosquito bites. The risk of serious illness to most people is low, but in some cases – about 1% – the virus can cause serious neurologic illnesses, such as encephalitis or meningitis.

Health officials would not identify the people infected with West Nile, as to not violate their privacy. But one of the Fresno County people infected lives in a rural area of northwest Fresno, said Tim Phillips, manager of the Fresno Mosquito and Vector Control District. Mosquito control officials are checking the area for mosquitoes, he said.

Health officials confirmed the other person lives in Clovis, within the Consolidated Mosquito Abatement District, which includes parts of Clovis and Selma, as well as Kingsburg, Fowler, Sanger, Orange Cove and Reedley.

Consolidated manager Steve Mulligan said mosquitoes have tested positive for the virus throughout the district.

"People anywhere in the Valley need to know West Nile-carrying mosquitoes could be present and need to protect themselves from mosquito bites when outside, particularly from dusk through the night until dawn," he said.