CONTRA COSTA COUNTY -- A group of mosquitoes, a chicken and three crows have tested positive for West Nile virus, prompting officials to remind people to protect themselves against the potentially fatal illness, the Contra Costa Mosquito & Vector Control District said Tuesday.

The infected mosquitoes and a chicken were found over the last two weeks in Holland Tract, an area near Brentwood. Three dead crows that tested positive for the deadly virus were also found in Brentwood on June 20, in Antioch on June 25 and in San Ramon on June 26.

"This is not surprising given the amount of West Nile virus activity in our neighboring counties right now," said Deborah Bass, a spokeswoman for the district. "It only takes one bite from an infected mosquito to transmit the virus."

The Contra Costa Mosquito & Vector Control District will fog along the Martinez waterfront Wednesday morning in an attempt to reduce the spread of the virus.

West Nile virus symptoms include fever, headache, fatigue, body aches, and swollen lymph glands. Symptoms typically last several days but can be more severe for those older than 50 or those with diabetes or hypertension.

To avoid being bitten by mosquitoes and infected with West Nile, public health officials suggest the following measures:

  • Avoid activity outside when mosquitoes are most active, especially at dawn and dusk.

  • When outdoors, wear long pants, long-sleeve shirts and other protective clothing.

  • Apply insect repellent that contains DEET, picaradin, oil of lemon eucalyptus or IR3535 in accordance with label instructions.

  • Make sure that doors and windows have tightfitting screens. Repair or replace screens that have tears or holes.

  • Eliminate all sources of standing water that can support mosquito breeding.

  • Contact Contra Costa Mosquito & Vector Control if there is a significant mosquito problem where people live or work, including abandoned swimming pools.

  • Report dead birds by calling 877-WNV-BIRD (877-968-2473).

    For details about the West Nile virus, go to http://cchealth.org/westnile or http://westnile.ca.gov.

    Since 2005, 47 people in Contra Costa County have been diagnosed with West Nile virus, including one person last month, and two have died.

    Follow Karina Ioffee at Twitter.com/kioffee.