A wild bird collected in the county last month tested positive for West Nile virus, health officials said today. The bird was found in the last week of October in Simi Valley, according to the Ventura County Environmental Health Division. Mosquitoes carry the virus, and birds, horses and people can be infected. To minimize exposure to the virus, officials say, people should eliminate standing water from their property, make sure exterior doors and windows have tightfitting screens without holes, limit outdoor activity at dawn and at dusk when mosquitoes are most active, wear long pants and long-sleeved shirts when outdoors and use insect repellent. Call 658-4310 to report potential mosquito-breeding sources to the county. People also are encouraged to report crows, ravens and birds of prey that have died recently to the state Department of Public Health at 877-968-2473.