San Gabriel Valley residents are being urged to take precautions while outdoors after tests confirmed West Nile virus activity in three cities in the region, authorities said Tuesday.

Positive tests were confirmed in samples taken from mosquitoes in the city of Arcadia and from three chicken flocks in Arcadia, Irwindale and Monterey Park, according to the San Gabriel Valley Mosquito & Vector Control District.

The samples were collected in the last few weeks from the Los Angeles County Arboretum and Santa Anita Racetrack in Arcadia, the Santa Fe Dam Recreational Area in Irwindale, and an area near Garvey Ranch Park in Monterey Park.

Officials said the tests indicate West Nile activity is increasing throughout the San Gabriel Valley, after earlier being detected in the South Bay, San Fernando Valley and other areas.

“This is important information for people to consider as they prepare for the upcoming holiday weekend,” district manager Kenn Fujioka said in a statement. “Preventing West Nile virus from making you sick is as simple as preventing mosquito bites.”


Earlier this month, West Nile activity forced the indefinite closure of the Madrona Marsh, a 10-acre preserve in Torrance popular with bird-watchers and other recreational users.

The Los Angeles County Department of Public Health has confirmed 46 human infections so far this year, including two fatalities. Five of the cases were in the San Gabriel Valley, officials said.

West Nile is spread through mosquitoes, which get the virus by biting infected birds. August and September are typically peak months for transmission.

Most cases cause mild or no symptoms in humans, but rare cases can lead to serious illness or death.


“We’ve talked to enough people who are sickened by West Nile and they are always amazed that one little mosquito bite can cause such illness,” said Kelly Middleton, a spokeswoman for the San Gabriel vector control district. “People don’t take it seriously enough and folks that get sick can get quite sick.”

Residents were urged to avoid outdoor activity from dusk to dawn -- when mosquitoes are most active -- to wear long sleeves and pants, and apply insect repellent.

ALSO:

Earthquake: Magnitude 4.1 quake strikes near Reno


Rim fire 20% contained, but flames threaten 4,500 structures

Thunderstorms hit mountain, desert areas of Southern California

carla.rivera@latimes.com

Twitter: @CarlaRiveralat