Mosquito season is back, and so is concern among health authorities about the West Nile virus.

The public was asked this week by the Seattle-King County Public Health Department to contact it with any reports of dead birds. Crows in particular die quickly from West Nile virus, which is spread to people and horses through bites of infected mosquitoes, and clusters of dead crows may indicate cases of the virus, officials.

Reports can be filed at (206) 205-4394 or or www.metrokc.gov/health/westnile/deadbird.htm.

West Nile virus wasn’t found in King County last year, though in past years birds and horses have died here from the virus. The infection can be asymptomatic, but it can also cause mild to severe symptoms, including diseases of the brain and spinal column.

“It’s difficult to predict” if West Nile “will be a problem in our area this year,” said Dr. David Fleming, director of the Health Department. “But it’s a good idea to protect your family by eliminating mosquito habitat from your property and taking precautions to avoid being bitten by mosquitoes.”

Beginning this week, Fleming said, some dead birds that are reported will be collected for laboratory testing for West Nile. So will batches of mosquitoes trapped at locations throughout King County.

A mosquito becomes infected with West Nile by biting an infected bird that carries the virus. Horses are susceptible to West Nile, which can result in severe disease or death. Horse owners should contact their veterinarian for a vaccine for horses.

West Nile isn’t spread by person-to-person contact, nor is it transmitted directly from birds or other animals to people.

Mosquito season, when West Nile virus is of most concern, runs from spring through late fall.

Nationally in 2007, 3,630 cases of human West Nile casee were reported from 44 states, and 124 people died. People of all ages can get the disease, but people over 50 are more likely to become seriously ill, according to authorities.

Authorities said the mosquito that is most likely to infect King County residents with West Nile virus is Culex pipiens, or the northern house mosquito. It prefers to lay eggs in small amounts of standing water around houses. Tips for reducing those conditions include:

• Tip out containers that collect water, including barrels, buckets, wheelbarrows, bottles, and plant saucers.

• Empty children’s wading pools when not in use and change water in birdbaths and animal troughs at least once a week.

• Dump water off of tarps and plastic sheeting and get rid of used tires.

• Clean garden ponds, circulate water in fountains and cover rain barrels with mosquito screens.