Mosquito samples taken in the Monticello neighborhood that sits on the Southlake/Colleyville border and in Northwest Colleyville's Jefferson Circle area tested positive for West Nile Virus last week.

City officials say the two areas have been treated with a larvicide and will continue to be monitored. In the meantime, the city and the Tarrant County Public Health Department will continue testing samples from throughout the cities.

Area health officials, who say last year's drought followed by a mild winter and recent rainfall has made this a particularly bad season for West Nile, have been testing for the virus and treating pools throughout the summer. Human cases have already been confirmed in Dallas, Denton, Parker and Tarrant counties, and dozens of mosquito pools throughout the Metroplex have tested positive for West Nile in recent weeks.

So far, three human cases of West Nile have been confirmed in Tarrant County. And officials have now treated areas in Colleyville, Southlake, Hurst, Euless, Richland Hills and Bedford.

In addition to work by city and county officials, city leaders are asking residents to be proactive in the fight against mosquitoes and West Nile by following the Four D's:

—DRAIN standing water: Change the water in pet dishes and replace bird bath water weekly; drill holes in in tire swings to allow them to drain; and keep children's wading pools empty and on their side when they're not being used

—Use an insect repellant containing DEET

—Stay indoors during DUSK and DAWN, as those times are when mosquitos are most active

—DRESS in long sleeves and pants when you are outside.

To help residents keep their neighborhoods mosquito free, Southlake is also making biological mosquito larvicide available on a first come, first serve basis — one per household — at the Southlake Community Center, 400 N. White Chapel Blvd., and the Public Works Operations, 1950 E. Continental Blvd.

The larvicide will not affect fish plants or people, but it kills mosquito larve on the surface of standing water for a 30-day period.

West Nile virus is commonly found in Africa, West Asia and the Middle East, and can infect humans, birds, mosquitoes, horses and other animals. The virus passes through the bites of infected mosquitoes, and its incubation period in humans is three to 14 days. Though many people infected will not have any signs of the illness, those who do may experience fever, head and body aches, and occasionally a skin rash on their torso or swollen lymph glands.

More severe symptoms, seen in about one of every 150 cases, can include high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness or paralysis.