State health officials have launched their annual campaign to track down and limit the spread of the West Nile virus. Officials with the Connecticut Agricultural Experiment Station, which monitors mosquito populations and the diseases they carry, have been trapping the pests in parts of Stamford. They say this summer is likely to be an active bug season given the mild winter and springtime rains. Experts say residents should keep screens on their open windows and clear out any standing water on their properties. They also recommend bug repellant containing DEET.