The season's first cases of the West Nile Virus have been reported the past few weeks in places like Colorado and Pennsylvania. But lest you worry too much, take note: The U.S. Centers for Disease Control (CDC) says the virus, transmitted by infected mosquitoes, is harmless to most people and that 80 percent who have it show no symptoms. The most vulnerable are infants, young children, the elderly and those with compromised immune systems. The CDC says that about one in 150 people stricken with the infection develop serious symptoms, which may include high fever, nausea, convulsions and temporary paralysis. Although it rarely is fatal, seven out of the 576 people in Colorado confirmed to have the disease died last year, for example. Birds, especially crows and robins, are known to harbor the virus, and mosquitoes become carriers when they feast on their carcasses. Worried? Then you might want to toss some insect repellent in your beach bag.