Virginia Department of Health officials announced last Thursday that a pool of standing water in Henrico County tested positive for the mosquito-borne West Nile Virus (WNV). According to the VDH, Henrico officials collected mosquitoes on July 13. The state's Division of Consolidated Laboratory Services reported that the mosquito pool tested positive for the virus on July five days later. VDH officials found that no humans were infected with the virus. This most recent incident marks the reappearance of WNV, which has been detected every year in the Commonwealth since 2000. According to the U.S. Centers for Disease Control and Prevention (CDC), over 15,000 people in the U.S. have tested positive for the infection since 1999, including over 500 deaths. About one in 150 people infected with WNV will develop serious illness, including inflammation of the brain. Severe symptoms include high fever, headache, disorientation, vision loss and paralysis. The effects may last several weeks and can cause neurological damage. Earlier this month, the VDH issued a public health advisory for Eastern Equine Encephalitis (EEE) in the Hampton Roads area of Virginia. Mosquitoes contracted the virus from horses and other livestock. While vaccines exist for horses, humans remain at risk. Executive Director of Student Health James Turner stressed the need to eliminate mosquito breeding grounds to prevent proliferation of West Nile. "To avoid mosquito bites, we must remove any standing water from our homes," Turner said. "There can be no water in old tires or children's toys, and screens must be functional." Infected mosquitoes are the most common transfer of the infection. The parasite spreads the illness it acquires from infected birds to humans and other animals. According to the CDC, a small number of cases have come through blood transfusions, organ transplants, breastfeeding, and even pregnancy. West Nile, however, is not spread through casual contact. Randy Buchanan, environmental engineer for Henrico County's Standing Water Initiative, said he believes knowledge of the environment remains the best course of action for preventing WNV infections. "People should not panic and instead remain aware of mosquitoes in their surroundings," he said. "Nearly 85 percent of mosquitoes are breeding in hidden locations." Local doctors warn that no matter how a person contracts WNV, symptoms should be addressed quickly. "Often times the patient feels some sense of weakness or paralysis, and they should see a doctor immediately," said Bill Petri, division chief of Infectious Disease at the University Medical Center. "We don't know if there is an effective remedy for West Nile Virus, so the earlier the treatment, the better the outcome." The CDC cautions that while people over 50 are more susceptible to West Nile, simply being outside puts anyone at risk. "Walk your property once a week, and empty anything with standing water," Buchanan said. "Mosquitoes can live in as little as two tablespoons of water." The CDC Web site also lists steps to prevent mosquito bites and the West Nile Virus in addition to removing sources of standing water. These include wearing insect repellant containing the chemical DEET, wearing long sleeves, and avoid being outside during dusk and dawn -- the times of highest mosquito activity. According to the CDC, The West Nile Virus originated from an adult woman in the West Nile District of Uganda in 1937. In 1957, a case in Israel determined the illness a cause of severe human meningitis (swelling of the spinal cord) and encephalitis.The virus appeared in horses in the 1960's and touched North American soil in 1999.