In 2000, West Nile virus appeared for the first time in Pennsylvania in birds, mosquitoes and a horse. To combat the spread of West Nile virus, which is transmitted by mosquitoes, Pennsylvania has developed a comprehensive network. This network, which covers 40 counties, includes trapping mosquitoes, collecting dead birds and monitoring horses, people and, in past years, sentinel chickens. Please explore the PA West Nile Virus Control Program Website to find out more about how you can help, to learn about West Nile virus or the latest surveillance update from your area.