That or some recent traveler to malaria endemic areas inadvertently brought back mosquitoes somehow, which sounds highly improbable but hey, tarantulas travel to strange places in crates of bananas all the time.
My grandmother grew up in the Tidewater, and suffered recurrent malaria as a child. I just looked it up and learned that malaria played a part in winning the Revolution ;-)
http://www.washingtonpost.com/wp-dyn/content/article/2010/10/18/AR2010101803877.html