So far the mosquito-borne disease also has turned up in birds in New York, Maryland, Connecticut, Massachusetts, Rhode Island, and Pennsylvania. Last year, when the virus first surfaced in the Western Hemisphere, seven people died and 55 were infected in the New York City area. Paul Epstein of Harvard Medical School, writing in Scientific American , ascribes part of the cause to global warming, which induces hot summers, mild winters, and drought. Drought in spring and summer concentrated nourishing organic matter in their breeding areas and simultaneously killed off mosquito predators, such as lacewings and ladybugs, that would otherwise have helped limit mosquito populations. Drought would also have led birds to congregate more as they shared fewer and smaller watering holes, many of which were frequented, naturally, by mosquitos.
Ships are a major means of microbe transportation.
According to the journal Nature , there have been significant concentrations of a type of cholera that can cause fatal intestinal illness in the ballast water of freighters landing in Norfolk and Baltimore over the last three years. Scientists don't think the Chesapeake is a good incubator for this type of cholera, but they are worried that freighter traffic could turn out to be a hidden conduit for deadly diseases from abroad. Ships often have been implicated as carriers of imported diseases. Take the case of the Asian long-horned beetle, which currently is eating its way out of Brooklyn and elsewhere on Long Island onto the mainland. It is thought that this beetle came to the U.S. in crating on ships.