Is this what tropical diseases look like in a greenhouse world?

Paraguay had not seen a case of yellow fever since 1974, so it’s no surprise that the current outbreak caught health authorities there short-handed: with only 100,000 does of vaccine available, according to the Associated Press, Paraguay got 50,000 doses from Brazil and is expecting 250,000 from Peru. But there have already been protests, with thousands of worried people blocking highways to demand that vaccine be made widely available.

With five confirmed cases in Paraguay, out of 46 reported, public health officials have their fingers crossed that that are not seeing the leading edge of a disease that spreads to more regions as a result of climate change, as some scientists have long warned.

Yellow fever is one of the tropical diseases (others include malaria and dengue fever) that might spread beyond their current infection zones if the world warms up and rainfall patterns change. The World Health Organization estimates that yellow fever kills 30,000 people worldwide every year, causing fever, vomiting, jaundice and bleeding from the mouth, nose, eyes and stomach. It is carried by at least 14 separate species of the mosquito genus Aedes.

In the past it struck cities as far north and south—that is, non-tropical—as Philadelphia, New York, Boston and Buenos Aires. Clearly, then, factors other than climate determine where and how seriously yellow fever strikes, and it is facile to attribute its appearance to changing climate alone. Still, the concern is that as freeze-free regions expand, disease-carrying mosquitoes will thrive in places they seldom did.