The past few decades have been marked by the appearance of many new, deadly diseases: HIV, ebola virus, SARS and drug-resistant tuberculosis, to name a few. Scientists now know where each of these diseases emerged. For example, they know SARS probably came first from bats in East Asia, crossed into other mammals and eventually got into humans. HIV is strongly suspected to have crossed into humans from primates. Is there a pattern in the emergence of these diseases? As Rose Hoban reports, scientists now say there is.

Columbia University's Marc Levy was part of an international group of researchers looking at new diseases. The deputy director of the Center for International Earth Science Information Network explains that they compiled a database of 335 emerging pathogens, and then plotted the locations of where each one emerged onto a world map. "And then we combined information about some of these other risk factors - human population density, wildlife density, and we look at a few other factors as well - to see what the correlations were."

What Levy and his co-authors discovered was that there are some places where new diseases are more likely to come from.

They found two factors driving the emergence of these diseases. One is a fast-growing, densely packed human population. "The other factor that we can quantify is the number of wild mammal species that are present," Levy says. "The more of these that are nearby human populations, the greater the risk that some pathogen in those wild animals will cross over into humans."

Levy and his colleagues found many of the hotspots are in regions like East Asia, some of the high population centers in sub-Saharan Africa, parts of South America, where large numbers of human populations are growing next to areas of high wildlife populations.

Modern technology can also drive the development of disease, for example, misuse of antibiotics spurred the development of multi-drug resistant TB.

Levy says the goal behind compiling the map is to push health planners to allocate more resources to disease surveillance and prevention. He says it could be possible to anticipate new diseases, instead of waiting to react until after the disease has spread among humans.

"A century ago, this is where all the glamour was; going out to try to find a way to control or cure yellow fever, and polio, and smallpox was an exciting thing for people to do and to define their careers in terms of. And that fell away," Levy notes. "We're hoping that a new generation will see these as really big challenges to tackle ? because we now have the kind of tools and computer models and global databases that let us actually make progress at doing this."

Levy's paper and the map of emerging disease were published in the journal Nature.