The deadly outbreak of an illness that used to infect only animals but now jeopardizes the survival of all humanity has long been a standard thriller movie plot (think Contagion or the 1995 classic Outbreak). Whereas reality usually unfolds at a slightly less frenetic pace, the growing threat from emerging diseases is nonetheless very real. Over the past three decades we have witnessed the appearance of HIV/AIDS, mad cow disease, H5N1 (avian flu) and the brain-damaging Nipah virus—just to name a few. More recently, obscure poxvirus infections such as monkeypox and cowpox have started to expand their borders.

Mounting population pressures and the spread of rapid global transportation are fueling the emerging infections trend. Tracing the chain of unintended consequences that lead toward illness can be quite difficult, however. To give one example: Lyme disease took off in the northeastern U.S. as more and more people moved to previously wooded areas, displacing the wolves who used to keep coyotes in check, thereby limiting the number of the foxes (who can't compete with coyotes) who had hunted the mice that had become infested with deer ticks; with fewer foxes, more mice survived to spread the Lyme disease spirochete Borrelia burgdorferi to people.

A few scientists (not as many as you might hope) are trying to keep tabs on where these emerging diseases are sickening people and when the obscure pathogens might be building up to unleash a pandemic. Scientific American highlights the work of one of them, Anne W. Rimoin, an assistant professor of epidemiology at the University of California, Los Angeles, School of Public Health, in its March feature "New Threat from Poxviruses." In the following two-and-a-half minute video, Rimoin, talks about her work tracing monkeypox infections in the Democratic Republic of the Congo.

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