At the viral chatter stage of an outbreak, pathogens are just starting to infect people in sporadic bursts. It's a sign that a pandemic may be on the horizon.
Disease forecasts are like weather forecasts: We cannot predict the finer details of a particular outbreak or a particular storm, but we can often identify when these threats are emerging and prepare accordingly. The viruses that cause avian influenza are potential threats to global health. Recent animal outbreaks from a subtype called H5N1 have been especially troubling to scientists. Although human infections from H5N1 have been relatively rare, there have been a little more than 900 known cases globally since 2003 — nearly 50% of these cases have been fatal — a mortality rate about 20 times higher than that of the 1918 flu pandemic. If the worst of these rare infections ever became common among people, the results could be devastating. Approaching potential disease threats from an anthropological perspective, my colleagues and I recently published a book called " Emerging Infections: Three Epidemiological Transitions from Prehistory to the Present " to examine the ways human behaviors have shaped the evolution of infectious diseases, beginning with their first major emergence in the Neolithic period and continuing for 10,000 years to the present day. Related: How to avoid bird flu Viewed from this deep time perspective, it becomes evident that H5N1 is displaying a common pattern of stepwise invasion from animal to human populations. Like many emerging viruses, H5N1 is making incremental evolutionary changes that could allow it to transmit between people. The periods between these evolutionary steps present opportunities to slow this process and possibly avert a global disaster. Spillover and viral chatter When a disease-causing pathogen such as a flu virus is already adapted to infect a particular animal species, it may eventually evolve the ability to infect a new species, such as humans, through a process called spillover . Spillover is a tricky enterprise. To be successful, the pathogen must have the right set of molecular "keys" compatible with the…