“Five cases of the mysterious Wuhan coronavirus have been confirmed in the United States, giving rise to concerns about a potential global pandemic. We’ve seen this story before, as health authorities working with threadbare data try to walk the line between epidemic readiness and needless panic. Is this new outbreak poised to become the next AIDS pandemic or a new SARS, which was stopped in its tracks after 774 deaths? To cut through the headlines, we can use a simple concept called the “epidemic triangle.” Employed by epidemiologists since the discipline’s earliest days, it is indispensable in predicting whether localized outbreaks will transform into full-blown epidemics.
The epidemic triangle is essentially an equation. It posits that every outbreak, regardless of its specific traits, is dependent on the interplay between three factors: the pathogen (the agent causing infection), the host (the organism at risk of infection) and the environment (the setting where the infections occur). Every single epidemic — be it the flu, cholera or even behavioral epidemics like drunken driving — is the result of a dynamic shift in one of these points of the epidemic triangle, which then causes a domino effect leading to a sudden explosion of new cases.
In one classic example of this phenomenon, we have an environmental shift to thank for the emergence of the global flu pandemic. In the mid-16th century, ducks were introduced to Chinese rice paddies to feed on the insects that were destroying crops. That meant ducks joined another common feature of Chinese farms: pigs. The duck’s unique biology makes it a generous reservoir for a vast number of viruses, while pigs are uncannily efficient at mixing different viruses together into new strains and passing them to humans. Breeding these two animals in proximity quickly led to the combination and transmission of new viral strains. Novel and highly virulent pathogens — hybrid pig-duck influenza strains — then crossed the species barrier and have been tormenting humanity ever since.”