Health workers killed chickens in a Hong Kong market in 2014 in an effort to stop the spread of H7N9 flu. It's being watched closely as a virus that might spark a pandemic outbreak. Vincent Yu/AP hide caption
SARS SARS
Stories About
SARS
Each year thousands of people from around the world tour the Gomantong Cave in Borneo. Although scientists have found a potentially dangerous virus in bats that roost in the cave, no one has ever gotten sick from a trip here. Razis Nasri hide caption
The Middle East respiratory syndrome coronavirus, which causes MERS, is one of the microbes that has sparked research controversy. NIAID/CDC hide caption
A transmission electron micrograph shows Middle East respiratory syndrome coronavirus particles (colorized yellow). NIAID hide caption
The coronavirus responsible for Middle East respiratory syndrome (green particles) seen on camel cells in a scanning electron micrograph. NIAID/Colorado State University hide caption
Middle Eastern Respiratory Syndrome virus particles cling to the surface of an infected cell. NIAID/Flickr hide caption
A man wears a protective mask as he carries a bouquet of flowers at Women's College Hospital in Toronto in March 2003, when SARS fears about were widespread. Kevin Frayer/AP hide caption
A rogues gallery of the viruses (left to right) that cause MERS, SARS, and influenza. Niaid; 3D4Medical; Niaid/Science Source hide caption
Cross-word Puzzle Composite by Ryan Kellman/NPR hide caption
Fearful of catching the MERS virus, workers wear masks during a soccer match on April 22 at King Fahad stadium in Riyadh. Fayez Nureldine/AFP/Getty Images hide caption
Saudi men walk to the King Fahad hospital in the city of Hofuf on Sunday. In eastern Saudi Arabia, where outbreaks of the MERS virus have been concentrated, people have resumed their habits of shaking hands and kissing. Fayez Nureldine/AFP/Getty Images hide caption
A railway worker wearing protective clothing to ward off the SARS virus controls a line of travelers as they wait to enter Beijing's West Railway Station Tuesday in 2003. Greg Baker/AP hide caption
Different types of coronaviruses can cause a simple cold or a deadly respiratory illness, such as SARS. BSIP/UIG via Getty Images hide caption