Without an adequate response, an epidemic can develop into a pandemic, which generally means it has spread to more than one continent.

Without effective human intervention, epidemics and pandemics typically end only when the virus or bacteria has infected every available host and all have either died or become immune to the disease.

Historically, war journalists have embedded themselves with one side, which means the greatest threat comes from the clearly delineated enemy of that side.

The slow pace of trains in the U.S. can be maddening, particularly during delays on rail sidings for an hour or more to enable freight trains - which have the right-of-way - to pass.

Architecture students are generally given theoretical projects, often located at distant locations, and told to come up with a design.

Left to their own devices, epidemic diseases tend to follow the same basic process: A virus or bacteria infects a host, who typically becomes sick and in many cases dies. Along the way, the host infects others.