Alan Huffman

Right up until the late 18th century, when the first weighted lines were used to probe the ocean depths, many people believed the seas were bottomless - the watery equivalent of infinite outer space.

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.

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