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It could take just one cough, one kiss, one touch or even one bite to change not only your life, but the lives of everyone around you -- and for months or even years. In most cases, the closer those people are to you, the greater the risk. But it isn't always that simple. The risk at hand: an infectious outbreak. (Senthilingam, 4/5)

It is a slow and cumbersome descent hindered by head-to-toe protective suits. A wooden ladder dips down the side, as two researchers in white suits and respirators make their way into Grootboom cave in South Africa. The suits make the journey more cumbersome, but they are the only things standing between safety and exposure. (Bresnahan, 4/6)

This year, the United States has recorded 16 cases of plague, while recent figures have revealed that in the UK, cases of "19th-century" diseases such as scurvy and scarlet fever are on the rise. Changes to our living conditions and the development of medicines have affected the rise and fall of diseases, but they seldom disappear. To date, smallpox remains the only disease to have ever been eradicated. (Eastaugh and Senthilingam, 4/6)

When a researcher's scrawling of the letter O was misinterpreted as a zero in reference to a HIV patient in the early 1980s, the provocative term "patient zero" was born. It triggered a wave of events in which the patient, Gaëtan Dugas, a French-Canadian flight attendant, was erroneously blamed for bringing the human immunodeficiency virus, or HIV, to the United States. (Howard, 4/6)