1. The new coronavirus
The 2019 novel coronavirus (2019-nCoV) is a new strain of coronavirus that first appeared in Wuhan, China, in December 2019. Though it was only just discovered, 2019-nCoV has already spread rapidly in China and around the world. As of Feb. 10, 2020, the virus has led to more than 40,000 illnesses and 900 deaths in China, as well as more than 400 illnesses and two deaths outside of mainland China. (The vast majority of cases and deaths have occurred in Hubei Province, where Wuhan is located.)
Coronaviruses are a large family of viruses that cause respiratory illnesses. This family includes the viruses that cause SARS (severe acute respiratory syndrome) and MERS (Middle East respiratory syndrome).
Because 2019-nCoV is so new, many unknowns remain about the virus, including exactly how easily it spreads, how deadly it is and whether it will cause a global pandemic. (The World Health Organization has declared the 2019-nCoV outbreak a “public health emergency of international concern,” but has not yet declared it a pandemic.)
Studies suggest 2019-nCoV likely originated in bats, but made it’s “jump” to people through a yet-to-be-identified animal, which acted as a bridge between bats and humans.
2. Smallpox
Scientists think that smallpox, which causes skin lesions, emerged about 3,000 years ago in India or Egypt, before sweeping across the globe. The Variola virus, which causes smallpox, killed as many as a third of those it infected and left others scarred and blinded, according to the World Health Organization.
A photo taken in 1975 shows the village cemetery in the Bangladesh countryside where smallpox victims were buried. The disease is believed to have killed 46 percent of its victims at a hospital in the Dacca, Bangladesh, ravaging the country for centuries.
In 1980, the WHO declared the disease officially eradicated, after a decade-long vaccination campaign. The last remaining samples of the virus are being held in facilities in the United States and Russia.