10. SARS-CoV
This virus that causes severe acute respiratory syndrome, or SARS, first occurred in 2002 in the Guangdong province of southern China, according to the WHO. Initially, SARS-CoV likely emerged in bats, then hopped into nocturnal mammals called civets before finally infecting humans. After triggering an outbreak in China, SARS spread to 26 countries around the world, infecting more than 8,000 people and killing more than 770 in just two years.
The disease causes fever, chills and body aches, and often leads to pneumonia, a severe condition in which the lungs become inflamed and fill with pus. SARS has an estimated mortality rate of 9.6 percent, and it has no approved treatment or vaccine (yet). However, no new cases of SARS have been reported since the early 2000s, according to the CDC.
