7. HIV/AIDS
At the end of 2018, about 37.9 million people were living with a Human Immunodeficiency Virus (HIV) infection worldwide, with 25.7 million of those individuals in Africa. About 770,000 people worldwide died from HIV/AIDS in 2018; 49,000 of those deaths were in the Americas, according to the WHO.
While many of the worst offenders on this disease list have a long-standing relationship with humans, HIV is a recent arrival. HIV’s decimating effect on certain immune system cells was first documented in 1981. By destroying part of the immune system, HIV leaves its victims vulnerable to all sorts of opportunistic diseases. It is believed to have emerged from Simian Immunodeficiency Virus (SIV), which infects apes and monkeys.
8. Cholera
Cholera causes acute diarrhea that if left untreated can kill within hours. People catch the disease by eating or drinking substances containing the bacterium Vibrio cholerae. The bacteria tend to contaminate food and water through infected feces. Since it can take 12 hours to 5 days to show symptoms, people can unwittingly spread the disease through their feces. Thanks to improved sanitation, cases of cholera have been rare in industrialized nations for the last 100 years, but worldwide it kills between 21,000 and 143,000 individuals every year, the WHO estimates.
During the 19th century, however, cholera spread from its home in India, causing six pandemics that killed millions of people on all continents, according to the World Health Organization. During a cholera epidemic in Peru in 1992, a hospital waiting room (shown in image) was converted to an emergency cholera ward.
More recently, a cholera outbreak in Haiti, which began after that country’s devastating 2010 earthquake, had sickened more than 810000 people and killed nearly 9,000, according to a report published in 2018 in The Journal of Infectious Diseases.