5. Influenza
A seasonal, respiratory infection, flu is responsible for about 3 million to 5 million cases of severe illness, and about 250,000 to 500,000 deaths a year across the globe, according to the World Health Organization.
Periodically, however, the viral infection becomes much more devastating: A pandemic in 1918 killed about 50 million people worldwide. As became apparent from “swine flu” and “bird flu” scares in recent years, some influenza viruses can jump between species.
6. Tuberculosis
Potentially fatal, tuberculosis or “TB” is caused by the bacterium Mycobacterium tuberculosis, which usually attacks the lungs and causes the signature bloody coughs. In patients suffering from an advanced stage of TB, you can see the effects in a lung X-ray (shown in image). ,
The bacterium does not make everyone it infects sick, and up to one-third of the world’s population currently carries the bacterium without showing symptoms. And among people infected with TB (but not HIV), 5% to 10% become sick or infectious at some time during their lifetimes.