The 1918 influenza pandemic is estimated to have killed between 50 million and 100 million people worldwide. Many of those deaths were due to the effects of pneumococcal pneumonia, a secondary complication of flu for which no antibiotics existed in 1918.

The 1918 influenza pandemic is estimated to have killed between 50 million and 100 million people worldwide. Many of those deaths were due to the effects of pneumococcal pneumonia, a secondary complication of flu for which no antibiotics existed in 1918.

By identifying pathogens in the animals where they naturally live and monitoring those organisms as they move from animals into people, it may be possible to prevent deadly new infections of animal origin from entering and racing through human populations.

Since the beginning of the 20th century the number of people in the world has more than quadrupled—from 1.6 billion to nearly 7 billion—and world population is expected to rise to well over 9 billion by 2050.

Since the beginning of the 20th century the number of people in the world has more than quadrupled—from 1.6 billion to nearly 7 billion—and world population is expected to rise to well over 9 billion by 2050.

Because strep throat is caused by a bacterium called Streptococcus pyogenes, it is treatable with antibiotics but not antivirals. Currently there is no vaccine available to prevent strep throat.

Because strep throat is caused by a bacterium called Streptococcus pyogenes, it is treatable with antibiotics but not antivirals. Currently there is no vaccine available to prevent strep throat.

Because strep throat is caused by a bacterium called Streptococcus pyogenes, it is treatable with antibiotics but not antivirals. Currently there is no vaccine available to prevent strep throat.

About ten trillion microbes live in the human gastrointestinal tract. They are essential for proper digestion and absorption of nutrients.

About ten trillion microbes live in the human gastrointestinal tract. They are essential for proper digestion and absorption of nutrients.

About ten trillion microbes live in the human gastrointestinal tract. They are essential for proper digestion and absorption of nutrients.

An estimated 1.8 million airline passengers cross international borders daily, creating routes by which human infections can radiate around the world within hours.

An estimated 1.8 million airline passengers cross international borders daily, creating routes by which human infections can radiate around the world within hours.

White blood cells are not a type of infectious agent. Part of the immune system, white blood cells fight infection rather than cause it. 

White blood cells are not a type of infectious agent. Part of the immune system, white blood cells fight infection rather than cause it. 

White blood cells are not a type of infectious agent. Part of the immune system, white blood cells fight infection rather than cause it. 

Viruses reproduce the fastest. Humans produce a new generation every 20 years or so; bacteria do it every 20 to 30 minutes, and viruses even faster.

Viruses reproduce the fastest. Humans produce a new generation every 20 years or so; bacteria do it every 20 to 30 minutes, and viruses even faster.

Trichinosis is not a viral disease. It is caused by a helminth (parasitic worm) found in undercooked meat, not by a virus. 

Trichinosis is not a viral disease. It is caused by a helminth (parasitic worm) found in undercooked meat, not by a virus.