In 2008, more than 33 million people worldwide were infected with HIV (human immunodeficiency virus). In that same year, an estimated 2 million people died from AIDS (acquired immunodeficiency syndrome), the final stage of HIV infection.

In 2008, more than 33 million people worldwide were infected with HIV (human immunodeficiency virus). In that same year, an estimated 2 million people died from AIDS (acquired immunodeficiency syndrome), the final stage of HIV infection.

Our bodies contain at least 10 times more bacterial cells than human cells. 

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. 

Infection occurs when viruses, bacteria, or other microbes enter your body and begin to multiply. Disease follows when the cells in your body are damaged as a result of infection, and signs and symptoms of an illness appear.

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.

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.

The use of thimerosal has been an object of controversy, with some arguing that the substance caused autism in children. However, extensive independent research has presented no convincing evidence of harm associated with the low levels of thimerosal previously present in vaccines.

The clearing and settlement of tropical rainforests has exposed woodcutters, farmers, and ecotourists to new vector-borne diseases.

The gap in life expectancy between the richest and poorest countries now exceeds 40 years.

The gap in life expectancy between the richest and poorest countries now exceeds 40 years.

The gap in life expectancy between the richest and poorest countries now exceeds 40 years.