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.

Drugs that treat chronic conditions and lifestyle ailments are more profitable. Modern medicine needs new kinds of antibiotics to treat drug-resistant infections, but antibiotic research and development are expensive, risky, and time-consuming.

About 36,000 people die from flu-related complications each year in the United States. More than 200,000 are hospitalized.

About 36,000 people die from flu-related complications each year in the United States. More than 200,000 are hospitalized.

All of the above are urgently needed in developing nations. A major barrier to achieving these improvements is the underlying weakness of health systems in resource-poor countries, including a shortage of health workers and a lack of disease surveillance programs.

All of the above are urgently needed in developing nations. A major barrier to achieving these improvements is the underlying weakness of health systems in resource-poor countries, including a shortage of health workers and a lack of disease surveillance programs.

All of the above are urgently needed in developing nations. A major barrier to achieving these improvements is the underlying weakness of health systems in resource-poor countries, including a shortage of health workers and a lack of disease surveillance programs.

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.

Antibiotics only work on bacterial infections, not viral infections such as influenza and the common cold. In fact, inappropriate use and overuse of antibiotics contributes to the emergence of drug-resistant bacteria. 

All are examples of ways that pathogens can spread. Coughing is an example of airborne droplet transmission; eating undercooked pork is an example of common vehicle transmission; a flea bite is an example of vector transmission; and breathing contaminated dust particles is an example of airborne transmission.

All are examples of ways that pathogens can spread. Coughing is an example of airborne droplet transmission; eating undercooked pork is an example of common vehicle transmission; a flea bite is an example of vector transmission; and breathing contaminated dust particles is an example of airborne transmission.

All are examples of ways that pathogens can spread. Coughing is an example of airborne droplet transmission; eating undercooked pork is an example of common vehicle transmission; a flea bite is an example of vector transmission; and breathing contaminated dust particles is an example of airborne transmission.

All are examples of ways that pathogens can spread. Coughing is an example of airborne droplet transmission; eating undercooked pork is an example of common vehicle transmission; a flea bite is an example of vector transmission; and breathing contaminated dust particles is an example of airborne transmission.

Tuberculosis is caused by a bacterial infection. Chicken pox, the common cold, and influenza are all caused by viral infections.

Tuberculosis is caused by a bacterial infection. Chicken pox, the common cold, and influenza are all caused by viral infections.

Tuberculosis is caused by a bacterial infection. Chicken pox, the common cold, and influenza are all caused by viral infections.

Although there are treatments available in the form of antivirals, we still currently lack a vaccine for HIV.

Although there are treatments available in the form of antivirals, we still currently lack a vaccine for HIV.

Although there are treatments available in the form of antivirals, we still currently lack a vaccine for HIV.