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.

Strep throat is a bacterial infection that can be treated with antibiotics. The common cold and influenza are both viral infections, which do not respond to antibiotics. Antivirals may be prescribed instead.

Strep throat is a bacterial infection that can be treated with antibiotics. The common cold and influenza are both viral infections, which do not respond to antibiotics. Antivirals may be prescribed instead.

Strep throat is a bacterial infection that can be treated with antibiotics. The common cold and influenza are both viral infections, which do not respond to antibiotics. Antivirals may be prescribed instead.

Growing evidence does suggest that infections are behind many chronic diseases once thought to be caused by genetic, environmental, or lifestyle factors, including peptic ulcers and cervical, liver, and gastric cancers.

The mosquito is the vector for West Nile virus. The mosquito suffers no ill effects from the virus but transmits it to humans and other warm-blooded creatures (such as crows) when it takes a blood meal. 

The mosquito is the vector for West Nile virus. The mosquito suffers no ill effects from the virus but transmits it to humans and other warm-blooded creatures (such as crows) when it takes a blood meal. 

The mosquito is the vector for West Nile virus. The mosquito suffers no ill effects from the virus but transmits it to humans and other warm-blooded creatures (such as crows) when it takes a blood meal. 

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.

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.

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.

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.

Not all microbes are harmful to humans. In fact, many of them protect us, helping our bodies function properly and competing with harmful organisms in an eternal contest for habitable space in or on our bodies. Although the microorganisms that cause disease often receive more attention, most microorganisms do not cause illness.