1-2 Microbes have a large impact on human health

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• Microbes cause many infectious diseases.
• Vaccines, antibiotics, and many other advances have lessened the impact of infectious disease in the developed world, but infectious disease in developing countries is high.
• New illnesses caused by microorganisms continue to emerge and known pathogens are becoming resistant to treatment.

If you ask the average person how microbes (or germs) impact their lives, they would immediately think of disease. This is not a silly view, as Figure 1-16 shows a number of important pathogens.

While death from infectious disease in the U.S. has been greatly diminished, infection rates in developing nations remain unacceptably high. "Ancient" diseases continue to be a problem where nutrition and sanitation are poor, and emerging diseases such as Acquired Immunodeficiency Syndrome (AIDS) are even more dangerous for such populations. The Centers for Disease Control and Prevention (the U.S. government agency charged with protecting human health and safety) estimate that about 9% of adults between the ages of 18-49 in Sub-Saharan Africa are infected with HIV. Yet as you can see in Figure 1-13, AIDS is only one of a number of new diseases that have emerged. Many of the new diseases are viral in nature, making them notoriously difficult to treat and they have no known cure. Influenza and pneumonia are leading killers of the elderly even in the U. S. and other developed nations. Even the common cold causes illness and misery for almost everyone and drains the productivity of all nations.

Disease due to food-borne pathogens also remain a problem, largely because of consumption of improperly processed or stored foods. Understanding the sources of contamination and developing ways to limit the growth of pathogens in food is the job of food microbiologists.

Surprisingly, many diseases that were previously thought to have only behavioral or genetic components have been found to involve microorganisms. The clearest case is that of ulcers, which was long thought to be caused by stress and poor diet. However the causative agent is actually a bacterium, Helicobacter pylori, and many ulcers can be cured with appropriate antibiotics. Work on other non-infectious diseases such as heart disease, stroke and some autoimmune diseases also suggest a microbial component that triggers the illness.

Finally, some pathogenic microbes that had been "controlled" through the use of antibiotics are beginning to develop drug resistance and therefore reemerge as serious threats in the industrialized world as well as developing nations. Tuberculosis is an illness that was on the decline until the middle 80's. It has recently become more of a problem, partly due to drug resistance and partly due to a higher population of immunosuppressed individuals from the AIDS epidemic. Staphylococcus aureus strains are emerging that are resistant to many of the antibiotics that were previously effective against them. These staph infections are of great concern in hospital settings around the world. Understanding both familiar killers and new pathogens will require an understanding of their biology, and thus an understanding of the field of microbiology.

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