Tiny microbes, such as viruses, bacteria, fungi and protozoa, can cause infectious diseases in humans. While many microbes do not harm us and some even help us, the disease-causing microbes that we refer to as "germs" can make us sick and can even be deadly
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. Microbes are spread through food, water, the air, the environment, or physical contact between two people or sometimes contact with animals
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The Immune Response and Germ Theory
When our bodies are infected with a microbe our immune system recognizes the foreign invader and launches an immune response
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. The main defense we have against foreign substances such as bacteria or viruses are our white blood cells. White blood cells are produced in the bone marrow and we make about a billion of them each day
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. White blood cells, called macrophages, will detect and destroy bacteria when they see them. When a viral infection begins our T and B-lymphocytes will work to fight off the infection
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. B-cells are important in producing antibodies, which bind to viruses to stop them from replicating and tag them so that other cells can recognize them. Once an infection is cleared, some specialized B and T-cells stay in our bodies and act as memory cells that will easily recognize a virus if we come in contact with it again
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. Scientists have been able to use this idea of acquired immunity and resistance with memory cells to create vaccines, which will be discussed later in this section.
Before the discovery of these disease-causing microbes, people blamed sickness on evil spirits or "bad blood"
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. It wasn't until the invention of the microscope that scientists were able to see microbes and began to study bacteria, viruses, protozoa and fungi. Louis Pasteur was the first scientist to establish the presence of germs by linking them to illnesses. Pasteur proved that fungi and bacteria were present in the air and that they caused sickness in humans
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. He was able to show that germs caused diseases and began to pioneer a way to get rid of them with a process called pasteurization; eventually he was able to develop vaccines for chicken pox, cholera, diphtheria, anthrax and rabies
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. Pasteurization is the process of heating and then cooling a liquid food to remove microbes that may spoil that food (beer, wine, milk, etc.). Pasteur began by studying alcohol fermentation and observed that wine would go sour and turned to vinegar unexpectedly
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. Using a microscope, Pasteur was able to see that small, rod-like microbes were present during fermentation and cause the contaminating the wine
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. Pasteur was able to identify microbes that were responsible for contaminating beer, wine and milk and found that if he heated the liquids to a high temperature and then cooled them down he could kill the microbes and sterilize the liquids
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. This process became known as pasteurization, and was coined to honor Louis Pasteur and his discovery. The identification of microbes that "spoiled" beer and wine led scientists to the understanding that diseases are caused by microorganisms that entered the body; similar to how microbes could contaminate the liquids Pasteur studied
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. Today, scientists are still researching causes of various human diseases and ways to prevent or cure them.
Treatment and Prevention
Two of the most important tools for curing or preventing diseases are antibiotics and vaccines. Antibiotics are a class of drugs that kill bacteria in the human body
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. Antibiotics are targeted at bacterial infections and come in the form of pills, liquids, injections, lotions, or creams; each type is used to attack a specific bacterial pathogen
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Vaccines are another way to fight infectious diseases, but unlike antibiotics that are used to treat an infection, vaccines are used to prevent disease. Vaccines stimulate the immune system by creating antibodies to fight specific infections. A vaccine usually contains a killed or weakened form of a microbe that causes a disease and your body is able to produce antibodies to kill that germ without getting sick
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. When a person who has been given a vaccine is later exposed to the illness, their body is already prepared to fight the infection because of the antibodies that are already created. Edward Jenner developed the first real vaccine when he inoculated a young boy with the cowpox virus in 1796
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. Jenner found that people exposed to the cowpox virus did not contract smallpox, a disease that was killing thousands of people. Edward Jenner began by observing patients who had contracted cowpox while working on the farm. These patients had mild discomfort, aching, pustules and swelling but the disease did not lead to death like smallpox
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. Jenner noted that the individuals who were infected with cowpox did not become infected with smallpox when they were exposed to this. Jenner hypothesized that this was because the individuals who were infected with cowpox had antibodies that made them immune to the smallpox virus. Jenner tested his hypothesis on an 8-year old boy, James Phipps, by vaccinating him with a fluid from pustules of cowpox-infected patients and then exposing him to the smallpox virus
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. When he came in contact with the disease Phipps did not contract smallpox, a result of the immunity he obtained from the cowpox injection. Jenner had successfully created the smallpox vaccination by triggering the immune system to create antibodies for a pathogen that was closely related to smallpox to fight the infection when exposed to it. This discovery would lead to the development of many other vaccines throughout history.
