Microbes: Infections

by National Institute of Health

(Page 4 of 8)

You Can Get Microbes from Tiny Critters

Mosquitoes may be the most common insect carriers, also called vectors, of pathogens. Anopheles mosquitoes can pick up Plasmodium, which causes malaria, from the blood of an infected person and transmit the protozoan to an uninfected person.

Fleas that pick up Yersinia pestis bacteria from rodents can then transmit plague to humans.

Ticks, which are more closely related to crabs than to insects, are another common vector. The tiny deer tick can infect humans with Borrelia burgdorferi, the bacterium that causes Lyme disease, which the tick picks up from mice.

Some Microbes in Food or Water Could Make You Sick

Every year, millions of people worldwide become ill from eating contaminated foods. Although many cases of foodborne illness or "food poisoning" are not reported, the Centers for Disease Control and Prevention (CDC) estimates there are 76 million cases of such illnesses in the United States each year. In addition, CDC estimates 325,000 hospitalizations and 5,000 deaths are related to foodborne diseases each year. Microbes can cause these illnesses, some of which can be fatal if not treated properly.

Poor manufacturing processes or poor food preparation can allow microbes to grow in food and subsequently infect you. Escherichia coli (E. coli) bacteria sometimes persist in food products such as undercooked hamburgemeat and unpasteurized fruit juice. These bacteria can have deadly consequences in vulnerable people, especially children and the elderly.

Cryptosporidia are bacteria found in human and animal feces. These bacteria can get into lake, river, and ocean water from sewage spills, animal waste, and water runoff. Millions can be released from infectious fecal matter. People who drink, swim in, or play in infected water can get sick. People, including babies, with diarrhea caused by Cryptosporidia or other diarrhea-causing microbes such as Giardia and Salmonella, can infect others while using swimming pools, waterparks, hot tubs, and spas.

Transplanted Animal Organs May Harbor Germs

Researchers are investigating the possibility of transplanting animal organs, such as pig hearts, into people. They, however, must guard against the risk that those organs also may transmit microbes that were harmless to the animal into humans, where they may cause disease.r

Some People Are Immune to Certain Diseases

We become immune to germs through natural and artificial means. As long ago as the 5th century B.C., Greek doctors noticed that people who had recovered from the plague would never get it again - they seemed to have become immune or resistant to the germ. You can become immune, or develop immunity, to a microbe in several ways. The first time T cells and B cells in your immune system meet up with an antigen, such as a virus or bacterium, they prepare the immune system to destroy the antigen. Because the immune system often can remember its enemies, those cells become active if they meet that particular antigen again. This is called naturally acquired immunity.

Another example of naturally acquired immunity occurs when a pregnant woman passes antibodies to her unborn baby. Babies are born with weak immune responses, but they are protected from some diseases for their first few months of life by antibodies received from their mothers before birth. Babies who are nursed also receive antibodies from breast milk that help protect their digestive tracts.

Artificial immunity can come from vaccines. Immunization with vaccines is a safe way to get protection from germs. Some vaccines contain microorganisms or parts of microorganisms that have been weakened or killed. If you get this type of vaccine, those microorganisms (or their parts) will start your body's immune response, which will demolish the foreign invader but not make you sick. This is a type of artificially acquired immunity.

Immunity can be strong or weak and short- or long-lived, depending on the type of antigen, the amount of antigen, and the route by which it enters your body. When faced with the same antigen, some people's immune system will respond forcefully, others feebly, and some not at all.

The genes you inherit also can influence your likelihood of getting a disease. In simple terms, the genes you get from your parents can influence how your body reacts to certain microbes.

Microbes Cause Different Kinds of Infections

Some disease-causing microbes can make you very sick quickly and then not bother you again. Some can last for a long time and continue to damage tissues. Others can last forever, but you won't feel sick anymore, or you will feel sick only once in a while. Most infections caused by microbes fall into three major groups.

• Acute infections
• Chronic infections
• Latent infections

Acute Infections

Acute infections are usually severe and last a short time. They can make you feel very uncomfortable, with signs and symptoms such as tiredness, achiness, coughing, and sneezing. The common cold is such an infection. The signs and symptoms of a cold can last for 2 to 24 days (but usually a week), though it may seem like a lot longer. Once your body's immune system has successfully fought off one of the many different types of rhinoviruses or other viruses that may have caused your cold, the cold doesn't come back. If you get another cold, it's probably because you have been infected with other cold-causing viruses.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.