Microbes : Fungi, Protozoa

by National Institute of Health

(Page 2 of 8)

Fungi

A fungus is actually a primitive plant. Fungi can be found in air, in soil, on plants, and in water. Thousands, perhaps millions, of different types of fungi exist on Earth. The most familiar ones to us are mushrooms, yeast, mold, and mildew. Some live in the human body, usually without causing illness. Fungal diseases are called mycoses.

Mycoses can affect your skin, nails, body hair, internal organs such as your lungs, and body systems such as your nervous system. Aspergillus fumigatus, for example, can cause aspergillosis, a fungal infection in your respiratory system.

Some fungi have made our lives easier. Penicillin and other antibiotics, which kill harmful bacteria in our bodies, are made from fungi. Other fungi, such as certain yeasts, also can be helpful. For example, when a warm liquid, such as water, and a food source are added to certain yeasts, the fungus ferments. The process of fermentation is essential for making healthy foods like some breads and cheeses.

Protozoa

Protozoa are a group of microscopic one-celled animals. Protozoa can be parasites or predators. In humans, protozoa usually cause disease.

Some protozoa, like plankton, live in water environments and serve as food for marine animals, such as some kinds of whales. Protozoa also can be found on land in decaying matter and in soil, but they must have a moist environment to survive. Termites wouldn't be able to do such a good job of digesting wood without these microorganisms in their guts.

Malaria is caused by a protozoan parasite. Another protozoan parasite, Toxoplasma gondii, causes toxoplasmosis in humans. This is an especially troublesome infection in pregnant women because of its effects on the fetus, and in people with HIV infection or other immune deficiency disorder.

Microbes Have Bothered Us for Millennia

Microbes have probably always caused infections and diseases in humans. Since ancient times, historians have documented some of those diseases. Present-day archeologists and microbiologists (scientists who study microbes) are discovering evidence of infectious disease in prehistoric human skeletons.

In a fascinating find in the late 20th century, researchers uncovered evidence that prehistoric humans were troubled by microbial parasites and used natural remedies against them. Along with the frozen mummy of the "Ice Man," who was found in the mountains of northern Italy and lived between 3300 and 3100 B.C., scientists found a type of tree fungus containing oils that are toxic to intestinal parasites. Later, in the laboratory, researchers found the eggs of a microscopic parasitic intestinal roundworm, Trichuria trichiura (whipworm), in his intestines.

Smallpox, which is caused by a variola virus, was described in ancient Egyptian and Chinese writings. According to some researchers, over the centuries smallpox was responsible for more deaths than all other infectious diseases combined. It killed millions of people over thousands of years before being eradicated late in the 20th century by worldwide vaccination. The last case of naturally occurring smallpox was recorded in 1977.

The protozoan parasite Plasmodium causes malaria, a tropical disease that usually is transmitted to humans during the bite of the Anopheles mosquito. In ancient times, this disease was mentioned in Egyptian writings, called hieroglyphics, and was described in detail by the Greek physician Hippocrates. Malaria ravaged invaders from the Roman Empire. Though rare in the United States, malaria remains a serious public health threat worldwide.

Evidence on a 1300 B.C. Egyptian stone engraving shows that poliomyelitis (polio) also has been around since ancient times. In the 1990s, public health officials launched a massive international vaccination campaign to eradicate the polio virus, which causes paralysis and can be deadly.

In the 14th century, a bacterium that modern scientists identified as Yersinia pestis caused the bubonic plague, or Black Death. Bubonic plague entered Europe and Africa through infected rodents and fleas that accompanied travelers along trade routes from Mongolia. The plague epidemic spread through Europe, Africa, and the Middle East, killing about 20 million people in Europe alone. Plague is spread to humans through the bites of fleas, which pick up the bacteria while sucking blood from rodents, especially rats. In the United States, health care providers report cases of plague even today, most of which are found in the Southwest.

Viruses caused two major pandemics during the 20th century. From 1918 to 1919, the influenza virus ravaged worldwide populations. Estimates of the number of people killed during the so-called "Spanish flu" pandemic range from 20 million to 40 million. HIV, which was identified in 1984, killed an estimated 3.1 million people worldwide in 2005 alone.

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.