Pathogens and Other Microorganisms

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The USGS works to monitor and assess how disease-causing pathogens enter our water and help those who manage drinking and wastewater facilities prevent and treat these viruses, bacteria, algal toxins, and other microorganisms.


Geneticist in lab using a pipette to extract a sample from a centrifuge tube

A USGS geneticist tests samples for presence of certain pathogens. (Credit: Karen Courtot)

Microorganisms are found everywhere in our environment. They are common in the air, soil, water and in the habitats of our daily lives. The vast majority of microorganisms do not cause disease. Instead, they maintain the fertility of soil, they degrade wastes in our landfills and compost piles, and cleanse water of the pollutants we add. We purposefully use some microorganisms to make food (like in cheese, beer, and sauerkraut), we put microorganisms to work in sewage treatment plants, and we use them in biotechnology to produce chemicals.

Although some are beneficial, a few microorganisms called pathogens can make animals and humans sick. In order to cause disease, a pathogen must successfully invade some part of the body and either produce more of itself or produce a chemical (usually called a toxin) which interferes with normal body processes. Whether or not a pathogen is successful in causing disease depends on the health of the individual and the state of his or her immune system, as well as to the number of pathogen cells required to make the person ill. Some pathogens can cause disease when only a few cells are present. In other cases, many cells are required to make a person ill. Children and elderly persons are more susceptible to many pathogens than are young or middle-aged adults.

Waterborne pathogens include disease-causing algal toxins, bacteria, viruses, and protozoans that are transmitted to people when they consume untreated or inadequately treated water. Two such protozoans often seen in the news are Giardia and Cryptosporidium. Their consumption can lead to severe problems of the digestive system, which can be life-threatening to the very young, very old, or those with damaged immune systems. 

Many communities routinely monitor streams, lakes, and beaches for bacteria that indicate a human health threat.



The USGS studies and monitors surface water and groundwater for a variety of pollutants, such as pathogens (viruses, bacteria, and protozoan). Here are a few links to demonstrate why USGS does what it does.



Centers for Disease Control and Prevention

National Center for Biotechnology Information