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You are here: Home Hiking Information Water Water Pathogens

Water Pathogens

Giardia & Cryptosporidium

Giardo and Crypto

Giardia Cyst, Cryptosporidium oocysts left and right respectively. 
Image provided by the CDC


The larger disease causing contaminants are living organisms classified as parasites.  Giardia and Cryptosporidium are the most common parasites found in water in the United States and are greater than a micron in size (10^-6 m).  The number of people infected  each year in the United States with Giardia or Cryptospridium is estimated in the millions.

A person can get Giardia or Cryptospridiosis with the digestion as few as 10 to 30 cysts.  Once infected a person can shed 10 billion cysts in their stool in one day and continue to shed cysts for weeks and sometimes months.  Animals with Giardia or Cryptospridiosis can shed far more cysts.  A six day old calf can shed 40 billion Giardia cysts in one day.  These cysts can stay dormant for months which increases the chances of spreading the microscopic parasite.

Symptoms of Giardia or Cryptospridiosis typically begin seven days after becoming infected.  Symptoms from Giardia include; diarrhea, flatulence, greasy stools, stomach cramps and upset stomachs.  Giardia symptoms typically last 3 to 6 weeks.  Cryptospridiosis symptoms include stomach cramps, dehydration, Nauseau, fever and weight loss.  Symptoms for Cryptospridiosis typically last 1 to 2 weeks.

Water with Giardia and Cryptospridiosis can be treated with chemicals (purified), filtered, or boiled.  To treat the water by boiling the Center for Disease Control and Prevention recommends boiling the water for 1 minute and continuing the boil for 3 minutes for every 3000 feet in elevation.  The boiling method is not practical for most hikers because of the time and fuel requirements.  Chemicals added to the water can kill the parasites if the directions are followed correctly.  Filters with an absolute pore size of less than 1 micron can filter out the Giardia and Cryptospridiosis oocysts.  Always verify the pore size and use your water filter according to the manufacturers guidelines.





Salmonella CDC

Salmonella, Photo by Janice Haney Carr, CDC

Bacteria such as Salmonella and Escherichia coli (E. coli) may also be found in drinking water.  These bacteria are small, typically less than 1 micron.  The water is typically contaminated with bacteria from feces from an infected human or animals.

Symptoms for salmonellosis include diarrhea, fever, and abdominal cramps and develop 12 to 72 hours after being infected.  Most healthy adults recover without medical treatment.  People with severe diarrhea may need to be hospitalized and require antibiotics.

Symptoms from E. coli vary, some strains are harmless while others cause illness. Symptoms may include diarrhea, urinary tract infection, and resperatory illness.  For most cases non-specific supportive therapy and hydration is the recommended treatment.





Norovirus by CDC

Norovirus, Photo by Charles D. Humphrey, CDC

Viruses such as enterovirus , norovirus and rotavirus can also be found in drinking water.  Viruses are typically too small (< 0.1 micron) to filter so another treatment would be necessary to effectively treat water with viruses.

Non-polio enteroviruses is common and infects an estimated 10 million people annually in the United States.  Most people infected do not show any symptoms.  However some may show mild respiratory symptoms and a flu-like illness.

Norovirus is a virus that causes gastroenteritis or stomach flu symptoms.  The symptoms typically include nausea, vomiting, diarrhea, and stomach cramps.  Most people recover in 1-2 days but can still infect others for up to two weeks after recovery.

Rotovirus is the most common cause of gastroenteritis in young children and infants.  The virus causes vomiting and diarrhea for 3 to 8 days.  For healthy people the rotovirus is a self limited illness and lasts just a few days.

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