||National Park Service
US Department of the Interior
|Office of Public Health
||1201 Eye Street, NW
Washington, DC 20005
|Office of Public Health - Giardia Factsheet
|Points Of Contact
|Assistant to Director for Science
|Assistant to Director for Field Operations
|National Capitol Region
|Pacific West Region
Giardia is a microscopic protozoan parasite that infects man and warm-blooded
animals. People become infected when they ingest the cysts of this protozoan
parasite in contaminated water or food. Giardiasis is the most prevalent
water-borne disease in the United States. The parasite is wide spread in the
U.S. including Alaska.
Symptoms of giardiasis typically last for about 2 weeks. They usually include
severe diarrhea, nausea, abdominal cramps, fatigue and weight loss. The onset
of symptoms normally occur within 7-10 days after exposure to the parasite.
Symptoms are more severe in children. Persons with compromised immune systems
including AIDS patients and persons receiving chemo- or radiation therapy are at
Humans and warm blooded domestic and wild animals, particularly beaver and
muskrats, are the reservoir of this parasite. Giardia parasites are excreted in
the feces. The environmentally resistant cysts can last for several months in
water and can even withstand freezing for a short period of time.
The primary sources of this disease are surface waters contaminated by animals
and water supplies contaminated by human sewage.
Large community outbreaks have occurred from drinking treated but unfiltered
water. Smaller outbreaks have resulted from contaminated food and
person-to-person transmission in daycare centers. Giardiasis also is frequently
transmitted by ingesting untreated surface water and water from shallow wells.
Giardiasis is a common disease among hikers and campers who drink untreated
surface water from lakes, streams and springs.
Exposure to this parasite can be minimized by:
- Avoiding ingesting untreated water from lakes, rivers, streams, and shallow
wells (less than 25 foot deep).
- The most certain treatment to destroy Giardia is to bring water to
a rolling boil for one minute (Add an additional minute
for each 1,000 feet above sea level). Boiling will also destroy other
organisms causing waterborne disease.
- A far less reliable treatment is the use of portable water filters combined with disinfection. Some
claim to remove Giardia cysts, but test protocols are not uniform in the industry
and many have not been tested in unbiased laboratories. Purchase only from
reputable dealers, and check product literature to ensure that the filter is
labeled according to filter manufacturing standards as at least an "Absolute" 1 micron filter, or one labeled as
meeting American National Standards Institute (ANSI/NSF) (formerly the National
Sanitation Foundation) International Standard #53 for "Cyst Removal"
followed by disinfection. Add 8 drops of
bleach or 20 drops of tincture of iodine per gallon of water and let stand for 30
minutes. No other filters are
reliable for removing Giardia.
- For short trips, take a supply of water from home or from other treated
domestic sources. Due to the lack of labeling and manufacturing standards,
there is no assurance that bottled water is safer than public drinking water and
may require boiling also.
- Practicing good personal hygiene targeting the need for proper handwashing
before handling food, eating, and after changing diapers, and using the toilet.
If you have any questions, please contact your nearest Regional Point of Contact,
park sanitarian or call WASO Public Health for more information.
Health Information, National Center for Infectious Diseases, Centers for Disease
Control and Prevention, Department of Health and Human Services
Return to Waterborne Infectious Agents Page