Giardiasis and Cryptosporidiasis Transmissable To Humans
This information was in part summarized from Health Canada (December 2013)
General Information
  • Giardia and Cryptosporidium are microscopic, protozoan parasites that can be found in water contaminated with the feces of infected animals.
  • Giardia is often found in human, beaver (Castor canadensis), muskrat (Ondatra zibethicus), and dog feces. Cattle feces appear to be the primary source of Cryptosporidium, although these parasites have also been found in humans and other animals. Drinking water sources become contaminated when feces containing the parasites are deposited or flushed into water.
  • In humans, Giardia causes an intestinal illness called giardiasis or "beaver fever". Cryptosporidium is responsible for a similar illness called cryptosporidiosis.
  • Giardia and Cryptosporidium parasites produce cysts that are very resistant to harsh environmental conditions. When ingested, they germinate, reproduce, and cause illness. After feeding, the parasites form new cysts, which are then passed in the feces. Studies have shown that ingestion of only a few cysts will cause illness in humans.
Life Cycle of Giardia
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Giardia Life Cycle
Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the feces (diagnostic stages) . The cysts are hardy and can survive several months in cold water. Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral route (hands or fomites) . In the small intestine, excystation releases trophozoites (each cyst produces two trophozoites) . Trophozoites multiply by longitudinal binary fission, remaining in the lumen of the proximal small bowel where they can be free or attached to the mucosa by a ventral sucking disk . Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in nondiarrheal feces . Because the cysts are infectious when passed in the stool or shortly afterward, person-to-person transmission is possible. While animals are infected with Giardia, their importance as a reservoir is unclear.
Signs and Symptoms
  • Gastrointestinal upset, malaise, and weight loss are the most common symptoms caused by Giardia. Vomiting, chills, headache, and fever may also occur. These symptoms usually surface 6 to 16 days after the initial contact and can continue as long as a month.
  • The symptoms of cryptosporidiosis are similar; the most common include watery diarrhea, abdominal cramps, nausea, and headaches. These symptoms occur within 2 to 25 days of infection and usually last one or two weeks; in some cases they may persist for up to a month.
Treatment and Risk Reduction
  • If water purification is inadequate, drinking water may contain sufficient numbers of parasites to cause illness. Other sources include direct exposure to the feces of infected humans and animals, eating contaminated food, and accidental ingestion of contaminated recreational water. The comparative importance of these various routes of exposure is unknown.
  • Giardia is usually cleared from healthy people without treatment within a month. Anti-parasitic drugs are available and are particularly helpful for immunocompromised people in whom the illness could otherwise develop into a persistent state.
  • Cryptosporidium also will usually disappear from healthy people within a month without treatment. Anti-diarrheal drugs and rehydration therapy may be used if diarrhea becomes severe. No drugs to fight the illness have been approved, although many are currently being tested.
  • Both parasites, but particularly Cryptosporidium, can pose a more serious threat to immunocompromised people, such as those living with AIDS or cancer, or transplant patients receiving immunosuppressive drugs. For these people, the symptoms are more severe and can be life threatening. It is presently unknown whether immunocompromised individuals are at greater risk of contracting giardiasis or cryptosporidiosis than the general public. Nevertheless, immunocompromised individuals should discuss these risks with their physicians.
  • People who wish to take extra precautions can boil their water for one minute to kill any parasites that may be present. This practice will also destroy any other microorganisms that might be of concern to these individuals. As bottled water is not routinely monitored for Giardia and Cryptosporidium, its suitability as an alternative to boiled tap water is unknown.
  • If you are suffering from diarrhea and suspect that your symptoms may be due to Giardia or Cryptosporidium, visit your physician and mention any exposure you may have had to water, food, or feces that could have been contaminated by the parasites.
Further Reading
Return to Manual Home Page Disease List - Body Region Affected Disease List - Causative Agent or Risk Factor Disease Surveillance Form Glossary Contact Information
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