The Life Cycle of Giardiasis

Giardia, a single-celled protozoan, is diagnosed more often than any other intestinal parasite in public health laboratories in the United States. It infects people, dogs, cats and livestock, among other animals. Symptoms of a giardia infection can last up to six weeks. The infection is found worldwide but is most common in warmer climates and infects children more often than adults.

According to the Centers for Disease Control, giardia is recognized as one of the most common causes of waterborne illness.

Ingestion

• The life cycle of giardia begins when the cysts are ingested by a host. It takes as few as 10 cysts to cause an infection of giardiasis.

Trophozoites

• These cysts, once ingested, release two trophozoites--giardia at the feeding stage of their life cycle--into the small intestines. Some of trophozoites attach to the surface of the intestines and reproduce; others float freely within the intestines.

Reproduction

• The trophozoites begin to reproduce once they are attached to the intestines. Reproduction takes place via binary fission, a type of asexual reproduction through cell division.

Encystment

• At some point, the trophozoites will enter into encystment. During this stage they are inactive. The cyst will be excreted in the stool of the host.

Infection

• Once excreted, these cysts will contaminate soil. The cysts can survive several months of cold weather. If the infected soil then contaminates water, food or the hands of a host, these cysts may be ingested, beginning the life cycle again.

Treatment

• Symptoms of giardia infection include diarrhea, abdominal pain, bloating, nausea, vomiting and fatigue. Symptoms will begin seven to 10 days after infection and in most people, the infection is self-limiting. Treatment for giardia generally involves administration of prescription medications metronidazole for five to 10 days or furazolidone for seven to 10 days. Treatment will end the life cycle of the parasite in its human host.