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Biology LibreTexts

15.19C: Giardiasis

  • Page ID
    12314
  • Giardiasis, sometimes referred to as beaver fever, is caused by the protozoan Giardia lamblia and results in diarrheal illness.

    Learning Objectives

    • Summarize the life cycle and route of transmission for Giardia lamblia

    Key Points

    • Giardia lamblia is transmitted by exposure or ingestion of fecal contaminated sources such as soil, food, and water.
    • Giardiasis is a common worldwide cause of gastroenteritis.
    • The structure and life cycle of Giardia lamblia allow for survival in harsh environments and resistance against numerous types of disinfectants.

    Key Terms

    • giardiasis: an infectious diarrheal disease caused by the Giardia lamblia parasite
    • zoonotic: of or relating to zoonosis, the transmission of an infectious disease between species.
    • hematuria: The presence of blood in the urine.

    Giardiasis is a protozoan disease caused by Giardia lamblia. Giardiasis, referred to as beaver fever, is a common cause of gastroenteritis worldwide. The protozoa, Giardia lamblia, also referred to as Giardia intestinalis or Giardia duodenalis, infects humans via the fecal-oral route and is also suspected to be zoonotic. The organism is commonly found in soil, food, or water that has been contaminated with fecal matter from infected humans or animals. Beavers typically spread the parasite in their fecal matter in rivers and streams hence, giardiasis is commonly referred to as beaver fever. Individuals susceptible to infection by Giardia lamblia are those who come in frequent contact with individuals already infected. Travelers that spend time in wilderness area are at an increased risk due to ingestion of contaminated food or water sources and a lack of medical care or supplies.

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    Figure: Giardia infecting a small intestine: A scanning electron micrograph of the surface of the small intestine of a gerbil infested with Giardia sp. protozoal, present in the trophozoite stage.

    The life cycle, structure, and organization of Giardia lamblia promotes its survival for long periods of time outside the body. The organism itself is protected by an outer shell that provides protection against numerous harsh environments. In addition, the shell provides protection against disinfectants including chlorine. The cysts and trophozoites, found in the fecal matter, are extremely resistant to harsh environments. It is the cysts that are ingested and passed from exposure to contaminated food, water, or by the fecal-oral route. Once in the host, the trophozoites multiply via binary fission. They can either remain free within the lumen or attach to the mucosa by a sucking disk. Once the parasites move towards the colon, the encystation phase occurs and the cysts are infectious when passed in the stool.

    Giardiasis is characterized as a disease of the gastrointestinal system. The symptoms include from fever, diarrhea, hematuria, stomach cramping, vomiting, flatulence, and loose stool. The symptoms are typically present one to two weeks post infection and can disappear and reappear cyclically. The pathogenecity of Giardia lamblia is characterized by its ability to coat the inside of the intestinal wall and inhibit nutrient absorption. The ability of the protozoan to block nutrient absorption can result in vitamin B12 deficiency. Additionally, a development of lactose intolerance is often associated with giardiasis infection.