NAME: Giardia lamblia
CHARACTERISTICS: G. lamblia is a flagellated enteric protozoan parasite Footnote 1. There are two stages in the lifecycle, a motile vegetative form (trophozoite) which reside in the small intestine and is responsible for disease manifestations and an infective resistant form (cyst) responsible for transmission. Cysts are oval-shaped thin-walled cyst that is 10 to 20 μm in length, 7-10 μm in width and 0.3-0.5 μm thickness Footnote 1, Footnote 2. Trophozoites resemble a pear or teardrop and measure 9-21 μm in length, 5-15 μm in width and 1-2 μm thickness Footnote 3. The trophozoite is an aerotolerant anaerobe that requires glucose as a source of carbohydrate energy and divides by longitudinal binary fission every 9 to 12 hours Footnote 1. The trophozoite has two anteriorly placed nuclei and also has four pairs of posteriorly directed flagella that aid in locomotion and attachment to intestinal epithelium Footnote 1.
PATHOGENICITY/TOXICITY: The majority of infections are asymptomatic. In symptomatic individuals, patients may experience nausea, chills, low grade fever, epigastric pain and sudden onset of watery diarrhea Footnote 4. Diarrhea is often explosive and presents a foul smell without the presence of blood, gas, bloating, mucus, or cellular exudate Footnote 4. Most infections resolve spontaneously within six weeks Footnote 5. Chronic infections can occur and diarrhea leads to dehydration, malabsorption, weight lost and impaired pancreatic function Footnote 4. Chronic infections can last from months to years Footnote 6. G. lamblia are usually found in the upper small intestine, but can be found in the gall bladder and in biliary drainage Footnote 3.
EPIDEMIOLOGY: Giardia infections occur worldwide Footnote 2, affecting persons of all ages with a peak during the late summer and fall months Footnote 1. The prevalence rate in temperate climates is 2-10% in adults and 25% in children whereas in tropical countries 50-80% of people are carriers Footnote 2. G. lamblia is the most commonly identified intestinal parasite in the US as well as in Canada Footnote 7, Footnote 8. CDC reports approximately 20,000 cases per year in US. According to one report from Ontario, Canada showed an incidence rate of 25.8 cases per 100,000 population between 1990 and 1998 Footnote 8. In developed countries, infection occurs most frequently among children in day care centers, hikers, among members of the same family, between male homosexual partners and immunocompromised individuals Footnote 4, Footnote 9-Footnote 13. Drinking untreated water is a common source of infection and can result in community wide epidemics Footnote 1, Footnote 14.
MODE OF TRANSMISSION: The infectious cysts of G. lamblia are excreted in large numbers in feces of infected persons, and they contaminate hands, drinking water, swimming pool Footnote 17, and food Footnote 2. They can be transmitted by the fecal-oral route, or contaminated food and water Footnote 4. Sexual behaviours that aid in transmission of G. lamblia include oral-anal, genital-anal, and digital anal contact Footnote 5. Contaminated soil and fomites can also contain infective cysts Footnote 6, Footnote 18.
INCUBATION PERIOD: 7 to 14 days Footnote 7, Footnote 8; however, the time from ingestion of the cysts to detection of the cysts may be longer than the incubation period, which can result in the stool sample being negative at the time of the onset of symptoms Footnote 8.
RESERVOIR: Humans (principal reservoir), dogs, cats, beavers, and other animals Footnote 14.
ZOONOSIS: Yes, transmitted to humans from a variety of mammals Footnote 2.
VECTORS: Flies are possible mechanical vectors Footnote 2.
SUSCEPTIBILITY TO DISINFECTANTS: Cysts are relatively resistant to chlorination Footnote 1 but Giardia cysts in water can be inactivated with 4 mg/L of chlorine after 60 min at 5°C, at pH levels 6, 7 and 8 Footnote 20. A chlorine concentration of 8 mg/L will inactivate Giardia cysts at pH 6 and 7 after contact for 10 min, and at pH 8 after 30 min. Also, at 25°C, Giardia cysts will be killed when exposed to 1.5 mg/L of chlorine for 10 min at pH 6 Footnote 20. 6% H2O2 can be used as a surface disinfectant or in disinfection of spills.
PHYSICAL INACTIVATION: Giardia is inactivated by exposure to UV light (10 JM-2) Footnote 21. Cysts are relatively resistant to ozonolysis Footnote 1. Cysts are susceptible to boiling and freezing Footnote 5.
SURVIVAL OUTSIDE HOST: Cysts can survive in cold water for several weeks to months Footnote 1, Footnote 2. At 4۫ ºC Giardia lamblia cysts can survive 11 weeks in water, seven weeks in soil, and one week in cattle feces Footnote 18. They remain infective for a significantly shorter period at warmer temperatures - i.e. 25 ºC Footnote 18. Trophozoites do not survive in the environment Footnote 6.
SURVEILLANCE: Monitor for symptoms. Since the incubation time may be shorter than the period required for detection of the cysts in the stool, giardiasis should not be elimnated as a diagnostic possibility if a single stool specimen is negative at the onset of symptoms. Since Giardia is excreted intermittently, in 50% to 70% of cases, Giardia will be detected from a single stool specimen and in 90% of cases after three specimens Footnote 22. In general, the initial diagnosis is made by identification of trophozoites or cysts in stool specimens, duodenal fluid, or small bowel tissue by direct microscopic examination Footnote 22. Other techniques such as detecting soluble stool antigens using enzyme immunoassay (EIA) or polymerase chain reaction technique are also used Footnote 1, Footnote 2, Footnote 14.
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Dehydration and electrolyte abnormalities should be treated symptomatically Footnote 14. In immunocompetent hosts, infection is self-limited; drug therapy can shorten the duration of symptoms and prevent transmission Footnote 4. Metronidazole, tinidazole, and nitazoxanide are indicated for first line treatment Footnote 23.
LABORATORY-ACQUIRED INFECTIONS: Four cases of laboratory-acquired infections have been reported Footnote 24. One case of giardiasis was reported in a clinical laboratory technologist who processed specimens, many of which were in leaky containers Footnote 24-Footnote 26. The parasite was detected in the person’s stool Footnote 26 and transmission was thought to be airborne Footnote 25.
SPECIAL HAZARDS: None.
RISK GROUP CLASSIFICATION: Risk Group 2.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials and animals Footnote 28.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable Eye protection must be used where there is a known or potential risk of exposure to splashes. Footnote 26, Footnote 28.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities.
SPILLS: Allow aerosols to settle, and, wearing protective clothing, gently cover the spill with paper towels and apply an appropriate disinfectant, starting at the perimeter, and working towards the centre. Allow sufficient contact time before clean up and then repeat Footnote 28, Footnote 29.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism before disposing by autoclave, chemical disinfection, gamma irradiation, or incineration. Footnote 28.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled.Footnote 28.
UPDATED: December 2011
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2011