Giardia lamblia is a microscopic parasite responsible for a diarrheal illness called giardiasis. This single-celled organism resides in the intestines of infected humans and animals. Giardiasis is a common cause of waterborne disease in the United States and a globally prevalent intestinal infection.
How the Parasite Spreads
The Giardia lamblia parasite spreads through the fecal-oral route, meaning that microscopic cysts from the feces of an infected person or animal are ingested by another individual. These cysts are hardy and can survive outside a host for weeks or even months. Contaminated water is a primary source of transmission, including untreated drinking water from lakes, streams, and wells, as well as recreational water sources like swimming pools, hot tubs, and water parks.
Food can also become contaminated with Giardia cysts if it is handled by an infected person with poor hygiene or if it comes into contact with contaminated water. Raw produce, in particular, may carry the parasite if washed with contaminated water. Person-to-person transmission is common in settings such as childcare facilities, where diaper changes and inadequate handwashing can facilitate spread.
Signs and Diagnosis of Infection
Symptoms of giardiasis vary; some people have no symptoms, while others develop severe illness. When symptoms appear, they begin 1 to 3 weeks after exposure. Common signs include watery or greasy diarrhea that may be foul-smelling, abdominal cramps, gas, and nausea. Other symptoms can include fatigue, weight loss, and dehydration. The illness can last for several weeks if untreated, and some individuals may experience recurring symptoms or develop chronic giardiasis.
Diagnosing giardiasis primarily involves laboratory tests of stool samples. Healthcare providers often request multiple samples collected over several days to increase the likelihood of detecting the parasite, as cyst shedding can be intermittent. Technicians examine these samples under a microscope to identify Giardia cysts or trophozoites. Antigen detection tests, which look for specific proteins produced by the parasite in stool, are also commonly used for diagnosis due to their higher sensitivity and quicker results.
Treatment and Prevention
Treatment for giardiasis involves prescription medications. Common medications include metronidazole, tinidazole, and nitazoxanide. The specific medication and dosage depend on the patient’s age, weight, and overall health.
Supportive care, such as staying hydrated, is important for managing symptoms, especially with significant diarrhea. For young children or those with severe dehydration, oral rehydration solutions may be recommended to replace lost electrolytes.
Preventing Giardia infection relies on good hygiene and safe water and food sources. Boiling water is an effective method for killing Giardia cysts, particularly when water quality is questionable, such as during outdoor activities or in areas with unsafe municipal water. Using water filters certified to remove cysts can also provide protection.
Chemical disinfection with iodine or chlorine tablets can be used as an alternative, though their effectiveness against Giardia cysts may vary depending on water temperature and contact time. Practicing thorough hand hygiene, especially after using the restroom, changing diapers, or before preparing food, significantly reduces the risk of person-to-person transmission. Avoiding swallowing water while swimming in lakes, rivers, or pools, and washing fruits and vegetables with safe water, further minimizes exposure to the parasite.