Giardiasis

Giardiasis is a parasitic disease of humans and other mammals caused by the protist enteropathogen Giardia duodenalis, which is also known as G. lamblia and G. intestinalis. The organism exists in two forms: the infectious cyst form, which survives in the environment and transmits infection, and the trophozoite form, which attaches to the intestinal wall and causes disease. Giardia duodenalis has been classified into eight genetic assemblages designated A through H, with assemblages A and B representing the primary genotypes that infect humans and the widest range of host species.

The clinical presentation of giardiasis varies considerably, ranging from completely asymptomatic infection to severe gastrointestinal illness. The most characteristic symptom is steatorrhea, a type of diarrhea characterized by fatty, greasy, foul-smelling stools that tend to float. Infected individuals commonly experience abdominal pain, weight loss, and weakness resulting from dehydration and malabsorption of nutrients. Less frequent manifestations include skin rash, hives, and joint swelling. Symptoms typically develop within 9 to 15 days after exposure, though onset may occur as early as one day or as late as three weeks. Without treatment, diarrhea may persist for weeks or months, and some infected individuals remain symptom-free even while harboring the infection for extended periods.

Giardiasis is especially common in children and travelers, though infection can occur in any population exposed to the parasite. The disease has a global distribution, with transmission occurring in both developed and developing countries. In the United Kingdom, approximately 75 percent of infections are acquired domestically rather than through international travel. In the United States, giardiasis occurs more frequently during summer months, a pattern attributed to increased outdoor activities and wilderness travel. Various animals serve as reservoirs, including pets, beavers, other rodents, cattle, and sheep, and these animal populations are believed to play a role in maintaining environmental contamination.

Giardiasis is transmitted via the fecal-oral route through the ingestion of Giardia cysts. Primary transmission pathways include person-to-person contact, consumption of contaminated water, and ingestion of contaminated food. Both symptomatic individuals and asymptomatic carriers excrete cysts and contribute to disease spread. The cysts demonstrate considerable environmental persistence, remaining infectious for up to three months in cold water. Infection can be established with ingestion of relatively few cysts, facilitating efficient transmission in settings with inadequate sanitation or hygiene practices.

Populations at elevated risk for giardiasis include children, who may be more susceptible to infection and experience more severe symptoms, and travelers to regions with inadequate water treatment and sanitation infrastructure. In developed countries, factors increasing infection risk include changing diapers, consuming raw or unwashed food, owning dogs, and traveling to developing regions. The disease affects individuals across all age groups, but the clinical impact may be more pronounced in those with compromised nutritional status or immune function.

Prevention of giardiasis centers on proper personal hygiene practices and careful food handling. Effective measures include thorough handwashing with soap and water after using the toilet, changing diapers, and before preparing or consuming food. Food should be cooked thoroughly and sanitized appropriately before eating. Water from potentially contaminated sources should be treated through boiling, filtration, or chemical disinfection. Given the role of animal reservoirs in environmental contamination, proper management of pet feces and prevention of animal access to water sources used for drinking or recreation also contribute to prevention efforts.

Source-backed detail is not yet available.

1. 1 Wikidata. giardiasis.
2. 2 Wikipedia. Giardiasis - Wikipedia.

ICD-10

ICD-11

Total cases

148K

Peak month

2007-09

Coverage

2 reporting countries · 2012-09-14 → 2026-05-09