Giardiasis (also known as lamblia dysentery or lambliosis) is an infectious diarrheal disease caused by the parasite Giardia lamblia. Giardiasis is the most commonly reported parasitic food- and waterborne disease in Europe (ECDC, 2014-2022; Leitsch, 2015). The disease is still insufficiently recognized and underreported with an estimated incidence 4 to 100 times higher than actual case reports (Huang and White, 2006). Rising temperatures and more extreme events associated with climate change are expected to increase the number of giardiasis cases.

Source & transmission

Giardia lamblia parasites can survive in the small intestine of humans, wild and domestic mammals. Before the microscopic parasites are passed in faeces, they become encased within hard shells called cysts, which allows them to survive for months outside the body in cold water or soil. An infected person can carry Giardia cysts unnoticed and infect other people when hygienic practices are inadequate (Adam, 2001; Huang and White, 2006).

The main sources of infection are contaminated water, food, soil or surfaces. Disease outbreaks often happen after consumption of untreated drinking water or contact with contaminated water sources during recreation. In addition, infections are common in day-care centres or due to unsanitary food preparation practices. Chlorination as water treatment may not kill Giardia cysts, especially when the water is cold (Stuart et al., 2003; Thompson, 2011). In Europe, around 35% of the confirmed cases is travel-associated (ECDC, 2023).

Health effects

Health effects range from asymptomatic to severe chronic diarrhoea. More Giardia cysts in the patient’s body cause more severe infections because the parasites use essential nutrients of its host. Typically, the disease results in abdominal and stomach cramps, nausea, vomiting, and diarrhoea with severe bloating. The diarrhoea is watery or even foamy and symptoms last for several weeks. If the fluid loss is very high, it may lead to dehydration. When untreated, giardiasis can have a very troublesome and prolonged course. Giardiasis is usually not life-threatening, except for individuals who are in poor health, malnourished or with a weak immune system (Carmena, 2010).

Morbidity & mortality

In the EEA member countries (excluding Denmark, France, Italy, Liechtenstein, the Netherlands, Switzerland and Türkiye due to absence of data), in the period 2007-2021:

  • 201,848 confirmed infections
  • Notification rate of 2.5 cases per 100 000 population in 2021
  • Low probability of hospitalisation[1]
  • 8 deaths
  • Stable trend since 2015. There was a decline in the number of cases in 2020, possibly due to Covid-19 restrictions and underreporting. In 2021, the number of cases rose again, significantly above the level of the period 2015-2019.

 (ECDC, 2014-2022; ECDC, 2023)

Distribution across population

  • Age group with the highest disease incidence in Europe: 0 – 4 years old (ECDC, 2014-2022)
  • Groups at risk of severe disease course: children and people with a weakened immune system
  • Groups at higher risk of infection: people living or working in areas of poor sanitation or day-care centres (Huang and White, 2006)

Climate sensitivity

Climatic Suitability

Giardia parasites can survive temperatures down to -4°C. However, the parasites suffer from temperatures above 23° C and pH levels above 7.1 (Thompson, 2011).


In Europe, there is not a very clear seasonal pattern, although a higher number of cases is often reported between August and October (ECDC, 2014-2022).

Climate Change Impact

Giardiasis cases increase with rising temperatures and more extreme events. The parasitic Giardia load is often amplified in animals such as rats or beavers. Intensified and more frequent heavy rainfall events, associated to climate change, have the potential to increase Giardia concentrations in water bodies, hence the infection risk (Rupasinghe et al., 2022). Floods can lead to contamination of natural water sources when Giardia cysts originating from manure wash out from fields. The same can happen when the capacity of sewage systems is exceeded. Droughts on the other hand may increase pathogen concentrations to harmful levels (Semenza and Menne, 2009) or cause low flows causing the Giardia parasite to settle in the mud or the sand (Patz et al., 2000).

Prevention & Treatment


  • Improved sanitary facilities
  • Filtration of drinking and recreational water
  • Proper food and water handling to prevent cross-contamination
  • Awareness raising about disease transmission, personal and public hygiene, and quarantining infected people


  • Rehydration and electrolyte replacement
  • Nitazoxanide drugs


Adam, R. D., 2001, Biology of Giardia lamblia, Clinical Microbiology Reviews 14(3), 447–475.

Carmena, D., 2010, Waterborne transmission of Cryptosporidium and Giardia: detection, surveillance and implications for public health, in: Méndez-Vilas, A. (ed.), Current Research, Technology and Education Topics in Applied Microbiology and Microbial Biotechnology, pp. 3-14.

ECDC, 2014-2022, Annual epidemiological reports for 2012-2019 – Giardiasis (lambliasis). Available at Last accessed August 2023.

ECDC, 2023, Surveillance Atlas of Infectious Diseases. Available at Last accessed August 2023.

Huang, D. B., and White, A. C., 2006, An Updated Review on Cryptosporidium and Giardia. Gastroenterology Clinics of North America 35(2), 291–314.

Leitsch, D., 2015, Drug Resistance in the Microaerophilic Parasite Giardia lamblia. Current Tropical Medicine Reports 2(3), 128–135.

Patz, J. A., et al., 2000, Effects of environmental change on emerging parasitic diseases. International Journal for Parasitology 30(12–13), 1395–1405.

Rupasinghe, R., et al., 2022, Climate change and zoonoses: A review of the current status, knowledge gaps, and future trends, Acta Tropica 226, 106225.

Semenza, J. C., and Menne, B., 2009, Climate change and infectious diseases in Europe, The Lancet Infectious Diseases 9(6), 365–375.

Stuart, J. M., et al., 2003, Risk factors for sporadic giardiasis: A case-control study in southwestern England, Emerging Infectious Diseases 9(2), 229–233.

Thompson, R. C. A., 2011, Giardia infections, in: Palmer, S.R. et al. (Eds), Oxford Textbook of Zoonoses: Biology, Clinal Practice, and Public Health, 2nd Edition, pp. 522-535, Oxford University Press.

[1] Hospitalisation probability is labeled as low, moderate or high when respectively < 25%, 25-75% or > 75% of cases are hospitalized.

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