Cryptosporidiosis

Cryptosporidiosis is an infectious diarrheal disease caused by the parasite Cryptosporidium. Poor sanitation and limited access to filtered water, common in low-income countries, lead to higher cryptosporidiosis infection risks. To date, the disease is still underdiagnosed and underreported in many countries, including in Europe despite mandatory surveillance (ECDC, 2017-2021; Pane and Putignani, 2022). Despite a relatively low notification rate in Europe, cryptosporidiosis is an important intestinal disease that requires monitoring and control (ECDC, 2017-2021). An increased infection risk is to be expected with rising temperatures, higher rainfall variability and more extreme events associated with climate change, particularly for (vulnerable) young children in urban areas.

Source & transmission

Several different Cryptosporidium species exist, which can infect humans and/or animals (Xiao and Feng, 2017). The infection happens when the infectious stage of the parasite (oocyst) is accidentally ingested via intake of faecal contaminated water or food, or via close contact with infected animals or humans. Considerably small amounts of the oocysts can already cause an infection. Most human transmissions are water-borne, after contact with contaminated surface or drinking water. Contaminated sources of drinking water or recreational waters (including water slides, swimming pools and lakes) can lead to cryptosporidiosis outbreaks (Ramirez et al., 2004; WHO, 2022). Food-borne transmissions and outbreaks happen when agricultural fields are fertilized with animal faeces, contaminated food is handled unsanitary, ingredients are washed with contaminated water, or via contact of humans with infected animals (most often cattle).

Health effects

Infections in humans occur sometimes without symptoms, but usually cause a typical gastrointestinal illness. Three to 12 days after infection, watery diarrhoea occurs, often accompanied by abdominal cramps, vomiting, mild fever and loss of appetite. These symptoms usually last less than 2 weeks but can persist up to a month in severe cases. More than one-third of the infections are persistent, resulting in relapses after a short period of improvement. In these cases, the Cryptosporidium parasite can even cause damage throughout the entire gastrointestinal tract, which leads to severe pains and potential complications. Nevertheless, eliminating the parasite mostly results in rapid and complete recovery, even in severe cases (Davies and Chalmers, 2009).

Morbidity & mortality

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

64,917 infections
Notification rate of 1.79 confirmed cases per 100 000 population in 2021
Moderate probability of hospitalisation [1]
6 deaths and mortality rate below 0.1%. For people with a weak immune system suffering a severe infection, mortality rates can rise to 50% and are a leading cause of death for young children in developing countries (Chako et al., 2010; Sow et al., 2016).
No clear incidence trend between 2015 and 2019. A decrease in cases was reported in 2020 and 2021.

(ECDC, 2017-2021; ECDC, 2023)

Distribution across population

Age group with the highest disease incidence in Europe: 0 – 4 years old (ECDC, 2017-2021)
Groups at risk of severe disease course: children under 2 years old and people with low immunity (Cabada and White, 2010; Gerace et al., 2019)
Groups at higher risk of infection: people that come in close contact with animal or human faeces, sanitary facilities or unsafe water, including animal handlers, travellers, health- and day-care workers (Putignani and Menichella, 2010).

Climate sensitivity

Climatic Suitability

Cryptosporidium oocysts thrive between 15 and 32 °C. The parasite is not resilient against persistently high temperatures or dry soils. The infective oocysts have hard shells and can survive temperatures as low as -20°C for several days (Fayer and Nerad, 1996). The oocysts can survive long periods under unfavourable environmental conditions outside the body and remain infective for 2 to 6 months in a moist environment. The cells are also resistant to chemical disinfectants used to purify drinking water or chlorination (Gerace et al., 2019; Pane and Putignani, 2022). This means that eliminating the parasites is difficult once a water source is contaminated (Patz et al., 2000).

Seasonality

In temperate climates, cryptosporidiosis is more common in warmer months. Heavy rainfall towards the end of summer has the potential to increase cryptosporidiosis cases (Jagai et al., 2009). In Europe, infections occur year-round with a peak in September, and a smaller increase in number of cases around April-May in certain countries (ECDC, 2017-2021).

Climate Change Impact

In temperate and tropical regions, cryptosporidiosis occurs more frequently with higher temperatures and more rainfall. Extreme weather resulting in floods or droughts can both lead to more Cryptosporidium parasites in water bodies. Heavy rainfall on the one hand causes water to exceed the capacity of water treatment plants or sewage systems, due to which Cryptosporidium parasite may contaminate various water sources, including drinking water and recreational waters. Infection risks due to increased frequency and intensity of extreme rainfall and floods may particularly increase the risk for young children – who are especially vulnerable to cryptosporidiosis infections - who are living in urban areas – where they are exposed to sewage overflow after to stormwater discharges during extreme weather (Young et al., 2015). Droughts on the other hand can reduce water volumes in reservoirs, natural water bodies and water treatment plant effluents to the extent that pathogen concentrations become problematic (Semenza and Menne, 2009). Generally, an increase in disease risk can be expected with rising temperatures, higher variability of rainfall and more extreme events associated with climate change.

Prevention & Treatment

Prevention

Good sanitary practices
Awareness raising about disease transmission, personal and public hygiene
Protection of water sources and artificial water constructions such as water towers or swimming pools against contamination (Ryan et al., 2016; WHO, 2022)
Case reporting and isolation of patients with a severe outcome
No vaccine against Cryptosporidium parasites available

Treatment

Rehydration, pain medication, electrolyte replacement
Antibiotics or passive antibody therapy in severe cases
Nitazoxanide

Links to further information

References

Cabada, M. M., and White, A. C., 2010, Treatment of cryptosporidiosis: Do we know what we think we know? Current Opinion in Infectious Diseases 23(5), 494–499. https://doi.org/10.1097/QCO.0b013e32833de052

Chako, C. Z., et al., 2010, Cryptosporidiosis in People: It’s Not Just About the Cows, Journal of Veterinary Internal Medicine 24(1), 37–43. https://doi.org/10.1111/j.1939-1676.2009.0431.x

Davies, A. P. and Chalmers, R. M., 2009, Cryptosporidiosis, BMJ 339, b4168. https://doi.org/10.1136/bmj.b4168

ECDC, 2017-2021, Annual epidemiological reports for 2014-2018 – Cryptosporidiosis. Available at https://www.ecdc.europa.eu/en/cryptosporidiosis. Last accessed August 2023.

ECDC, 2023, Surveillance Atlas of Infectious Diseases. Available at https://atlas.ecdc.europa.eu/public/index.aspx. Last accessed August 2023.

Fayer, R. and Nerad, T., 1996, Effects of low temperatures on viability of Cryptosporidium parvum oocysts. Applied and Environmental Microbiology 62(4), 1431-1433. https://doi.org/10.1128/aem.62.4.1431-1433.1996

Gerace, E., et al., 2019, Cryptosporidium infection: Epidemiology, pathogenesis, and differential diagnosis, European Journal of Microbiology and Immunology 9(4), 119–123. https://doi.org/10.1556/1886.2019.00019

Jagai, J. S., et al., 2009, Seasonality of cryptosporidiosis: A meta-analysis approach, Environmental Research 109(4), 465–478. https://doi.org/10.1016/j.envres.2009.02.008

Pane, S. and Putignani, L., 2022, Cryptosporidium: Still Open Scenarios, Pathogens 11(5), 515. https://doi.org/10.3390/pathogens11050515

Patz, J. A., et al., 2000, Effects of environmental change on emerging parasitic diseases. International Journal for Parasitology 30(12–13), 1395–1405. https://doi.org/10.1016/S0020-7519(00)00141-7

Putignani, L. and Menichella, D., 2010, Global Distribution, Public Health and Clinical Impact of the Protozoan Pathogen Cryptosporidium, Interdisciplinary Perspectives on Infectious Diseases 2010, 753512. https://doi.org/10.1155/2010/753512

Ramirez, N. E., et al., 2004, A review of the biology and epidemiology of cryptosporidiosis in humans and animals, Microbes and Infection 6(8), 773–785. https://doi.org/10.1016/j.micinf.2004.02.021

Ryan, U., et al., 2016, Cryptosporidium in humans and animals—A one health approach to prophylaxis, Parasite Immunology 38(9), 535–547. https://doi.org/10.1111/pim.12350

Semenza, J. C. and Menne, B., 2009, Climate change and infectious diseases in Europe, The Lancet Infectious Diseases 9(6), 365–375. https://doi.org/10.1016/S1473-3099(09)70104-5

Sow, S. O., et al., 2016, The Burden of Cryptosporidium Diarrheal Disease among Children < 24 Months of Age in Moderate/High Mortality Regions of Sub-Saharan Africa and South Asia, Utilizing Data from the Global Enteric Multicenter Study (GEMS), PLOS Neglected Tropical Diseases 10(5), e0004729. https://doi.org/10.1371/journal.pntd.0004729

WHO, 2022, World Health Organization, https://www.who.int/. Last accessed August 2022.

Xiao, L. and Feng, Y., 2017, Molecular epidemiologic tools for waterborne pathogens Cryptosporidium spp. And Giardia duodenalis, Food and Waterborne Parasitology 8–9, 14–32. https://doi.org/10.1016/j.fawpar.2017.09.002

Young, I., et al., 2015, A systematic review and meta-analysis of the effects of extreme weather events and other weather-related variables on Cryptosporidium and Giardia in fresh surface waters, Journal of Water and Health 13(1), 1-17. https://doi.org/10.2166/wh.2014.079

[1] Hospitalisation probability is labeled as low, moderate or high when respectively < 25%, 25-75% or > 75% of cases are hospitalized. The probability is based on available data on hospitalisation status of reported cases. In 2020-2021, for about 55% of the cases the hospitalisation status was known.