Cryptosporidium: bridging local outbreaks to global health disparities

In early May, news emerged of numerous Devon (UK) residents experiencing vomiting and diarrhoea. Majorly affecting the Brixham region, over 40 people were diagnosed with cryptosporidiosis, and over 16,000 homes were advised to boil water before consuming it to kill potential pathogens (Fig. 1). Despite a controversial handling of the situation from South West Water (SWW) (from initial denial of the ‘crisis’, to major profit increases for the company), the outbreak was eventually linked to a broken pipe from where animal faeces could have entered, contaminating the water supply, a SWW representative suggested. In this article, we will investigate the disease and its relevance worldwide.

So, what is Cryptosporidiosis?

Cryptosporidiosis is commonly associated with gastrointestinal  symptoms, such as vomiting, diarrhoea and severe abdominal cramps. It is caused by cryptosporidium, from the Apicocomplexa family. This microorganism is an intra-cellular gut parasite which invades the microvilli in the gut and depletes host nutrients. The parasite is spread via faecal-oral transmission, and it is commonly found in contaminated water, food and animals. Its life cycle starts with oocyst (egg) ingestion, leading to attachment to host gut epithelia, and asexual reproduction. This allows sexual reproduction to ensue, and oocyst formation. Eventually, the oocysts are released via faeces, for the cycle of infection to continue.

Cryptosporidium species are often identified by the immune system via Toll-Like Receptors, specifically TLR-4, in the gut epithelia; Cryptosporidium-derived molecules are treated as TLR-4 ligands, since the microbe does not produce LPS molecules. Adaptive immune signalling pathways, such as NF-kB, are triggered, encouraging IL-8, CXCL1 and other chemokine secretion from the gut (Fig.2). Consequently, gut inflammation is increased, as well as levels of Intracellular Adhesion Molecule-1 (ICAM-1), to aid immunocyte recruitment and improve pathogenic clearance. Other mechanisms the epithelial barrier uses to eliminate cryptosporidium infection include NO secretion and mucin production, to kill the pathogen, and prevent further infection by blocking extracellular oocyst binding, respectively. In some individuals, cryptosporidium can evade immune response due to its intracellular nature.

Most immunocompetent patients suffer mild symptoms and so are offered symptomatic treatment, but some immunocompromised patients (those with HIV, for example) can develop chronic diarrhoea as a result of cryptosporidium infection. In this instance, managing fluid loss and rest is often insufficient; these patients are prescribed nitazoxanide, a broad-spectrum antiparasitic, to manage their diarrhoea.

Cryptosporidiosis on a global scale

Although controversial, the management of the cryptosporidium ‘crisis’ in Devon was resolved relatively quickly compared to outbreaks in other countries (Fig.3). 

There are clear links between socio-economic dynamics and water-borne illness prevalence. In some developing regions, such as areas in the Middle East and North Africa (MENA), cryptosporidiosis is considered endemic, due to poor quality water-sanitation centres, rapid population growth and inadequate potable water supply. Globally, 3.4 million people die each year from water-borne illnesses - and poor sanitation ranks higher in causes of human morbidity than war and terrorism. Additionally, in 2015, cryptosporidium was the fourth leading cause of death amongst children under 5, clearly highlighting the danger this parasite can cause. For children in developing countries, who are already predisposed to starvation, cryptosporidiosis can kick-start a malnutrition cycle. Here, cryptosporidium exacerbates host malnutrition due to its parasitic nature, potentially causing cognitive impairment and growth stunting. 

Cryptosporidiosis, although typically mild, can be devastating for some people (the immunocompromised and young children). Particularly, those who are malnourished can suffer severe effects. The water contamination in Devon (UK), handled by SWW, was unfortunate and many in the region experienced severe illness. Globally, cryptosporidiosis is a major problem and in some regions, it is considered endemic. Thus, it is important we spread awareness of the devastating effects of this disease, continue efforts to prevent transmission and strive for eradication.

Written by Eloise Nelson

REFERENCES

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Chalmers, R.M., Davies, A.P. and Tyler, K. (2019) ‘Cryptosporidium’, Microbiology, 165(5), pp. 500–502. doi:10.1099/mic.0.000764.

Hassan, E.M. et al. (2020) ‘A review of cryptosporidium spp. and their detection in water’, Water Science and Technology, 83(1), pp. 1–25. doi:10.2166/wst.2020.515.

News, S. (2024) ‘Brixham: More than 50 people in Devon ill from contaminated water - as South West Water’s owner posts £166m profit’, Sky News, 21 May. Available at: https://news.sky.com/story/brixham-more-than-50-people-in-devon-ill-from-contaminated-water-as-south-west-waters-owner-posts-166m-profit-13140820#:~:text=More%20than%2050%20cases%20of,water%2C%20health%20bosses%20have%20said.

Sparks, H. et al. (2015) ‘Treatment of cryptosporidium: What we know, gaps, and the way forward’, Current Tropical Medicine Reports, 2(3), pp. 181–187. doi:10.1007/s40475-015-0056-9. 

Caccio SM. Cryptosporidium : parasite and disease, Immunology of Cryptosporidiosis. Springer Verlag Gmbh; 2016.