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Journal of Water and Health Vol 5 No 1 pp 1–38 © IWA Publishing 2007 doi:10.2166/wh.2006.002

Waterborne transmission of protozoan parasites: A worldwide review of outbreaks and lessons learnt

Panagiotis Karanis, Christina Kourenti and Huw Smith

Medical and Molecular Parasitology Laboratory, Centre of Anatomy, Institute II, Medical School, University of Cologne, Joseph-Stelzmann Strasse 9Cologne, 50931, Germany Tel.: +49-221-478-5817 Fax: +49-221-478-3808
Unit for Molecular Epidemiology and Protozoan Pathogenetics, National Research Center for Protozoan Diseases, Obihiro University for Agriculture and Veterinary Medicine, Inada-choObihiro, 080-8555, Japan Tel.: +81-155-49-5644 Fax: +81-155-49-5643 karanis@obihiro.ac.jp
Scottish Parasite Diagnostic Laboratory, Stobhill Hospital, Glasgow G213UW, UK


At least 325 water-associated outbreaks of parasitic protozoan disease have been reported. North American and European outbreaks accounted for 93% of all reports and nearly two-thirds of outbreaks occurred in North America. Over 30% of all outbreaks were documented from Europe, with the UK accounting for 24% of outbreaks, worldwide. Giardia duodenalis and Cryptosporidium parvum account for the majority of outbreaks (132; 40.6% and 165; 50.8%, respectively), Entamoeba histolytica and Cyclospora cayetanensis have been the aetiological agents in nine (2.8%) and six (1.8%) outbreaks, respectively, while Toxoplasma gondii and Isospora belli have been responsible for three outbreaks each (0.9%) and Blastocystis hominis for two outbreaks (0.6%). Balantidium coli, the microsporidia, Acanthamoeba and Naegleria fowleri were responsible for one outbreak, each (0.3%). Their presence in aquatic ecosystems makes it imperative to develop prevention strategies for water and food safety. Human incidence and prevalence-based studies provide baseline data against which risk factors associated with waterborne and foodborne transmission can be identified. Standardized methods are required to maximize public health surveillance, while reporting lessons learned from outbreaks will provide better insight into the public health impact of waterborne pathogenic protozoa.

Keywords: method standardisation; molecular methods; protozoan parasites; validation; waterborne outbreaks; worldwide

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