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.

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Two methods, centrifugation and flocculation, were evaluated to determine their efficiencies of recovery of Toxoplasma gondii oocysts from contaminated water samples. Demineralized and tap water replicates were inoculated with high numbers of sporulated or unsporulated T. gondii oocysts (1 ؋ 10 5 and 1 ؋ 10 4 oocysts). The strain, age, and concentration of the seeded oocysts were recorded. Oocysts were recovered either by centrifugation of the contaminated samples at various g values or by flocculation with two coagulants, Fe 2 (SO 4 ) 3 and Al 2 (SO 4 ) 3 . The recovery rates were determined with the final pellets by phase-contrast microscopy. Sporulated oocysts were recovered more effectively by flocculation with Al 2 (SO 4 ) 3 (96.5% ؎ 21.7%) than by flocculation with Fe 2 (SO 4 ) 3 (93.1% ؎ 8.1%) or by centrifugation at 2,073 ؋ g (82.5% ؎ 6.8%). For the unsporulated oocysts, flocculation with Fe 2 (SO 4 ) 3 was more successful (100.3% ؎ 26.9%) than flocculation with Al 2 (SO 4 ) 3 (90.4% ؎ 19.1%) or centrifugation at 2,565 ؋ g (97.2% ؎ 12.5%). The infectivity of the sporulated oocysts recovered by centrifugation was confirmed by seroconversion of all inoculated mice 77 days postinfection. These data suggest that sporulated Toxoplasma oocysts purified by methods commonly used for waterborne pathogens retain their infectivity after mechanical treatment and are able to induce infections in mammals. This is the first step in developing a systematic approach for the detection of Toxoplasma oocysts in water.Infections by the apicomplexan parasite Toxoplasma gondii are prevalent in humans and animals throughout the world. This ubiquitous parasite induces more severe illness in the intermediate hosts (mice, pigs, humans) than in the definitive host (cats) (8). However, only the definitive host releases oocysts into the environment through contaminated feces. The excreted oocysts are unsporulated and not immediately infective. Formation of infective sporozoites within sporulated oocysts requires 1 to 5 more days and occurs in the outside environment. Thus, ingestion of food or water contaminated with oocysts from infected cat feces is a common route for postnatal transmission of T. gondii in humans.Ingestion of tissue cysts by consumption of infected meat is another significant source of human infection. Several foodborne outbreaks of toxoplasmosis have been reported worldwide (4-6, 13-15). These outbreaks were attributed mainly to consumption of raw or inadequately cooked meat or to ingestion of raw goat's milk (4, 15). Tissue cysts of T. gondii are killed by cooking and freezing (7), whereas oocysts are more resistant to such treatments and can survive for months in adverse environments.The first reported waterborne toxoplasmosis outbreak was among United States Army soldiers in Panama in 1979. An investigation implicated drinking water obtained from a stream presumably contaminated with oocysts excreted by jungle cats as the source of the organism (2). When the largest documented waterborne outbreak of acute toxop...

Aims:  To describe the development, evaluation and applicability of a complete method for the detection of Toxoplasma gondii in water. Methods and Results:  The method incorporated concentration of water samples by Al2(SO4)3‐flocculation, purification by discontinuous sucrose gradients and detection of toxoplasmic DNA by 18S‐rRNA nested PCR. Tap water replicates and natural water samples were seeded with defined numbers of Toxoplasma oocysts and processed for evaluation studies. When applied to environmental samples, the method gave highest detection sensitivities of 100 oocysts in river water and 10 oocysts in well‐ and sea water. The method was finally applied in 60 water samples of different quality and origin collected over a 14‐month period. Toxoplasmic DNA was detected in four samples. Conclusions:  The method offers an alternative towards improving current methods that can be used for the detection of Toxoplasma oocysts in environmental water samples. Significance and Impact of the Study:  The method in its current form will be helpful for assessment of Toxoplasma contamination in water resources, particularly after outbreak events.

Toxoplasma gondii is becoming a potential threat for public water supplies worldwide, as demonstrated by the occurrence of waterborne toxoplasmosis outbreaks in developing countries as well as industrialised countries. The aim of the present study was to develop a sensitive molecular approach (PCR) for the detection of Toxoplasma oocysts in water. Sporulated and unsporulated T. gondii oocysts (strains DX and AHC1) were isolated from faeces of laboratory-infected cats. After purification and enumeration, oocysts were spiked into 1 -L water replicates and concentrated using centrifugation, Al2(SO4)3 or Fe2(SO4)3 flocculation. DNA was extracted from the concentrated pellets, and a universal primer and a T. gondii-specific primer were selected to amplify a region at the small subunit ribosomal RNA gene. A theoretical detection limit of 0.1 oocysts was achieved for samples that had been concentrated using centrifugation or Al2(SO4)3 flocculation. No PCR products were generated for samples that had been pre-treated using Fe2(SO4)3 flocculation. The final target would be the development of a complete technique able to work as a diagnostic tool for the detection of Toxoplasma in environmental and drinking water.