Attempted Detection of Toxoplasma gondii Oocysts in Environmental Waters Using a Simple Approach to Evaluate the Potential for Waterborne Transmission in the Galápagos Islands,Ecuador

Toxoplasmosis is a health concern for wildlife and humans, particularly in island ecosystems. In the Galápagos Islands, exposure to Toxoplasma gondii has been found in marine avifauna on islands with and without domestic cats. To evaluate potential waterborne transmission of T. gondii, we attempted to use filtration and epifluorescent microscopy to detect autofluorescent T. gondii oocysts in fresh and estuarine surface water samples. T. gondii oocyst-like structures were microscopically visualized but were not confirmed by polymerase chain reaction and sequence analyses. Further research is needed to refine environmental pathogen screening techniques and to evaluate disease risk of waterborne zoonoses such as T. gondii for wildlife and humans, particularly in the Galápagos and other naive island ecosystems.     

A New Pathogen Transmission Mechanism in the Ocean: The Case of Sea Otter Exposure to the Land-Parasite Toxoplasma gondii

Toxoplasma gondii is a land-derived parasite that infects humans and marine mammals. Infections are a significant cause of mortality for endangered southern sea otters (Enhydra lutris nereis), but the transmission mechanism is poorly understood. Otter exposure to T. gondii has been linked to the consumption of marine turban snails in kelp (Macrocystis pyrifera) forests. It is unknown how turban snails acquire oocysts, as snails scrape food particles attached to surfaces, whereas T. gondii oocysts enter kelp beds as suspended particles via runoff. We hypothesized that waterborne T. gondii oocysts attach to kelp surfaces when encountering exopolymer substances (EPS) forming the sticky matrix of biofilms on kelp, and thus become available to snails. Results of a dietary composition analysis of field-collected snails and of kelp biofilm indicate that snails graze the dense kelp-biofilm assemblage composed of pennate diatoms and bacteria inserted within the EPS gel-like matrix. To test whether oocysts attach to kelp blades via EPS, we designed a laboratory experiment simulating the kelp forest canopy in tanks spiked with T. gondii surrogate microspheres and controlled for EPS and transparent exopolymer particles (TEP - the particulate form of EPS). On average, 19% and 31% of surrogates were detected attached to kelp surfaces covered with EPS in unfiltered and filtered seawater treatments, respectively. The presence of TEP in the seawater did not increase surrogate attachment. These findings support a novel transport mechanism of T. gondii oocysts: as oocysts enter the kelp forest canopy, a portion adheres to the sticky kelp biofilms. Snails grazing this biofilm encounter oocysts as ‘bycatch’ and thereby deliver the parasite to sea otters that prey upon snails. This novel mechanism can have health implications beyond T. gondii and otters, as a similar route of pathogen transmission may be implicated with other waterborne pathogens to marine wildlife and humans consuming biofilm-feeding invertebrates.     

Toxoplasma gondii: uptake and survival of oocysts in free-living amoebae

Waterborne transmission of the oocyst stage of Toxoplasma gondii can cause outbreaks of clinical toxoplasmosis in humans and infection of marine mammals. In water-related environments and soil, free-living amoebae are considered potential carriers of various pathogens, but knowledge on interactions with parasitic protozoa remains elusive. In the present study, we assessed whether the free-living Acanthamoebacastellanii, due to its phagocytic activity, can interact with T. gondii oocysts. We report that amoebae can internalize T. gondii oocysts by active uptake. Intracellular oocysts in amoebae rarely underwent phagocytic lysis, retained viability and established infection in mice. Interaction of T. gondii with amoebae did not reduce the infectivity and pathogenicity of oocysts even after prolonged co-cultivation. Our results show that uptake of oocysts by A. castellanii does not restrain the transmission of T. gondii in a murine infection model.     

Effect of Estuarine Wetland Degradation on Transport of Toxoplasma gondii Surrogates from Land to Sea

The flux of terrestrially derived pathogens to coastal waters presents a significant health risk to marine wildlife, as well as to humans who utilize the nearshore for recreation and seafood harvest. Anthropogenic changes in natural habitats may result in increased transmission of zoonotic pathogens to coastal waters. The objective of our work was to evaluate how human-caused alterations of coastal landscapes in California affect the transport of Toxoplasma gondii to estuarine waters. Toxoplasma gondii is a protozoan parasite that is excreted in the feces of infected felids and is thought to reach coastal waters in contaminated runoff. This zoonotic pathogen causes waterborne toxoplasmosis in humans and is a significant cause of death in threatened California sea otters. Surrogate particles that mimic the behavior of T. gondii oocysts in water were released in transport studies to evaluate if the loss of estuarine wetlands is contributing to an increased flux of oocysts into coastal waters. Compared to vegetated sites, more surrogates were recovered from unvegetated mudflat habitats, which represent degraded wetlands. Specifically, in Elkhorn Slough, where a large proportion of otters are infected with T. gondii, erosion of 36% of vegetated wetlands to mudflats may increase the flux of oocysts by more than 2 orders of magnitude. Total degradation of wetlands may result in increased Toxoplasma transport of 6 orders of magnitude or more. Destruction of wetland habitats along central coastal California may thus facilitate pathogen pollution in coastal waters with detrimental health impacts to wildlife and humans.Estuaries are recognized as being critically endangered worldwide. Pollution of estuarine waters is a significant threat to the health of aquatic life, as well as to humans who depend on coastal habitats (23). Contamination of nearshore waters with terrestrially derived, zoonotic pathogens has received little attention in the field of marine water pollution, which has primarily focused on chemical and nutrient pollutants (22, 42, 46, 55). Yet, studies have documented the presence of fecal pathogens from terrestrial animals in coastal waters and filter-feeding shellfish (7, 37, 48), as well as infections and deaths in aquatic wildlife and humans who become exposed through recreation activities or seafood (4, 18, 39). The zoonotic parasite Toxoplasma gondii is emerging as an important waterborne pathogen in both human and marine wildlife populations (2, 3, 6, 11, 15, 38). Consumption of raw oysters, clams, or mussels has recently been determined to be a risk factor for human exposure to T. gondii (24). Moreover, this parasite is an important cause of death in threatened Southern sea otters (Enhydra lutris nereis) (10, 29). Sea otter infection appears most likely to result from ingestion of environmentally resistant T. gondii oocysts that reach coastal waters in contaminated freshwater runoff (35, 36). These oocysts are shed in the feces of infected wild and domestic felids, with an individual cat capable of shedding up to 1 billion oocysts over several days postinfection (12).Elkhorn Slough, within Monterey Bay in California, is one of the high-risk sites for sea otter infection with T. gondii, with seroprevalence rates of 79% in otters sampled in this area (35). To date, the reasons for the high sea otter prevalence of infections with T. gondii at this site remain unknown. This estuarine habitat has been extensively altered by human activities and is listed as an impaired body of water by the State of California (9). Specifically, extensive degradation has been observed in the slough, with over one-third of vegetated wetlands converted to mudflats due to erosion (49). While the effect of this landscape alteration on the transport of waterborne pathogens is not currently known, such degradation may facilitate contamination of nearshore waters with T. gondii.Wetland habitats provide valuable ecosystem services, including improvement of effluent water quality characteristics through removal of a variety of pollutants (28, 50, 57). Artificially constructed wetlands are now used globally in water treatment facilities to remove nutrients, chemical pollutants, and fecal pathogens from contaminated waters before discharge into receiving water bodies (8, 17, 21, 26, 27). However, compared with freshwater and constructed wetlands, significantly less research has focused on the effects of natural, estuarine wetlands on water quality. In the few studies that investigated the impact of saltwater marshes on marine water quality, these habitats were shown to reduce concentrations of chemicals and nutrients that reach coastal waters in contaminated overland runoff (5, 51). In addition, the percentage of watershed-impervious surface coverage and reduction of natural coastal habitats due to anthropogenic changes has been associated with increased coastal water pollution (33, 34). Despite previous research suggesting a link between wetland degradation and coastal pathogen pollution (5, 33, 34, 51), the role estuarine wetlands play in the transport of terrestrial pathogens from land to sea has not been previously investigated.The overall goal of our research was to evaluate the effect of coastal wetland degradation on contamination of estuarine and coastal waters with terrestrially derived, zoonotic pathogens. Specifically, the objective of this study was to measure T. gondii oocyst transport through vegetated estuarine wetlands and nonvegetated mudflats to quantify the effect of vegetation loss on the flux of this zoonotic pathogen to coastal waters. Due to the biohazard risks associated with the release of environmentally resistant oocysts, experiments used previously validated surrogate microspheres and a specially designed flume that was deployed in vegetated and mudflat (nonvegetated) estuarine wetland habitats. The flume-in-field study design allowed for replication of experiments using specific hydrological parameters while conducting the study within a natural estuarine environment with in situ vegetation, substrate, and water. The two autofluorescent microspheres used in this study have similar physical and surface chemistry properties to T. gondii oocysts and have been previously evaluated as surrogate particles for this protozoan parasite (44). Our results provide novel insights into the consequences of changes in coastal habitat on the ecology of zoonotic infectious disease organisms in coastal marine ecosystems.     

Waterborne toxoplasmosis - Recent developments

Humans become infected with Toxoplasma gondii mainly by ingesting uncooked meat containing viable tissue cysts or by ingesting food or water contaminated with oocysts from the feces of infected cats. Circumstantial evidence suggests that oocyst-induced infections in humans are clinically more severe than tissue cyst-acquired infections. Until recently, waterborne transmission of T. gondii was considered uncommon, but a large human outbreak linked to contamination of a municipal water reservoir in Canada by wild felids and the widespread infection of marine mammals in the USA provided reasons to question this view. The present paper examines the possible importance of T. gondii transmission by water.     

Obtaining Highly Purified Toxoplasma gondii Oocysts by a Discontinuous Cesium Chloride Gradient

Toxoplasma gondii is an obligate intracellular protozoan pathogen that commonly infects humans. It is a well characterized apicomplexan associated with causing food- and water-borne disease outbreaks. The definitive host is the feline species where sexual replication occurs resulting in the development of the highly infectious and environmentally resistant oocyst. Infection occurs via ingestion of tissue cysts from contaminated meat or oocysts from soil or water. Infection is typically asymptomatic in healthy individuals, but results in a life-long latent infection that can reactivate causing toxoplasmic encephalitis and death if the individual becomes immunocompromised. Meat contaminated with T. gondii cysts have been the primary source of infection in Europe and the United States, but recent changes in animal management and husbandry practices and improved food handling and processing procedures have significantly reduced the prevalence of T. gondii cysts in meat^{1, 2}. Nonetheless, seroprevalence in humans remains relatively high suggesting that exposure from oocyst contaminated soil or water is likely. Indeed, waterborne outbreaks of toxoplasmosis have been reported worldwide supporting the theory exposure to the environmental oocyst form poses a significant health risk^3-5. To date, research on understanding the prevalence of T. gondii oocysts in the water and environment are limited due to the lack of tools to detect oocysts in the environment ^{5, 6}. This is primarily due to the lack of efficient purification protocols for obtaining large numbers of highly purified T gondii oocysts from infected cats for research purposes. This study describes the development of a modified CsCl method that easily purifies T. gondii oocysts from feces of infected cats that are suitable for molecular biological and tissue culture manipulation⁷.     

Waterborne toxoplasmosis investigated and analysed under hydrogeological assessment: new data and perspectives for further research

We present a set of data on human and chicken Toxoplasma gondii seroprevalence that was investigated and analysed in light of groundwater vulnerability information in an area endemic for waterborne toxoplasmosis in Brazil. Hydrogeological assessment was undertaken to select sites for water collection from wells for T. gondii oocyst testing and for collecting blood from free-range chickens and humans for anti-T. gondii serologic testing. Serologic testing of human specimens was done using conventional commercial tests and a sporozoite-specific embryogenesis-related protein (TgERP), which is able to differentiate whether infection resulted from tissue cysts or oocysts. Water specimens were negative for the presence of viable T. gondii oocysts. However, seroprevalence in free-range chickens was significantly associated with vulnerability of groundwater to surface contamination (p < 0.0001; odds ratio: 4.73, 95% confidence interval: 2.18-10.2). Surprisingly, a high prevalence of antibodies against TgERP was detected in human specimens, suggesting the possibility of a continuous contamination of drinking water with T. gondii oocysts in this endemic setting. These findings and the new proposed approach to investigate and analyse endemic toxoplasmosis in light of groundwater vulnerability information associated with prevalence in humans estimated by oocyst antigens recognition have implications for the potential role of hydrogeological assessment in researching waterborne toxoplasmosis at a global scale.     

Development of a PCR-Enzyme Immunoassay Oligoprobe Detection Method for Toxoplasma gondii Oocysts, Incorporating PCR Controls

Infections caused by Toxoplasma gondii are widely prevalent in animals and humans throughout the world. In the United States, an estimated 23% of adolescents and adults have laboratory evidence of T. gondii infection. T. gondii has been identified as a major opportunistic pathogen in immunocompromised individuals, in whom it can cause life-threatening disease. Water contaminated with feces from domestic cats or other felids may be an important source of human exposure to T. gondii oocysts. Because of the lack of information regarding the prevalence of T. gondii in surface waters, there is a clear need for a rapid, sensitive method to detect T. gondii from water. Currently available animal models and cell culture methods are time-consuming, expensive, and labor-intensive, requiring days or weeks for results to be obtained. Detection of T. gondii nucleic acid by PCR has become the preferred method. We have developed a PCR amplification and detection method for T. gondii oocyst nucleic acid that incorporates the use of hot-start amplification to reduce nonspecific primer annealing, uracil-N-glycosylase to prevent false-positive results due to carryover contamination, an internal standard control to identify false-negative results due to inadequate removal of sample inhibition, and PCR product oligoprobe confirmation using a nonradioactive DNA hybridization immunoassay. This method can provide positive, confirmed results in less than 1 day. Fewer than 50 oocysts can be detected following recovery of oocyst DNA. Development of a T. gondii oocyst PCR detection method will provide a useful technique to estimate the levels of T. gondii oocysts present in surface waters.     

Toxoplasma gondii: protection against colonization of the brain and muscles in a rat model

The objective was to test immune protection against the formation of Toxoplasma gondii tissue cysts in rats. It has been previously shown that 50 T. gondii tissue cysts of strain Me49 are not pathogenic for CF-1 mice, whereas 1 T. gondii tissue cyst of strain M-7741, can be lethal for mice 11-13 days after subcutaneous or oral administration. In the present study, ten rats were fed T. gondii oocysts of strain Me49 and after a further 30 days they were each orally challenged with T. gondii oocysts of strain M-7741. Thirty days after this, they were euthanased and brain and muscle samples inoculated subcutaneously or orally dosed, respectively, to mice for bioassay. None of the mice died, whereas all the mice that were inoculated with brain homogenates or were fed muscle samples from four non-immunized rats that had been inoculated with T. gondii oocysts of strain M-7741, died. These results encourage further research towards achieving vaccinal protection against the formation of T. gondii tissue cysts in meat animals and people.     

Development of Toxoplasma gondii Chinese I genotype Wh6 Strain in Cat Intestinal Epithelial Cells

Felids are the unique definitive host of Toxoplasma gondii. The intestine of felid is the only site for initiating Toxoplasma gondii sexual reproduction. T. gondii excretes millions of infectious oocysts from the intestine, which are the primary source of infection. There are many difficulties in developing vaccines and drugs to control oocyst excretion due to the lack of an appropriate experimental model. Here, we established an in vitro feline intestinal epithelial cell (IEC) infection system and an efficient animal model of T. gondii Chinese 1 genotype, Wh6 strain (TgCtwh6). The Kunming mice brain tissues containing TgCtwh6 cysts were harvested 42-day post-infection. The bradyzoites were co-cultured with cat IECs in vitro at a ratio of 1:10. Five 3-month-old domestic cats were orally inoculated with 600 cysts each. The oocysts were detected by daily observation of cat feces by microscopy and polymerase chain reaction. We found that the parasite adhered and invaded cat IECs in vitro, transformed into tachyzoites, and then divided to form rose-like structures. These parasites eventually destroyed host cells, escaped, and finished the asexual reproduction process. Schizonts associated with sexual reproduction have not been observed during development in vitro cultured cells. However, schizonts were detected in all infected cat intestinal epithelial cells, and oocysts were presented in all cat feces. Our study provides a feasible cell model and an efficient infection system for the following studies of T. gondii sexual reproduction, and also lays a foundation to develop drugs and vaccines for blocking excretion and transmission of oocysts.     

Toxoplasma gondii seroprevalence in goats,cats and humans in Russia

Toxoplasmosis, a most common zoonosis, is caused by the protozoan parasite Toxoplasma gondii. However, there is little epidemiological information on T. gondii infections in humans and livestock animals in Russia. Therefore, in this study, the seroprevalence of T. gondii in goats in Russia was investigated. A total of 216 goats from 32 farms were investigated and 95 of them were seropositive for T. gondii. The difference in seroprevalence between the examined regions was not statistically significant. We next collected serum samples from 99 cats and 181 humans in Kazan city, the state capital of the Republic of Tatarstan, Russia, and examined their T. gondii seroprevalences. Thirty-nine of the 99 cat samples and 56 of the 181 human samples showed seropositivity. Logistical regression analysis revealed that the cat breeding history of the human subjects, but not their sex or age is a significant risk factor for T. gondii seropositivity. These findings suggest that the natural environment in Russia may be widely polluted with T. gondii oocysts shed by cats, and ingestion of these oocysts provides a major route for human infection with this parasite.     

Toxoplasma gondii: an improved rat model of congenital infection

The objective of this study was to refine the rat model of congenital toxoplasmosis. In Fischer rats we found that visualization of spermatozoa in vaginal exudates and the detection of at least 6 g body weight increase between days 9 and 12 of pregnancy, allowed the diagnosis and timing of pregnancy with 60% specificity and 84% sensitivity. A dose of 10⁴Toxoplasma gondii bradyzoites or 10²T. gondii oocysts of the Prugniaud strain resulted in more than 50% of congenital infection of the rat litters. Transmission of T. gondii via lactation was not detected in rats inoculated with either bradyzoites or oocysts. Bioassays of 51 neonates born from mothers inoculated with bradyzoites (in tissue cysts) and 29 neonates from mothers inoculated with oocysts demonstrated that both liver and lungs can be used for the diagnosis of congenital transmission in this model.     

An Experimental Toxoplasma gondii Dose Response Challenge Model to Study Therapeutic or Vaccine Efficacy in Cats

High numbers of Toxoplasma gondii oocysts in the environment are a risk factor to humans. The environmental contamination might be reduced by vaccinating the definitive host, cats. An experimental challenge model is necessary to quantitatively assess the efficacy of a vaccine or drug treatment. Previous studies have indicated that bradyzoites are highly infectious for cats. To infect cats, tissue cysts were isolated from the brains of mice infected with oocysts of T. gondii M4 strain, and bradyzoites were released by pepsin digestion. Free bradyzoites were counted and graded doses (1000, 100, 50, 10), and 250 intact tissue cysts were inoculated orally into three cats each. Oocysts shed by these five groups of cats were collected from faeces by flotation techniques, counted microscopically and estimated by real time PCR. Additionally, the number of T. gondii in heart, tongue and brains were estimated, and serology for anti T. gondii antibodies was performed. A Beta-Poisson dose-response model was used to estimate the infectivity of single bradyzoites and linear regression was used to determine the relation between inoculated dose and numbers of oocyst shed. We found that real time PCR was more sensitive than microscopic detection of oocysts, and oocysts were detected by PCR in faeces of cats fed 10 bradyzoites but by microscopic examination. Real time PCR may only detect fragments of T. gondii DNA without the presence of oocysts in low doses. Prevalence of tissue cysts of T. gondii in tongue, heart and brains, and anti T. gondii antibody concentrations were all found to depend on the inoculated bradyzoite dose. The combination of the experimental challenge model and the dose response analysis provides a suitable reference for quantifying the potential reduction in human health risk due to a treatment of domestic cats by vaccination or by therapeutic drug application.     

Toxoplasma gondii: Evidence for the transmission by semen in dogs

Ten male dogs were distributed into three experimental groups for infection with Toxoplasma gondii: GI - three dogs inoculated with 2.0 × 10⁵ P strais oocysts, GII - three dogs infected with 1.0 × 10⁶ RH strain tachyzoites, and GIII - four controls dogs. Several clinical parameters were evaluated. IFAT was performed to detect anti-T. gondii antibodies. Presence of the parasite in semen was evaluated by PCR and bioassay techniques. Tissue parasitism was examined using bioassays and immunohistochemistry in testicle and epididymis fragments collected after orchiectomy. In semen samples collected from these two groups, the presence of T. gondii was verified by bioassays and PCR. T. gondii was detected by immunohistochemistry in tissues (testicle and epididymis fragments) of all six experimentally infected dogs. The T. gondii-positive seminal samples were used in the artificial insemination (AI) of four female dogs free of toxoplasmic infection. Seven days after AI, all of the female dogs presented serologic conversion (IFAT). Fetal reabsorption occurred in two of the dogs, while the others sustained full-term gestation. Several T. gondii cysts were detected in the brains of four offspring. These results suggest that T. gondii can be sexually transmitted in domestic dogs.     

Toxoplasma gondii in humans and animals in Japan: An epidemiological overview

Toxoplasmosis is a cosmopolitan protozoan zoonosis caused by Toxoplasma gondii infamous for inducing severe clinical manifestations in humans. Although the disease affects at least one billion people worldwide, it is neglected in many countries including developed ones. In literature, the epidemiological data documenting the actual incidence of the disease in humans and domestic animals from Japan are limited and importantly many earlier papers on T. gondii infections were published in Japanese and a considerable part is not available online. Herein, we review the current summary about the epidemiological situation of T. gondii infection in Japan and the potential associated risk factors in humans and animals as well as the different T. gondii genotypes isolated in Japan. Several T. gondii isolates have been identified among cats (TgCatJpTy1/k-3, TgCatJpGi1/TaJ, TgCatJpObi1 and TgCatJpOk1–4) and goats (TgGoatJpOk1–13). This literature review underscores the need for a nationwide investigation of T. gondii infection in Japanese people and assessment of the socioeconomic impact of the disease burden. Furthermore, epidemiological studies in domestic and wild animals and estimation of degree of contamination of soil or water with T. gondii oocysts are needed, for a better understanding of the scope of this public health concern.     

Prevalence of anti-Toxoplasma gondii antibody in domestic horses in Japan

The present study is the first report that investigated the seroprevalence of Toxoplasma gondii infection in domestic horses in various prefectures of Japan and analyzed risk factors for seropositivity. We performed a latex agglutination test for riding/racing horses from 11 prefectures in Japan (783 samples) and 4 groups of Japanese native horses (254 samples). The total seroprevalence of anti-T. gondii antibody in horses examined in this study was 4.24% (44/1037). As for riding/racing horses, we did not find a statistically different T. gondii seroprevalence between sampling prefectures. In contrast, seroprevalence of T. gondii in older horses (> 21 years) was significantly higher than that in younger horses (< 5 years and 11–15 years). There was no significant difference in T. gondii seroprevalence between riding/racing horses and Japanese native horses. Logistical regression analysis revealed that age, but not sex and usage, is a significant risk factor of T. gondii infection for domestic horses in Japan. These findings suggest that domesticated horses in Japan can be horizontally infected with T. gondii by ingestion of food or water contaminated with oocysts.     

Physical Inactivation of Toxoplasma gondii Oocysts in Water

Inactivation of Toxoplasma gondii oocysts occurred with exposure to pulsed and continuous UV radiation, as evidenced by mouse bioassay. Even at doses of ≥500 mJ/cm², some oocysts retained their viability.     

Control of human toxoplasmosis

Toxoplasmosis is caused by Toxoplasma gondii, an apicomplexan parasite that is able to infect any nucleated cell in any warm-blooded animal. Toxoplasma gondii infects around 2 billion people and, whilst only a small percentage of infected people will suffer serious disease, the prevalence of the parasite makes it one of the most damaging zoonotic diseases in the world. Toxoplasmosis is a disease with multiple manifestations: it can cause a fatal encephalitis in immunosuppressed people; if first contracted during pregnancy, it can cause miscarriage or congenital defects in the neonate; and it can cause serious ocular disease, even in immunocompetent people. The disease has a complex epidemiology, being transmitted by ingestion of oocysts that are shed in the faeces of definitive feline hosts and contaminate water, soil and crops, or by consumption of intracellular cysts in undercooked meat from intermediate hosts. In this review we examine current and future approaches to control toxoplasmosis, which encompass a variety of measures that target different components of the life cycle of T. gondii. These include: education programs about the parasite and avoidance of contact with infectious stages; biosecurity and sanitation to ensure food and water safety; chemo- and immunotherapeutics to control active infections and disease; prophylactic options to prevent acquisition of infection by livestock and cyst formation in meat; and vaccines to prevent shedding of oocysts by definitive feline hosts.     

Detection of Toxoplasma gondii Oocysts in Drinking Water

The world’s largest outbreak of waterborne toxoplasmosis occurred in a municipality in the western Canadian province of British Columbia. When drinking water emerged as a possible source of infection during the outbreak investigation, a laboratory method was needed to attempt detection of the parasite, Toxoplasma gondii. The method developed was based on the current U.S. Environmental Protection Agency method for detection of Cryptosporidium oocysts. Collection of large-volume drinking water samples and cartridge filter processing were unchanged, although identification of Toxoplasma oocysts in the filter retentate was carried out by using a previously described rodent model. Validation of the method developed was tested by using oocysts from a well-characterized Toxoplasma strain.