Determining UV Inactivation of Toxoplasma gondii Oocysts by Using Cell Culture and a Mouse Bioassay

National Exposure Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, Ohio 45268, USA.
Applied and Environmental Microbiology (Impact Factor: 3.67). 08/2010; 76(15):5140-7. DOI: 10.1128/AEM.00153-10
Source: PubMed


The effect of UV exposure on Toxoplasma gondii oocysts has not been completely defined for use in water disinfection. This study evaluated UV-irradiated oocysts by three
assays: a SCID mouse bioassay, an in vitro T. gondii oocyst plaque (TOP) assay, and a quantitative reverse transcriptase real-time PCR (RT-qPCR) assay. The results from the animal
bioassay show that 1- and 3-log10 inactivation is achieved with 4 mJ/cm2 UV and 10 mJ/cm2 low-pressure UV, respectively. TOP assay results, but not RT-qPCR results, correlate well with bioassay results. In conclusion,
a 3-log10 inactivation of T. gondii oocysts is achieved by 10-mJ/cm2 low-pressure UV, and the in vitro TOP assay is a promising alternative to the mouse bioassay.

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Available from: Swinburne A J Augustine
    • "This arrest gives the cells an opportunity to repair the DNA damages induced and continue proliferation and it is possible that something similar happens when Giardia is treated with UV-C. The response to UV-C treatment of three other protozoan parasites , Entamoeba histolytica, Cryptosporidium parvum and Toxoplasma gondii, has recently been published (Ware et al., 2010; Weber et al., 2009; Zhang et al., 2012). In E. histolytica, trophozoites subjected to UV-C treatment were studied using microarrays and the expression of genes encoding Fe—S clusters-containing proteins and DNA repair proteins were reported to be up-regulated, whereas genes associated to the cytoskeleton were repressed (Weber et al., 2009). "
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    ABSTRACT: The response to ultraviolet light (UV) radiation, a natural stressor to the intestinal protozoan parasite Giardia intestinalis, was studied to deepen the understanding of how the surrounding environment affects the parasite during transmission. UV radiation at 10 mJ/cm(2) kills Giardia cysts effectively whereas trophozoites and encysting parasites can recover from UV treatment at 100 mJ/cm(2) and 50 mJ/cm(2) respectively. Staining for phosphorylated histone H2A showed that UV treatment induces double-stranded DNA breaks and flow cytometry analyses revealed that UV treatment of trophozoites induces DNA replication arrest. Active DNA replication coupled to DNA repair could be an explanation to why UV light does not kill trophozoites and encysting cells as efficiently as the non-replicating cysts. We also examined UV-induced gene expression responses in both trophozoites and cysts using RNA sequencing (RNA seq). UV radiation induces small overall changes in gene expression in Giardia but cysts show a stronger response than trophozoites. Heat shock proteins, kinesins and Nek kinases are up-regulated, whereas alpha-giardins and histones are down-regulated in UV treated trophozoites. Expression of variable surface proteins (VSPs) is changed in both trophozoites and cysts. Our data show that Giardia cysts have limited ability to repair UV-induced damage and this may have implications for drinking- and waste-water treatment when setting criteria for the use of UV disinfection to ensure safe water. Copyright © 2015 Elsevier Inc. All rights reserved.
    No preview · Article · Mar 2015 · Experimental Parasitology
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    • "In the environment, oocysts can resist freezing and moderately high temperatures to remain viable for years in soil and water [4,17]. Water chemical and physical treatments, including chlorination and ozone treatment, are not effective in killing oocysts; however, oocysts are relatively susceptible to ultraviolet radiation [18,19]. Although modern municipal water treatment systems (with filtering, coagulation, flocculation, and settling) are generally effective at removing oocysts [4], many populations do not have access to drinking water that has undergone this level of treatment. "
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    ABSTRACT: Background Toxoplasma gondii imparts a considerable burden to public health. Human toxoplasmosis can be life-threatening in immunocompromised individuals, has been associated with psychiatric disorders, and can cause severe congenital pathologies, spontaneous abortion, or stillbirth. Environmental modes of transmission contributing to the incidence of human toxoplasmosis are poorly understood. We sought to examine National Health and Nutrition Examination Survey (NHANES) data for risk factors associated with T. gondii seroprevalence. Methods T. gondii serology results reported for Continuous NHANES survey years 1999–2004 and 2009–10 were examined. To explore associations with toxoplasmosis seropositivity, covariates of interest were selected a priori, including source and home treatment of tap water. Associations between potential risk factors and evidence of IgG antibodies against T. gondii were assessed using multivariable logistic regression. Results Among 23,030 participants with available T. gondii serology across 8 years of continuous NHANES survey data (1999–2004; 2009–2010), persons born outside the United States were significantly more likely to be seropositive, and seropositivity was inversely associated with years spent in the United States. Among US-born participants, participants with homes on well water (both those who used at-home water treatment devices and those who did not), as well as participants with public/private company-provided tap water who did not use at-home water treatment devices, were significantly more likely to be seropositive compared to participants who used home treatment devices on tap water provided by a private or public water company. A comparative subpopulation analysis revealed age-adjusted seroprevalence among US-born persons 12-49 yrs old significantly declined to 6.6% (95% CI, 5.2-8.0) (P <0.0001) in 2009–10, compared to previously published reports for NHANES data from 1988–1994 (14.1%) and 1999–2004 (9.0%). Conclusions Data suggests that T. gondii infections continue to decline in the United States, but the overall infection rate remains substantial at nearly 7%. Despite the limitations in the Continuous NHANES cross-sectional survey, the association between well water use and T. gondii infection warrants further research.
    Full-text · Article · Jul 2014 · BMC Public Health
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    • "Parasite foci were detected after 10 days of incubation by crystal violet staining and counted as a correlate of oocyst (i.e. sporozoite) infectivity (Villegas et al. 2010; Ware et al. 2010). Formalin (10 %) completely prevented, and acidified Clorox R (10 %) considerably reduced parasite reproduction in the TOP assay (Villegas et al. 2010). "
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    ABSTRACT: Chemical disinfection is common practice and inevitable to achieve sufficient control over parasites particularly in intensive animal housing systems. To identify suitable chemicals, reliable data on antiparasitic efficacy of disinfectants are required. This review summarizes recently published experience with procedures applied to evaluate the viability of a variety of endoparasites following physical or chemical stress. It is concluded that laboratory models used to assess antiparasitic efficacy of e.g. commercial disinfectants should consider the most resistant stages of both helminths and protozoa, i.e. ascarid eggs and coccidia oocysts. To ensure reproducibility and transparency, standardized protocols are pivotal. Such protocols are established on a national level (e.g. DVG guidelines in Germany); however, internationally accepted certification procedures are currently lacking.
    Full-text · Article · Feb 2013 · Parasitology Research
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