Scavenger receptors mediate increased uptake of irradiated T.gondii extracts by J774 macrophages.

PURPOSE: Protein extracts developed increased immunogenicity without the aid of adjuvants after gamma irradiation. Gamma irradiation of snake venom increased antivenin production by detoxification and enhanced immunity, probably due preferential uptake of irradiated venoms by macrophage scavenger receptors. We studied this uptake of irradiated soluble Toxoplasma gondii extract (STag) by the J774 macrophage cell line similar to antigen presenting cells. MATERIAL AND METHODS: We labeled STag by biosynthesis in living tachyzoites with radioactive amino acids before purification and irradiation or by adding labels as biotin or fluorescein in stored STag, for quantitative studies or subcellular distribution visualization. RESULTS: There was enhanced binding and uptake of irradiated STag into the cells compared to non-irradiated STag. Using fluorescein labeled antigens and morphological assays, we confirmed that cells avidly ingested both native and irradiated proteins but native STag were digested after ingestion while irradiated proteins remained in the cell, suggesting diverse intracytoplasmic pathways. Native or irradiated STag present the same in vitro sensitivity to three types of peptidases. Inhibitors of scavenger receptors (SRs) such as Dextran sulfate (SR-A1 blocker) or Probucol (SR-B blocker) affect the specific uptake of irradiated antigens, suggesting its association with enhanced immunity. CONCLUSIONS: Our data suggests that cell SRs recognize irradiated proteins, mainly SRs for oxidized proteins, leading to antigen uptake by an intracytoplasmic pathway with fewer peptidases that prolongs presentation to nascent major histocompatibility complex I or II and enhances immunity by better antigen presentation.

Gamma Radiation-Attenuated Toxoplasma gondii Provokes Apoptosis in Ehrlich Ascites Carcinoma-Bearing Mice Generating Long-Lasting Immunity.

PURPOSE: Pathological angiogenesis and apoptosis evasions are common hallmarks of cancer. A different approach to the antitumor effect of parasitic diseases caused by certain protozoans and helminthes had been adopted in recent years as they can affect many cancer characteristics. The present work is an attempt to assess the effect of gamma radiation-attenuated Toxoplasma gondii ME49 as an antiapoptotic and angiogenic regulator modifier on tumor growth aimed at improving cancer protective protocols. METHODS: Attenuated Toxoplasma gondii ME49 was administered orally to mice 2 weeks before inoculation with Ehrlich ascites carcinoma to allow stimulation of the immune response. Hepatic histopathology and immune responses were determined for each group. RESULTS: Marked suppression of the tumor proliferation with induction of long-lasting immunity by stimulating interferon γ and downregulating transforming growth factor ß. The level of tumor promoting inflammatory markers (STAT-3 and tumor necrosis factor α), the angiogenic factors (vascular endothelial growth factor A, integrin, and matrix metallopeptidase 2 and matrix metallopeptidase 9), as well as nitric oxide concentration were significantly decreased. This was collimated with an improvement in apoptotic regulators (cytochrome-c, Bax, Bak, and caspase 3) in liver tissues of vaccinated mice group compared to Ehrlich ascites carcinoma-bearing one. Moreover, the histopathological investigations confirmed this improvement. CONCLUSION: Hence, there is an evidence of potency of radiation attenuated Toxoplasma vaccine in immune activation and targeting tumor cell that can be used as a prophylactic or an adjuvant in combination with chemotherapeutic drugs.

Immunomodulatory activity of gamma radiation-attenuated Toxoplasma gondii in adjuvant arthritic mice.

There is growing evidence that some parasitic infections can impact a variety of autoimmune diseases by disease-inducing or protecting capacities. Anti-inflammatory molecules secreted by Toxoplasma gondii and other parasites are capable of preventing some autoimmune disease like arthritis, lupus nephritis and systemic lupus erythematosus by acting on the immune system. Here we aimed to evaluate the protective efficacy of vaccination with Toxoplasma gondii (T. gondii), either gamma radiation-attenuated or not, on an adjuvant arthritis mouse model. Forty female Swiss albino mice were conducted in experiment divided into normal control; mice were injected with Complete Freund's adjuvant (CFA) into the right hind paws; mice vaccinated with irradiated T. gondii in the 3rd group and un-irradiated T. gondii in the 4th group then were injected two weeks later with CFA. Histopathological changes and IL-17, STAT6 and ROR-γ levels in the joints, as well as serum survivin and Anti-CCP, were evaluated. Also, the splenic production of TGF-ß1, TGF-ßR, IL-23, IL-1ß, IFN-γ, TFN-∞, NFKß, MMP1 and MMP3 were assessed. Results exhibited an enhancement of the histopathological changes with diminished the rise of IL-17, STAT 6 and ROR- γ within the joints of both vaccinated groups. Also, serum survivin and Anti-CCP, as well as splenic inflammatory cytokines were reduced. It can be concluded that vaccination with un-irradiated or radiation-attenuated T. gondii exerted a protective effect against adjuvant arthritis with better pathological achievement in the radiation-attenuated vaccinated group. Using gamma radiation-attenuated parasite to exclude the delirious effects of imposing infection of live one may pave the way to new preventative modality against rheumatoid arthritis.

Vaccination with gamma radiation-attenuated Toxoplasma gondii protects against ovarian infiltration in mice-bearing Ehrlich ascites carcinoma.

Purpose: Cancer is one of the most common causes of mortality and morbidity worldwide. Vaccines have been emerged as an attractive approach for their capacity of eliciting long-term immune response targeting cancer cells. Attenuated avirulent Toxoplasma gondii stimulate immunity and activate antitumor cells thereby eliciting rejection of some established cancer. The purpose of this study was to evaluate the antitumor-protective capacity of vaccination with gamma radiation-attenuated T. gondii against ovarian penetration in Ehrlich ascites carcinoma (EAC)-bearing mice.Materials and methods: Forty-five mice were randomly divided into three groups as follows: nontumor-bearing (normal control); EAC-bearing group (EAC); and mice vaccinated orally with gamma radiation-attenuated T. gondii then inoculated 2 weeks later with EAC (TG + EAC). Survival rate, serum interleukin-12 (IL-12), and levels of IFN-γ mRNA, CD4, and CD8 in ovarian tissues homogenate were assessed. Also, ovarian histopathology and immunohistochemical expressions of metalloproteinase-2, CD34, and vimentin were determined.Results: The group vaccinated with attenuated T. gondii showed significantly increased survival rates, serum IL-12, and levels of IFN-γ, CD4, and CD8 in ovarian tissue homogenates as well as an enhancement of histopathological and immunohistochemical changes compared to EAC-bearing group.Conclusion: Vaccination with gamma radiation-attenuated T. gondii has the capacity to supply immunoprotective impact against ovarian invasion in EAC-bearing mice.

Radiation effects on Toxoplasma antigens: different immune responses of irradiated intact tachyzoites or soluble antigens in experimental mice models.

Purpose: Purpose: Protein irradiation causes aggregation, chain breakage, and oxidation, enhancing its uptake by antigen-presenting cells. To evaluate if irradiated proteins participate on the protection, we studied the immune response induced in mice immunized with irradiated soluble extracts of T. gondii tachyzoites (STag) or irradiated intact T. gondii RH tachyzoites (RH0.25 kGy).Material and Methods: Soluble extracts of Toxoplasma gondii tachyzoites (STag) were irradiated at different dose by Cobalt-60 source. By polyacrylamide gel electrophoresis (SDS-Page) we evaluated the effects on primary structures of protein STags induced by irradiation. By Enzyme-linked Immunosorbent Assay (ELISA) we evaluated the difference between humoral immune response induced by irradiated STag or RH tachyzoites in immunized mice from the detection of specific immunoglobulin G (IgG) antibodies in the serum of immunized mice. From challenge with viable RH strain of T. gondii we evaluated the protection induced in the immunized animals. By cytometry we performed the phenotyping of T and B lymphocytes in the peripheral blood of the immunized animals.Results: Irradiation dose of 1.5 kGy induced minimal changes in most proteins, without affecting their antigenicity or immunogenicity. Immunization showed saturation at the dose of 10 µg/mice, with worst response at higher doses. STag irradiated at 1.5 kGy (STag1.5 kGy) induced higher survival and protection similar to T. gondii RH strain irradiated at 0.25 kGy (RH0.25 kGy), with higher serum levels of high affinity IgG compared to STag native. Blood immune memory cells of mice immunized with STag1.5 kGy had higher proportions of CD19+ (cluster of differentiation 19) and CD4+ (cluster of differentiation 14) cells, whereas mice RH0.25 kGy had high proportion of memory CD8+ (cluster of differentiation 8) cells.Conclusions: Our data suggest that major histocompatibility complex type I (MHCI) pathway, appears seem to be used by RH0.25 kGy to generate cytotoxic cells while STag1.5 kGy uses a major histocompatibility complex type II (MHCII) pathway for B-cell memory, but both induce sufficient immune response for protection in mice without any adjuvant. Irradiation of soluble protein extracts enhances their immune response, allowing similar protection against T. gondii in mice as compared to irradiated intact parasites.

The course of infection with Toxoplasma gondii RH strain in mice pre-vaccinated with gamma irradiated tachyzoites.

Toxoplasma gondii is a ubiquitous protozoan of major medical and veterinary importance. Its treatment is difficult since the available drugs have severe side effects and reactivation may occur anytime. Vaccination with irradiated parasites exhibits ideal characteristics for vaccine development. In our experimental mice model, the protection against challenge with the virulent RH strain was assessed, using 255Gy irradiated tachyzoites. Eighty mice were allocated into 3 groups: naive control group, challenged with virulent RH tachyzoites group and a third group which is challenged with 1 × 106 irradiated tachyzoites, administered as two biweekly doses intraperitoneally. Protection was tested by challenging vaccinated mice with the virulent type RH tachyzoites 30 days after the 2nd vaccination dose. The assessment was built on qualitative clinical, quantitative parasitological, histopathological parameters and measurement of serum Nitric Oxide (NO). The results showed prolonged survival rate, absence of tachyzoites in the peritoneal aspirate by counting, absence of tachyzoites in all examined organs by impression smears, amelioration of histopathological changes in the liver, spleen, brain and lung specimens and increase of the serum NO level in the vaccinated group. Therefore, we propose that irradiated Toxoplasma tachyzoites confer protection for challenged mice and could be an alternative immunization schedule for vaccine development especially for who are at risk of severe immunosuppression.

A review on inactivation methods of Toxoplasma gondii in foods.

Toxoplasmosis is an infection caused by Toxoplasma gondii, a widespread zoonotic protozoan which poses a great threat to human health and economic well-being worldwide. It is usually acquired by ingestion of water contaminated with oocysts from the feces of infected cats or by the ingestion of raw or undercooked foodstuff containing tissue cysts. The oocyst can contaminate irrigation water and fresh edible produce. It is estimated that approximately one-third of the human population worldwide harbor this parasite. Infection with T. gondii is an important cause of diseases of the central nervous system and the eye in immunocompromised and immunocompetent individuals. The purpose of this study was to evaluate the efficacy and applicability of thermal (heating, cooking, freezing and low temperature), non-thermal (high pressure processing, ionizing irradiation and curing) and chemical and biochemical (disinfection, essential oils and biochemical methods such as enzymes, nanoparticles, antibiotics and immune response) treatments for the inactivation, inhabitation or to kill T. gondii in foodstuff intended for public consumption and under experimental conditions.

Gamma irradiation of Toxoplasma gondii protein extract improve immune response and protection in mice models.

Gamma radiation induces protein changes that enhance immunogenicity for venoms, used in antivenin production. Coccidian parasites exposed to gamma radiation elicit immune response with protection in mice and man, but without studies on the effect of gamma radiation in soluble acellular extracts or isolated proteins. Toxoplasmosis is a highly prevalent coccidian disease with only one vaccine for veterinary use but with remaining tissue cysts. Total parasite extracts or recombinant proteins used as immunogen induce usually low protection. Here, we study gamma radiation effect on T. gondii extracts proteins (STAG) and its induced immunity in experimental mice models. By SDS-PAGE, protein degradation is seen at high radiation doses, but at ideal dose (1500 Gy), there are preservation of the antigenicity and immunogenicity, detected by specific antibody recognition or production after mice immunization. Immunization with STAG irradiated at 1500 Gy induced significant protection in mice immunized and challenged with distinct T. gondii strains. In their blood, higher levels of specific CD19+, CD3+CD4+ and CD3+CD8+ activated cells were found when compared to mice immunized with STAG. Irradiated T. gondii tachyzoites extracts induce immune response and protection in mice in addition, could be a feasible alternative for Toxoplasma vaccine.

Disodium cromoglycate may act as a novel adjuvant for UV-attenuated Toxoplasma gondii vaccine in mouse model.

We have proven the beneficial effects during acute Toxoplasma gondii infection when mast cells were inhibited by disodium cromoglycate (DSCG). Here we investigated the adjuvant effect of DSCG on the protective efficacy of UV-attenuated T. gondii (UV-Tg) vaccine. Mice were infected with 102Tg alone or infected with 102Tg plus DSCG (Tg + DSCG), immunized with 105 UV-Tg and challenged with 102Tg (UV-Tg + Tg) or immunized with 105 UV-Tg plus DSCG and challenged with 102Tg (UV-Tg + DSCG + Tg). Compared to Tg group, Tg + DSCG, UV-Tg + Tg, and UV-Tg + DSCG + Tg showed significantly prolonged survival times, decreased parasite burdens, reduced liver histopathologies, and increased levels of Th1 and Th2 cytokines and IL-17 in the livers and spleens by using quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR). Compared to UV-Tg + Tg, UV-Tg + DSCG + Tg had significantly longer survival time, lower tissue parasite burden and histopathological score, and higher levels of Th1 and Th2 cytokines and IL-17 in the livers or spleens. Our data suggest that DSCG may play an adjuvant role in the immunization induced by UV-attenuated T. gondii in mice, by promoting cellular immune response against T. gondii challenge.

A comprehensive analysis of direct and photosensitized attenuation of Toxoplasma gondii tachyzoites.

In the present work, we have evaluated the effect of three different types of radiation: UVC (254±5nm), UVA (365±20nm) and visible (420±20nm) on different morphological and biological functions of Toxoplasma gondii tachyzoites. Briefly, UVC and UVA showed an inhibitory effect on parasite invasion in a dose-dependent manner. UVC showed the strongest effect inducing both structural damage (antigens) and functional inhibition (i.e., invasion and replication). On its own, visible light induces a quite distinctive and selective pattern of parasite-attenuation. This type of incident radiation inhibits the replication of the parasite affecting neither the capability of invasion/attachment nor the native structure of proteins (antigens) on parasites. Such effects are a consequence of photosensitized processes where phenol red might act as the active photosensitizer. The potential uses of the methodologies investigated herein are discussed.

Immunization of Wistar female rats with 255-Gy-irradiated Toxoplasma gondii: Tissue parasitic load and lactogenic quantification.

Toxoplasma gondii is one of the most significant parasite, due its importance in veterinary medicine and in public health, considered a food-borne pathogens, there is no available drug treatments to eliminate it from animal tissue, this reinforce the search for a vaccine against this parasite. This study was aimed to evaluate the dynamic of the distribution of T. gondii in tissues of female Wistar rats and their milk, after the immunization by oral rote with irradiated tachyzoites. One week after pregnancy confirmation, rats was challenged by gavage with T. gondii bradyzoites, oocysts or tachyzoites of T. gondii. Forty-eight pregnant rats were grouped as follows: immunized and challenged with bradyzoites (BZ*); non-immunized and challenged with bradyzoites (BZ); immunized and challenged with oocysts (OC*); non-immunized and challenged with oocysts (OC); immunized and challenged with tachyzoites (TZ*); non-immunized and challenged with tachyzoites (TZ); only immunized (I); control group (C). After parturition, milk samples were collected for 3 weeks and then rats were sacrificed and the tissues and milk samples were researched for T. gondii parasite load determined by the quantitative PCR (qPCR). It was verified that the immunization with irradiated tachyzoites of T. gondii induced the reduction of parasitic load in muscle samples in rats challenged by bradyzoites and oocysts, although not enabled the development of sterile immunity. The detection of parasite DNA in milk was found throughout the lactation period, from immunized and non-immunized rats, however no differences were found in the parasite load caused by immunization.

One minute ultraviolet exposure inhibits Toxoplasma gondii tachyzoite replication and cyst conversion without diminishing host humoral-mediated immune response.

We developed a protocol to inactivate Toxoplasma gondii (T. gondii) tachyzoites employing 1 min of ultraviolet (UV) exposure. We show that this treatment completely inhibited parasite replication and cyst formation in vitro and in vivo but did not affect the induction of a robust IgG response in mice. We propose that our protocol can be used to study the contribution of the humoral immune response to rodent behavioral alterations following T. gondii infection.

Immunization of Wistar female rats with 255-Gy-irradiated Toxoplasma gondii: preventing parasite load and maternofoetal transmission.

Toxoplasmosis, caused by an obligate intracellular protozoan parasite, Toxoplasma gondii, is an worldwide parasitic disease, with significant importance for animal production and considerable impact to the public health. This study was aimed to evaluate the dynamic of the distribution of T.gondii in tissues of female Wistar rats and their puppies tissues, after the immunization by oral rote with irradiated tachyzoites. One week after pregnancy confirmation, rats was challenged by gavage with T. gondii bradyzoites, oocysts or tachyzoites of T. gondii. Forty-eight pregnant rats were grouped as follow: immunized and challenged with bradyzoites (BZ*); non-immunized and challenged with bradyzoites (BZ); immunized and challenged with oocysts (OC*); non-immunized and challenged with oocysts (OC); immunized and challenged with tachyzoites (TZ*); non-immunized and challenged with tachyzoites (TZ); only immunized (I); control group (C). After parturition the rats were sacrificed and the tissues were researched for the DNA of T. gondii by polymerase chain reaction (PCR) and the parasite load determined by the quantitative PCR (qPCR). It was verified that the immunization with irradiated tachyzoites of T. gondii induced the reduction of parasitic load in most organs analyzed, although not prevent the establishment of infection with the parasite. And also, the immunization showed a favorable effect on the birth rate and litter size.

Evaluation of the adjuvant effect of pidotimod on the immune protection induced by UV-attenuated Toxoplasma gondii in mouse models.

The current anti-Toxoplasma gondii drugs have many shortcomings and effective vaccines against T. gondii may contribute to the control of this pathogen. Pidotimod is a synthetic substance capable of stimulating both cellular and humoral immunity. To investigate the possible adjuvant effect of pidotimod on the immune response to T. gondii in Kunming mice induced by ultraviolet-attenuated T. gondii (UV-T.g), in this study, mice were immunized intraperitoneal (i.p.) with UV-T.g or UV-T.g co-administered with pidotimod (UV-T.g + PT). After infection or challenge by i.p. injection of 10(2) RH tachyzoites, the animal survival rate, parasite burden in peritoneal lavage fluids, liver histopathology, the level of serum anti-toxoplasma IgG antibody, and the mRNA expressions of IL-2, IFN-γ, and TNF-α from spleen analyzed using real-time PCR, were compared among different groups. The results showed that, compared with infected controls, infected mice treated with pidotimod had significantly increased survival rate and extended survival time, decreased parasite burden, improved liver histopathology, increased level of anti-toxoplasma IgG antibody, and increased mRNA expressions of Th1-type cytokine (IL-2, IFN-γ, and TNF-α) (P < 0.01), while mice vaccinated with UV-T.g and then challenged had even significantly increased survival rate and extended survival time, decreased parasite burden, improved liver histopathology, and increased mRNA expressions of Th1-type cytokines (IL-2, IFN-γ, and TNF-α) (P < 0.01); furthermore, vaccinated mice co-administered with pidotimod had even more lower parasite burden, milder liver histopathology, and higher levels of Th1-type cytokine and anti-toxoplasma IgG antibody (P < 0.01). Our data demonstrated that pidotimod in vivo could promote strong and specific humoral and cellular immune response to T. gondii challenge infection when co-administered with UV-attenuated T. gondii. It suggests that pidotimod may have the potential to be used as an effective vaccine adjuvant.

Determining UV inactivation of Toxoplasma gondii oocysts by using cell culture and a mouse bioassay.

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-log(10) inactivation is achieved with 4 mJ/cm(2) UV and 10 mJ/cm(2) low-pressure UV, respectively. TOP assay results, but not RT-qPCR results, correlate well with bioassay results. In conclusion, a 3-log(10) inactivation of T. gondii oocysts is achieved by 10-mJ/cm(2) low-pressure UV, and the in vitro TOP assay is a promising alternative to the mouse bioassay.

Radiofrequency-induced thermal inactivation of Toxoplasma gondii oocysts in water.

Toxoplasma gondii, a ubiquitous parasitic protozoan, is emerging as an aquatic biological pollutant. Infections can result from drinking water contaminated with environmentally resistant oocysts. However, recommendations regarding water treatment for oocyst inactivation have not been established. In this study, the physical method of radiofrequency (RF) power was evaluated for its ability to inactivate T. gondii oocysts in water. Oocysts were exposed to various RF energy levels to induce 50, 55, 60, 70 and 80 degrees C temperatures maintained for 1 min. Post-treatment oocyst viability was determined by mouse bioassay with serology, immunohistochemistry and in vitro parasite isolation to confirm T. gondii infections in mice. None of the mice inoculated with oocysts treated with RF-induced temperatures of > or =60 degrees C in an initial experiment became infected; however, there was incomplete oocyst activation in subsequent experiments conducted under similar conditions. These results indicate that T. gondii oocysts may not always be inactivated when exposed to a minimum of 60 degrees C for 1 min. The impact of factors such as water heating time, cooling time and the volume of water treated must be considered when evaluating the efficacy of RF power for oocyst inactivation.

Evaluation of the adjuvant properties of Astragalus membranaceus and Scutellaria baicalensis GEORGI in the immune protection induced by UV-attenuated Toxoplasma gondii in mouse models.

Human vaccines are not available and current anti-toxoplasma treatment is disappointing. To investigate the possible adjuvant effect of aqueous extracts obtained from medicinal herbs of Astragalus membranaceus (Am) and Scutellaria baicalensis GEORGI (Sb) on the immune response to Toxoplasma gondii in the mouse models induced by ultraviolet (UV)-attenuated T. gondii, this paper studies the possible vaccination strategies to help combat infections with Toxoplasma and looking towards developing new vaccine and approaches. We used UV-attenuated T. gondii (UV-T.g) of RH strain as a vaccine and the extracts of Am (AmE) and Sb (SbE) as adjuvant. Mice were infected by intraperitoneal (i.p.) injection of 10(2) RH tachyzoites alone (infected controls), infected and treated with AmE (T.g+AmE) and SbE (T.g+SbE), respectively; and mice immunized i.p. with UV-T.g alone, UV-T.g co-administrated with AmE (UV-T.g+AmE) or SbE (UV-T.g+SbE), and then challenged with T.g, respectively. The animal survival time, parasite burden in peritoneal lavage fluids, liver histopathological analysis, and levels of serum antibodies among the groups were compared after either infection or challenge. The results showed that, compared to infected controls, infected mice treated with AmE or SbE, or vaccinated mice and then challenged, had significantly prolonged survival time, decreased parasite burden, improved liver histopathological score, and increased Th1-type cellular immune response; furthermore, vaccinated mice co-administrated with AmE or SbE had even longer survival, lower parasite burden, lower liver histopathological score, and higher Th1 response after challenge. Our data demonstrated that the protective immunity of UV-attenuated T. gondii could be markedly enhanced by AmE or SbE co-administration, which suggests that both AmE and SbE may have the potential to be used as effective vaccine adjuvant.

Methods for inactivation of Toxoplasma gondii cysts in meat and tissues of experimentally infected sheep.

This study utilized infectivity bioassays in cats and mice to assess the efficacy of inactivation of Toxoplasma gondii cysts in experimentally infected sheep meat and tissues subjected to chilling, freezing, heating, microwave cooking, and gamma ray irradiation. Heating at 60 degrees C or 100 degrees C for 10 minutes, freezing at either -10 degrees C for 3 days or -20 degrees C for 2 days, or irradiation at doses of 75 or 100 krad was sufficient to kill tissue cysts. Meanwhile, neither cooking in a microwave nor chilling at 5 degrees C for 5 days was sufficient to kill tissue cysts.

Effects of ozone and ultraviolet radiation treatments on the infectivity of Toxoplasma gondii oocysts.

Clinical toxoplasmosis in humans has been epidemiologically linked to the consumption of drinking water contaminated by Toxoplasma gondii oocysts. We evaluated killing of T. gondii oocysts after ultraviolet (UV) or ozone treatments by bioassay in mice and/or cell culture. A 4-log inactivation of the oocyst/sporozoite infectivity was obtained for UV fluences >20 mJ cm(-2). In contrast, oocysts were not inactivated by ozone with an exposure (Ct) up to 9.4 mg min l (-1) in water at 20 degrees C. In conclusion, UV treatment can be an effective disinfection method to inactivate T. gondii oocysts in drinking water, but ozone did not show promise in this research.