Toxoplasmosis - a waterborne zoonosis

Transmission of toxoplasmosis (Toxoplasma gondii) by foods

Protozoan foodborne diseases are generally underrecognized. Toxoplasma gondii is the causative agent of toxoplasmosis, one of the most prevalent parasitic infections to humans and domestic animals. The most likely source of T. gondii occurring through food is the consumption of raw or undercooked meat contaminated with tissue cysts. Sporulated T. gondii oocysts, from the feces of infected cats, present in the environment are a potential source of infection. The ingestion of water contaminated with oocysts and the eating of unwashed raw vegetables or fruits were identified as an important risk factor in most epidemiological studies. This review presents information and data to show the importance of T. gondii transmission by foods.

Sero-prevalence of latent Toxoplasma gondii infection among HIV-infected and HIV-uninfected people in Addis Ababa, Ethiopia: A comparative cross-sectional study

Background

Toxoplasmosis in immuno-compromised hosts manifests primarily as a life threatening condition, toxoplasmic encephalitis. However, there is scarce information about the magnitude of Toxoplasma gondii infection among HIV-infected people in Ethiopia. This study was, therefore, conducted to determine the sero-prevalence of T. gondii infection among HIV-infected and HIV-uninfected subjects.

Findings

Sera were collected from people with and without HIV infection for the purpose of studying hepatitis B virus (HBV) at St. Paul Hospital, Addis Ababa, Ethiopia from 24 January 2007 to 15 February 2007. Among these sera, the first 330 consecutive sera, 165 from each HIV sero-group, were selected and tested for anti-T. gondii IgG antibodies using Enzyme Linked Immunosorbent Assay. The seroprevalence of Toxoplasma infection was assessed against socio-demographic characteristics, HIV and HBV serostatus and HBV-related risk factors. The overall sero-prevalence of latent T. gondii infection among the study subjects was 90.0%. Toxoplasma infection was observed with respective prevalence of 93.3% and 86.7% among HIV-infected and HIV-uninfected people. Though Toxoplasma infection seems to be influenced by age, gender and HIV serostatus, only HBV serostatus was significantly associated (OR 2.71, CI 1.12 to 6.57) in multivariate logistic regression analysis.

Conclusion

The seroprevalence of latent T. gondii infection is high and similar by HIV status. Educating people to prevent acquisition of new Toxoplasma infection and minimizing the risk of disease manifestations among HIV-Toxoplasma co-infected individuals is important.

Moving towards an integrated approach to molecular detection and identification ofToxoplasma gondii

The development of simple, sensitive and rapid methods for the detection and identification ofToxoplasma gondiiis important for the diagnosis and epidemiological studies of the zoonotic disease toxoplasmosis. In the past 2 decades, molecular methods based on a variety of genetic markers have been developed, each with its advantages and limitations. The application of these methods has generated invaluable information to enhance our understanding of the epidemiology, population genetics and phylogeny ofT. gondii. However, since most studies focused solely on the detection but not genetic characterization ofT. gondii, the information obtained was limited. In this review, we discuss some widely used molecular methods and propose an integrated approach for the detection and identification ofT. gondii, in order to generate maximum information for epidemiological, population and phylogenetic studies of this key pathogen.

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.

Infection with Toxoplasma gondii during pregnancy: seroepidemiological studies in Austria

Seropositivity among pregnant woman in Austria has decreased from 48% to 50% at the end of the 1970s to 35% in recent years. Despite this decrease, knowledge of possible sources and risk factors for Toxoplasma infection remains important. We reviewed seroepidemiological studies that were undertaken to assess the roles of undercooked meat and oocysts in cat faeces as potential sources of infection in pregnant women. Improved management and hygiene in pig herds raised in confinement have resulted in less contact of pigs with cats and a decrease of infected pigs within one decade from 14% in 1982 to 0.9% in 1992. In Austrian wild boar populations, however, seroprevalences remained essentially unchanged during the same decade (18% in 1983 and 19% in 1990-1993). Austrian sheep and goats are usually kept on small farms where cats abound and are predominantly seropositive (66% in sheep and 69% in goats). The seroprevalence in cats has decreased from approximately 81% in 1987 to 59% in 1996; presumably because of cats' increased consumption of processed food. Despite the decrease of infection in pregnant women via the cat-to-pig pathway, it may be offset by a recent concomitant increase in mutton consumption. Free-ranging chickens are a good indicator of the prevalence of T. gondii oocysts in the soil because chickens are ground feeders. Antibodies to T. gondii, as evaluated by the modified agglutination test, were found in 36% of chickens from 12 Austrian 'biofarms'. Because Austrians rarely consume raw pork, the fraction of human T. gondii infections associated with pig meat consumption is likely small. As meat consumption and lifestyle patterns change in Austria, the risk of human infection with T. gondii via different pathways needs re-evaluation and targeted educational efforts to control transmission.

Toxoplasmosis in immunocompromized patients

Infection with the cosmopolitan parasite Toxoplasma gondii is often associated with severe consequences and a high mortality rate in immunocompromized patients. Non-specific symptoms make diagnosis challenging. Monitoring of patients at risk is of value. We here present 8 cases of toxoplasmosis in immunocompromized patients with suggestions for preventive monitoring.

Communication between Toxoplasma gondii and its host: impact on parasite growth, development, immune evasion, and virulence

Toxoplasma gondii is an obligate intracellular protozoan parasite that can infect most warm-blooded animals and cause severe and life-threatening disease in developing fetuses and in immune-compromised patients. Although Toxoplasma was discovered over 100 years ago, we are only now beginning to appreciate the importance of the role that parasite modulation of its host has on parasite growth, bradyzoite development, immune evasion, and virulence. The goal of this review is to highlight these findings, to develop an integrated model for communication between Toxoplasma and its host, and to discuss new questions that arise out of these studies.

Isolation and characterization of viableToxoplasma gondiiisolates revealed possible high frequency of mixed infection in feral cats (Felis domesticus) from St Kitts, West Indies

Cats are essential in the epidemiology ofToxoplasma gondiibecause they are the only hosts that can excrete the environmentally resistant oocysts in nature. Samples of serum, feces, and tissues from feral cats from St Kitts, West Indies were examined forT. gondiiinfection. Antibodies toT. gondiiwere assayed by the modified agglutination test, and found in 71 of 96 (73·9%) of cats with titres of 1:10 in six, 1: 20 in six,1:40 in seven,1: 80 in three, 1: 160 in 10, 1:320 in 13, 1:640 in nine, and 1:1,280 or higher in 17. Tissues of 10 cats were bio-assayed in mice.Toxoplasma gondiiwas isolated from tissues of 7 cats; from hearts of 6, from tongue of 5, and brains of 3 cats. All 7 isolates were avirulent for mice.Toxoplasma gondiioocysts were not found in the feces of 51 cats. Genotyping of these 7T. gondiiisolates by 10 multi-locus PCR-RFLP markers, including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and an apicoplast marker, Apico, revealed 4 genotypes, including clonal Type II, Type III and 2 unique genotypes. Five of the 7 cats had infection with 2 genotypes, indicating high frequency of mixed infection in the cat population on the St Kitts island.

Association of the presence of residual anti-Toxoplasma gondii IgM in pregnant women and their respective family groups in Miracema, Northwest Rio de Janeiro, Brazil

The seroprevalence of toxoplasmosis in 832 pregnant women in Miracema, Rio de Janeiro, was determined and 75.1% (625) and 2.0% (17) were anti-Toxoplasma gondii IgG and IgM positive, respectively. Out of the 17 IgM positive pregnant women, only one had low avidity IgG corresponding to the acute phase of the infection. All the other women presented with high avidity IgG and also presented with residual IgM anti-T. gondii. Of this sample, 106 received home visits (this includes 11 family nuclei of pregnant women with residual IgM anti-T. gondii, 68 nuclei of only IgG positive pregnant women and 27 nuclei of pregnant women with no antibodies to anti-T. gondii), resulting in 267 individuals visited. Out of these 267 individuals, 21 were positive for IgG and IgM anti-T. gondii and were candidates for the IgG avidity test. All of them presented with high avidity IgG and residual IgM. Five of these IgM+ individuals were (5/238; 2.1%) relatives of IgM negative pregnant women. The other 16 (16/29; 55.2%) were relatives of IgM+ pregnant women who were positive for residual IgM anti-T. gondii. This association was statistically significant (p = 0.0000). The analysis presented herein raises questions regarding the presence of residual IgM anti-T. gondii such as genetic determinants or even constant antigenic stimuli for the same family cluster.

Detection of Toxoplasma gondii oocysts in water sample concentrates by real-time PCR

PCR techniques in combination with conventional parasite concentration procedures have potential for the sensitive and specific detection of Toxoplasma gondii oocysts in water. Three real-time PCR assays based on the B1 gene and a 529-bp repetitive element were analyzed for the detection of T. gondii tachyzoites and oocysts. Lower sensitivity and specificity were obtained with the B1 gene-based PCR than with the 529-bp repeat-based PCR. New procedures for the real-time PCR detection of T. gondii oocysts in concentrates of surface water were developed and tested in conjunction with a method for the direct extraction of inhibitor-free DNA from water. This technique detected as few as one oocyst seeded to 0.5 ml of packed pellets from water samples concentrated by Envirocheck filters. Thus, this real-time PCR may provide a detection method alternative to the traditional mouse assay and microscopy.

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.

Seroprevalence of Toxoplasma gondii in sheep and goats in Rahim Yar Khan (Punjab), Pakistan

Toxoplasmosis, an infection caused by Toxoplasma (T.) gondii Apicomplexa protozoan, is widespread in humans and other animal species, having already been reported in many countries and different climates. In Pakistan, no data is available on this aspect among food animals. This study was undertaken to determine the seroprevalence of T. gondii infection in sheep and goats. A total of 200 serum samples from sheep and goats, were collected from urban area of Rahim Yar Khan (Punjab), Pakistan and tested for Toxoplasmosis with a commercial latex agglutination kit (Eiken Chemical Co., Ltd. Japan). The overall seroprevalence of Toxoplasmosis was 19%. Goats had a significantly higher (p < 0.01) prevalence (25.4%) as compared to the sheep (11.2%); and higher (p < 0.01) in the female (24%) than in the males (19%) for both species. In the present study the male (both in sheep and goat) are found less seropositive T. gondii (OR = 0.23; 99% C.I. = 0.01, 1.81) as compared to female sheep and goat. The prevalence was significantly higher (p < 0.01) in adult sheep than younger animals. Among both the sheep and goats the group from 1-1.5 years are highly seropositive (OR = 1.75; 99% C.I. = 0.47, 6.51) as compared to the group less than one year of age followed by the 2-2.5 years age group (OR = 1.63; 99% C.I. = 0.50, 5.74) whereas group with more than 3 years of age least seropositive.

Comparison of indirect fluorescent antibody test and modified agglutination test for detecting Toxoplasma gondii immunoglobulin G antibodies in dog and cat

The present study describes the comparison between a modified agglutination test (MAT) and the indirect fluorescent antibody test (IFAT) for the detection of Toxoplasma specific IgG antibodies in dog and cat sera. MAT showed an "almost perfect" agreement with IFAT in detecting positive and negative results in cat sera, where as only a "substantial" agreement was observed in dog sera due to false negative results. Differences relative to sample dilution were recorded and serological titres obtained by MAT and IFAT are not directly comparable in cat and dog sera.

Toxoplasma gondii: sensitive and rapid detection of infection by loop-mediated isothermal amplification (LAMP) method

Loop-mediated isothermal amplification (LAMP) method amplifies DNA with high specificity, sensitivity and rapidity. In this study, we used a conserved sequence in the 200- to 300-fold repetitive 529 bp gene of Toxoplasma gondii to design primers for LAMP test. Detection limit of T. gondii LAMP assay with the primers is 1 pg/microL of T. gondii DNA, which was evaluated using 10-fold serially diluted DNA of cultured parasites. Furthermore, LAMP and conventional PCR methods were applied for amplification of the T. gondii DNA extracted from the lymph nodes taken from pigs which were suspected to be Toxoplasma infection. As a result, 76.9% (70/91) and 85.7% (78/91) of the samples were positive on PCR and LAMP analyzes, respectively. Therefore, the LAMP has a potential to be applied as an alternative molecular diagnostic tool for detection of T. gondii infection from veterinary samples. This is the first study, which applies the LAMP method to diagnose Toxoplasma from veterinary samples.

Risk factors for toxoplasmosis in pigs bred in Sicily, Southern Italy

The aim of the study was to determine the seroprevalence of Toxoplasma gondii infection in pigs raised and slaughtered in Sicily, Southern Italy, and to evaluate the risk factors associated with the infection. Samples were collected in seven slaughterhouses and on-site on 274 raising farms across Sicily, in the period from January 2006 until March 2007. For each sampled pig born and raised in Sicily, information was obtained on gender, age, origin, final destination of meat and farm management. Data on the farm included: farming type, presence of cats and dogs, rodent control by rodenticides, cleaning methods, water supply, altitude and herd size.T. gondii-specific antibodies were detected using a commercial Enzyme-Linked Immunosorbent Assay (Institut Pourquier, France).Antibodies against T. gondii were found in 16.3% of Sicilian pigs. The lowest seroprevalence, 7%, was found in the age group 5-7 months (market pig) and the highest, 19%, in the age group >24 months. Risk factors for seropositivity were: age 11-24 months compared to younger (OR 5.62; CI 1.52-20.8); farrow-to-finish farming type (OR 6.85; CI 1.87-25.01) compared to finishing and farrow-to-breed type; less than 50 pigs on the farm (OR 6.8; CI 1.76-26.2); no use of rodenticides (OR 2.71; CI 1.10-6.64), use of water coming from private sources (especially wells; OR 2.8; CI 1.03-7.72).Pigs raised in Sicily shows a high prevalence of antibodies against T. gondii. Pre-harvesting interventions to lower the risk of locally produced meat consumption for consumers should point as soon as possible to increase hygienic condition on the farm, by carefully removing waste with automatic cleaning and reducing biohazard by rodent control. Consumers must receive information on the correct handling and cooking locally produced pork meat derivatives.

Prey choice and habitat use drive sea otter pathogen exposure in a resource-limited coastal system

The processes promoting disease in wild animal populations are highly complex, yet identifying these processes is critically important for conservation when disease is limiting a population. By combining field studies with epidemiologic tools, we evaluated the relationship between key factors impeding southern sea otter (Enhydra lutris nereis) population growth: disease and resource limitation. This threatened population has struggled to recover despite protection, so we followed radio-tagged sea otters and evaluated infection with 2 disease-causing protozoal pathogens, Toxoplasma gondii and Sarcocystis neurona, to reveal risks that increased the likelihood of pathogen exposure. We identified patterns of pathogen infection that are linked to individual animal behavior, prey choice, and habitat use. We detected a high-risk spatial cluster of S. neurona infections in otters with home ranges in southern Monterey Bay and a coastal segment near San Simeon and Cambria where otters had high levels of infection with T. gondii. We found that otters feeding on abalone, which is the preferred prey in a resource-abundant marine ecosystem, had a very low risk of infection with either pathogen, whereas otters consuming small marine snails were more likely to be infected with T. gondii. Individual dietary specialization in sea otters is an adaptive mechanism for coping with limited food resources along central coastal California. High levels of infection with protozoal pathogens may be an adverse consequence of dietary specialization in this threatened species, with both depleted resources and disease working synergistically to limit recovery.

Structural insights into microneme protein assembly reveal a new mode of EGF domain recognition

The obligate intracellular parasite Toxoplasma gondii, a member of the phylum Apicomplexa that includes Plasmodium spp., is one of the most widespread parasites and the causative agent of toxoplasmosis. Adhesive complexes composed of microneme proteins (MICs) are secreted onto the parasite surface from intracellular stores and fulfil crucial roles in host-cell recognition, attachment and penetration. Here, we report the high-resolution solution structure of a complex between two crucial MICs, TgMIC6 and TgMIC1. Furthermore, we identify two analogous interaction sites within separate epidermal growth factor-like (EGF) domains of TgMIC6-EGF2 and EGF3-and confirm that both interactions are functional for the recognition of host cell receptor in the parasite, using immunofluorescence and invasion assays. The nature of this new mode of recognition of the EGF domain and its abundance in apicomplexan surface proteins suggest a more generalized means of constructing functional assemblies by using EGF domains with highly specific receptor-binding properties.

Frequency and risk factors for toxoplasmosis in ovines of various regions of the State of Colima, Mexico

Infection of ewes by Toxoplasma gondii may induce abortions, thus it has consequences for sheep production. Colima, Western State of Mexico, has favourable climatic conditions for transmission and both domestic and wild cats live there. The aim of this study was to determine the frequency of specific antibodies in sheep from the coast, a mountain, and a hill of Colima. Serum samples from 351 sheep were tested by a previously standardized indirect ELISA. The frequency of infection was estimated and the farm location and flock size, as well as the animals' age and sex were analysed as risk factors for toxoplasmosis. The frequency of antibodies depended on the altitude, being higher at sea level than at 1200 metres above sea level (OR=3.77, 95% CI=1.79-7.94, P<0.0001), and the size of the flock, being higher in the large ones (OR=2.23, 95% CI=1.35-3.71, P=0.002). Older animals were more frequently positive and with a stronger response than young ones (OR=1.77, 95% CI=1.07-2.93, P=0.016). No differences were observed between male and female sheep. In conclusion, toxoplasmosis is present in sheep of Colima with variations related to altitude, flock size and age.

Control of the risk of human toxoplasmosis transmitted by meat

One-third of the human world population is infected with the protozoan parasite Toxoplasma gondii. Recent calculations of the disease burden of toxoplasmosis rank this foodborne disease at the same level as salmonellosis or campylobacteriosis. The high disease burden in combination with disappointing results of the currently available treatment options have led to a plea for more effective prevention. In this review we describe Toxoplasma as a hazard associated with the consumption of undercooked meat or meat products and provide an analysis of the various options to control the risk of human toxoplasmosis via this source. Monitoring and surveillance programs may be implemented for pre-harvest control of Toxoplasma infection of farm animals, with the reduction of environmental oocyst load as the most important milestone. Alternatively, Toxoplasma safe meat can be obtained through simple post-harvest decontamination procedures, whereby freezing the meat may currently be the best option, although new technologies using irradiation or high-pressure treatment may offer promising alternatives. Influence of culture, religion and food handling customs may predispose a certain type of meat as an important source of infection, indicating that prevention needs to be tailored according to social habits in different regions in the world. The rationale for more stringent control measures to prevent toxoplasmosis both from disease and economic points of view is emphasized.

Epidemiological and genetic characterization of Toxoplasma gondii in urban pigeons from the area of Lisbon (Portugal)

Circumstantial evidence suggests that birds may be a good indicator of soil contamination, since they feed from the ground. Therefore a study was conducted to assess the prevalence of Toxoplasma gondii in urban pigeons (Columba livia) from different areas of the city of Lisbon and to genetically characterize T. gondii strains isolated from infected animals, in order to assess circulating genotypes. Sera from 695 pigeons captured at 33 different localities of the city of Lisbon were assayed by the direct agglutination test (DAT) showing a 4.6% prevalence. One third of flocks sampled revealed to be infected with T. gondii, with prevalence ranging between 5% and 62.5%. T. gondii DNA could be characterized directly from brain tissue from 12 of 23 seropositive pigeons. Microsatellite typing revealed that 9 strains belonged to type II, 2 were type III and one was type I. No recombinant or atypical genotypes were found. Attempts to recover viable T. gondii strains through bioassay in mice resulted in the isolation of 9 strains.

A qualitative assessment of Toxoplasma gondii risk in ready-to-eat smallgoods processing

Toxoplasma gondii is one of the most common parasitic infections of humans and other warm-blooded animals. In most adults, it does not cause serious illness, but severe disease may result from infection in fetuses and immunocompromised people. Consumption of raw or undercooked meats has consistently been identified as an important source of exposure to T. gondii. Several studies indicate the potential failure to inactivate T. gondii in the processes of cured meat products, This article presents a qualitative risk-based assessment of the processing of ready-to-eat smallgoods, which include cooked or uncooked fermented meat, pâté, dried meat, slow cured meat, luncheon meat, and cooked muscle meat including ham and roast beef. The raw meat ingredients are rated with respect to their likelihood of containing T. gondii cysts and an adjustment is made based on whether all the meat from a particular source is frozen. Next, the effectiveness of common processing steps to inactivate T. gondii cysts is assessed, including addition of spices, nitrates, nitrites and salt, use of fermentation, smoking and heat treatment, and the time and temperature during maturation. It is concluded that processing steps that may be effective in the inactivation of T. gondii cysts include freezing, heat treatment, and cooking, and the interaction between salt concentration, maturation time, and temperature. The assessment is illustrated using a Microsoft Excel-based software tool that was developed to facilitate the easy assessment of four hypothetical smallgoods products.

Toll-like receptors and their role in host resistance to Toxoplasma gondii

Toxoplasma gondii and other apicomplexan parasites are widely distributed obligate intracellular protozoa. A critical host mediator produced in response to T. gondii infection is IL-12. This cytokine is synthesized by dendritic cells, macrophages and neutrophils and plays a pivotal role in the production of IFN-gamma, which in turn activates anti-microbial effector cells. In the past several years, many of the receptors and signaling pathways that link pathogen detection to induction of IL-12 have been identified and characterized. Among these receptors the Toll-like receptor (TLR) family can recognize all classes of pathogens and induce different types of immune responses. In the following review, I summarize the evidence for specific TLR function in host resistance to T. gondii.

The role of rodents and shrews in the transmission of Toxoplasma gondii to pigs

Inadequate rodent control is considered to play a role in Toxoplasma gondii infection of pigs. This issue was addressed in the current study by combining a 4-month rodent control campaign and a 7-month longitudinal analysis of T. gondii seroprevalence in slaughter pigs. Three organic pig farms with known rodent infestation were included in the study. On these farms, presence of T. gondii in trapped rodents was evaluated by real-time PCR. All rodent species and shrews investigated had T. gondii DNA in brain or heart tissue. Prevalence was 10.3% in Rattus norvegicus, 6.5% in Mus musculus, 14.3% in Apodemus sylvaticus and 13.6% in Crocidura russula. Initial T. gondii seroprevalence in the slaughter pigs ranged between 8% and 17% and dropped on the three farms during the rodent control campaign to 0-10%, respectively. After 4 months of rodent control, T. gondii infection was absent from pigs from two of the three farms investigated and appeared again in one of those two farms after the rodent control campaign had stopped. This study emphasizes the role of rodents and shrews in the transmission of T. gondii to pigs and the importance of rodent control towards production of T. gondii-free pig meat.

AJ, Hiramoto RM, Terentowicz HCK, Andrade Júnior HFD. Quantitative toxoplasma gondii oocyst detection by a modified Kato Katz test using Kinyoun staining (KKK) in ME49 strain experimentally infected cats

We detected Toxoplasma gondii oocysts in feces of experimentally infected cats, using a Kato Katz approach with subsequent Kinyoun staining. Animals serologically negative to T. gondii were infected orally with 5x10² mice brain cysts of ME49 strain. Feces were collected daily from the 3rd to the 30th day after challenge. Oocysts were detected by qualitative sugar flotation and the quantitative modified Kato Katz stained by Kinyoun (KKK). In the experimentally infected cats, oocysts were detected from the 7th to 15th day through sugar flotation technique, but oocysts were found in KKK from the 6th to 16th day, being sensitive for a larger period, with permanent documentation. The peak of oocysts excretion occurred between the 8th to 11th days after challenge, before any serological positive result. KKK could be used in the screening and quantification of oocysts excretion in feces of suspected animals, with reduced handling of infective material, decreasing the possibility of environmental and operator contamination.

Seroepidemiology of infection with Toxoplasma gondii in waste pickers and waste workers in Durango, Mexico

Municipal waste is a potential source of infection for Toxoplasma gondii as it may contain contaminated meat with parasite tissue cysts and cat excrement with parasite oocysts. Therefore, we sought to determine the prevalence of T. gondii infection and associated characteristics in two populations exposed to municipal solid waste in Durango, Mexico. Ninety waste pickers and 83 waste workers of Durango City, Mexico were examined for T. gondii infection. They were tested for anti-T. gondii IgG and IgM antibodies using enzyme-linked immunoassays. In addition, socio-demographic and behavioural characteristics from each participant were obtained. Nineteen (21.1%) of the 90 waste pickers and seven (8.4%) of the 83 waste workers were positive for anti-T. gondii IgG antibodies. The difference in prevalence among the groups was statistically significant (P =0.03). Waste pickers aged 31-50 years showed a significantly higher prevalence (40.9%) than waste workers of the same age group (2.9%, P < 0.001). Anti-T. gondii IgM antibodies were found in two (2.2%) of the waste pickers but in none of the waste workers. The seroprevalence of T. gondii was significantly higher in workers of the waste transfer station (25.0%) than in drivers or helpers of waste vehicles (2.5%) (P =0.03). Multivariate analysis showed that T. gondii infection was associated with consuming food found in the garbage [adjusted odds ratio (OR) = 4.4; 95% confidence interval (CI) 1.6-11.8] and with lack of education (adjusted OR = 3.2; 95% CI 1.1-8.8). From this study, we conclude: (i) waste pickers may represent a risk group for T. gondii infection; (ii) lack of education might be a contributing factor for T. gondii infection; (iii) the higher the exposure to garbage, the higher the seroprevalence of T. gondii infection; (iv) Eating food products from the garbage may represent an important route for T. gondii infection.

Frequency ofToxoplasma gondiiinfection in sheep from a tropical zone of Mexico and temporal analysis of the humoral response changes

An indirect ELISA and an immunoblot were standardized to detect anti-Toxoplasma gondiiantibodies in sheep, and were compared with a commercial ELISA as reference. Sensitivity was 92·0 and 96·0%, and specificity 88·0 and 75·0%, respectively. Then the serum samples of 103 sheep on a ranch located in the Eastern region of Mexico were analysed. A frequency ranging from 77 to 84% was observed, with a heterogeneous pattern among the animals by immunoblotting. Ten months later 56 sheep were sampled and tested again. Six animals became negative while 1 case was negative the first time and strongly positive 10 months later. Considering this to be a new case we calculated an incidence rate of 2·1% (CI95%0·6–4·8%). IgG avidity ELISA was performed on 36 positive samples, 33 being of high-avidity at both times; slight increases in 2 samples and conservation of low-avidity in 1 sheep were also observed. Higher prevalence rates of toxoplasmosis in a moist warm compared to a cold atmosphere was attributed to the long viability ofT. gondiioocysts. This may explain the high frequency ofT. gondiiin this region, which apparently has favourable climatic conditions for the transmission of this protozoan, besides the presence of both domestic and wild cats.

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.