Production of the main surface antigen of Toxoplasma gondii in tobacco leaves and analysis of its antigenicity and immunogenicity

We adapted a previously described Agrobacterium-mediated transient expression system to test the expression level of three constructs carrying the surface antigen 1 (SAG1) of Toxoplasma gondii. Two constructs were based in a Potato virus X (PVX) amplicon. In one of them, the PVX movement protein genes were replaced by the sag1 gene. In the other, the sag1 gene was placed under the control of an additional coat protein subgenomic promoter. In the third construct, the sag1 gene was fused to an apoplastic peptide signal under the CaMV 35S promoter. Western blot analysis of leaf extracts infiltrated with each construct revealed a protein of 35 kDa. SAG1 accumulation in leaves ranged from 0.1 to 0.06% of total soluble protein (equivalent to 10 microg and 6 microg of SAG1 per gram of fresh leaf tissue, respectively). Three of five human seropositive samples reacted with tobacco-expressed SAG1 in Western blot analysis. The C3H mice were immunized with SAG-expressing leaf extracts and perorally challenged with a nonlethal dose of the T. gondii Me49 strain. Mice vaccinated with SAG1 showed significantly lower brain cyst burdens compared to those from the control group. Immunization with SAG1-expressing leaves elicited a specific humoral response with predominant participation of type IgG2a. In conclusion, a functional SAG1 version could be transiently expressed in tobacco leaves.

Toxoplasmosis - a waterborne zoonosis

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, water-borne 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 by marine mammals in the USA provide reasons to question this view. The present paper reviews information on the biology of oocyst-induced infections of T. gondii in humans and animals and examines possible importance of transmission by water.

Toxoplasmosis in pregnancy

Pregnant women who acquire infection from Toxoplasma gondii usually remain asymptomatic, although they can still transmit the infection to their fetuses with severe consequences. Given the asymptomatic nature of most Toxoplasma infections, primary prevention in pregnant women may lower the risk of congenital toxoplasmosis. Both consumption of undercooked meat and unprotected contact with soil are independent risk factors for T. gondii seroconversion during pregnancy, while contact with cat litter may pose a risk in certain situations. However, many pregnant women lack knowledge of these risk factors. This article reviews toxoplasmosis infection in pregnancy, with an emphasis on risk factors and appropriate counseling of pregnant women.

Toxoplasmosis prevention knowledge among pregnant women in Minnesota

Congenital toxoplasmosis causes blindness and mental retardation. In the United States, up to 85% of women of childbearing age are susceptible to infection with the Toxoplasma gondii parasite, which causes toxoplasmosis. Up to 50% of T gondii infections are transmitted by ingesting undercooked meat, making toxoplasmosis one of the most clinically significant food-borne diseases in pregnant women. This article describes the results of a 2003 survey of pregnant Minnesota women through which we determined their knowledge of toxoplasmosis and ways to prevent it during pregnancy. Fewer than half of respondents had heard about toxoplasmosis, although higher education levels were significantly associated with knowledge about the disease.

A combination of antigenic regions of Toxoplasma gondii microneme proteins induces protective immunity against oral infection with parasite cysts

Infection with Toxoplasma gondii causes morbidity and mortality in congenitally infected and immunocompromised individuals. Both humoral and cell-mediated immunity are involved in host resistance to invasion of the parasite. Among putative vaccine candidates, the T. gondii microneme proteins appear to be promising, because they are responsible for the invasion process. The present work focused on studying the immunogenicity of microneme proteins in infected individuals and in a mouse model of chronic toxoplasmosis. We identified 5 distinct antigenic regions within MIC2, MIC4, MIC2-associated protein, and apical membrane antigen 1 gene products, which were recognized by (1) T cells from both adults with acquired infection and children with congenital infection and (2) antibodies from all patients. Finally, we demonstrated that DNA immunization with microneme fragments elicited effective protection in mice (84% reduction in brain-cyst burden), suggesting that a combination of these antigenic regions should be considered in the design of potential vaccines against toxoplasmosis.

Seroprevalence and risk factors for Toxoplasma infection in pregnant women in Jordan

To determine the seroprevalence and risk factors for toxoplasmosis among pregnant women in Jordan, sera from 280 pregnant women were tested during the period January 2000-May 2001. Blood samples were taken after the first antenatal visit. Serum was separated and tested for Toxoplasma IgG antibodies using an indirect fluorescent antibody. Seroprevalence gradually increased with age, from 31.7% at 15-24 years to 90.0% at 35-45 years. Regression analysis showed that seroprevalence of toxoplasmosis is positively correlated with age and residence. Consumption of undercooked meat and contact with soil were significant risk factors.

Interleukin-15-deficient mice develop protective immunity to Toxoplasma gondii

Previous studies have suggested an important role for interleukin-15 (IL-15) in resistance to and memory for Toxoplasma gondii infection. The studies presented here reveal that IL-15 is not required for infection-induced expansion of NK or CD8+ T cells. Furthermore, IL-15-/- mice develop long-term protective immunity to this pathogen.

[Evaluation of toxoplasmosis seroprevalence among 2416 women of childbearing age followed at the Pasteur Institute of New Caledonia]

Evaluation of Toxoplasmosis seroprevalence was conducted in 2416 women of childbearing age by Pasteur Institute of New-Caledonia. The estimated seroprevalence was 56.7%, significantly higher in the North-East part of the territory (79.1%), area characterized by strong precipitations, and in the Melanesian ethnic group (62.1%). The habits of this population could enhance contamination by ingestion of oocysts during childhood or adolescence, particularly in the North-East territory. Melanesian women living in the North-East and being not immunized against toxoplasmosis represent the population with the highest risk for Toxoplasma gondii infection.

CpG-containing ODN has a limited role in the protection against Toxoplasma gondii

Bacterial DNA containing immunostimulatory motifs (CpG) induces the development of a T(H1) immune response. Since protection against Toxoplasma gondii is correlated with this type of response, the aim of this work was to determine if a synthetic oligodeoxynucleotide (ODN) containing CpG sequences could be useful as adjuvant for the induction of a long-lasting protective immune response against T. gondii. BALB/c mice immunized with a total soluble antigen of T. gondii (TSA2) mixed with ODN-containing CpG sequences developed a typical TH1 response, as determined by antibody isotypes and interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) production by spleen cells. However, they did not resist a challenge with the virulent RH strain of the parasite. Absence of protection paralleled with lower levels of IFN-gamma, when compared with mice vaccinated with the live tachyzoites of the attenuated ts.4 strain of the parasite, which resisted this challenge. Intraperitoneal injection of ODN alone to mice induced a high degree of resistance to a lethal challenge inoculated by the same route. Nevertheless, this nonspecific protection was transient. Thus, the use of ODN containing CpG motifs as adjuvant is of limited value for the induction of a protective immune response against T. gondii.

[Prevalence and public-health-aspects of toxoplasmosis]

Toxoplasmosis is one of the most common infectious diseases of man, which usually is not dangerous. Infection results from ingestion of cyst-containing meat products or by contact with oocyst-contaminated soil. Clinically relevant are (1) reactivation of latent infection in immunocompromised individuals or (2) primary infection during pregnancy with subsequent prenatal toxoplasmosis of the fetus. In Germany, law requires the prenatal infection to be reported to the Robert Koch-Institute. Since most Toxoplasma-infected children are asymptomatic at birth and later develop sequelae (retinochoroiditis) up to the age of 20 years, no valid epidemiological data are currently available for Germany. However, some studies indicate that seroprevalence correlates with age and that 26-54% of women of childbearing age have antibodies against Toxoplasma gondii; incidence rates during pregnancy have been calculated to be between 0.5 and 0.6%. Knowing the life cycle of Toxoplasma gondii will help to maintain preventive measures for seronegative pregnant women, children, and immunocompromised individuals.

Toxoplasma gondii antigen-pulsed-dendritic cell-derived exosomes induce a protective immune response against T. gondii infection

It was previously demonstrated that immunizing mice with spleen dendritic cells (DCs) that had been pulsed ex vivo with Toxoplasma gondii antigens triggers a systemic Th1-biased specific immune response and induces protection against infection. T. gondii can cause severe sequelae in the fetuses of mothers who acquire the infection during pregnancy, as well as life-threatening neuropathy in immunocompromised patients, in particular those with AIDS. Here, we investigate the efficacy of a novel cell-free vaccine composed of DC exosomes, which are secreted antigen-presenting vesicles that express functional major histocompatibility complex class I and II and T-cell-costimulatory molecules. They have already been shown to induce potent antitumor immune responses. We investigated the potential of DC2.4 cell line-derived exosomes to induce protective immunity against toxoplasmosis. Our data show that most adoptively transferred T. gondii-pulsed DC-derived exosomes were transferred to the spleen, elicited a strong systemic Th1-modulated Toxoplasma-specific immune response in vivo, and conferred good protection against infection. These findings support the possibility that DC-derived exosomes can be used for T. gondii immunoprophylaxis and for immunoprophylaxis against many other pathogens.

Toxoplasma gondii infection in patients with hematological malignancies

Toxoplasmosis is one of the most common parasitic infections in humans, but in most cases it does not cause serious illness; this protozoan can nevertheless cause devastating disease in immunocompromised hosts such as HIV-positive individuals. Only rarely is toxoplasmosis documented in hematological patients, and among them, those who undergo a transplant procedure are more frequently affected. In a retrospective multicenter survey, we collected data on six cases of toxoplasmosis in hematological patients. In the majority of cases, patients had undergone transplant procedures (five had undergone autologous or allogeneic transplantation). This complication needed special care in diagnosis, usually based on serology, neuroradiology, and PCR examination. However, in our experience the appropriate therapeutic approach was successful in the majority of cases.

Séroconversion toxoplasmique chez la femme enceinte

INTRODUCTION

Since 1992 France has been running a toxoplasmosis prevention program based on the serological detection of infections during pregnancy. In the absence of a consensus, the seroconversions discovered are managed in different ways, varying from one centre to another.

OBJECTIVE

To describe the habits of the specialised centres in France and propose means to reduce the heterogeneity.

METHODS

A survey using a questionnaire mailed to the centres of parasitology in France specialised in the management of toxoplasmosis seroconversion during pregnancy.

RESULTS

All the 30 centres surveyed replied. Five of them do not provide recommendations for treatment and were excluded from analysis. The attitudes of the 25 other centres varied greatly with regard to the indications for therapeutic abortion and amniocentesis, treatment protocols with pyrimethamine and sulfamides, as well as in the frequency of sonographical monitoring.

CONCLUSION

In the absence of National guidelines, the management of seroconversions discovered during the prenatal prevention of congenital toxoplasmosis program is left to the discretion of the specialised centre. This results in variations from one town to the next. This heterogeneity underlines the lack of knowledge on the most efficient and acceptable means of preventing and treating congenital toxoplasmosis. In order to improve this situation, the French parasitologists have launched a program of consensual meetings aimed at harmonising the treatment protocols and identifying the points that require further studies.

Toxoplasmosis-related knowledge and practices among pregnant women in the United States

Background: Infection with Toxoplasma gondii during pregnancy can lead to severe illness in the fetus. Many T. gondii infections are preventable by simple hygienic measures.

Methods: We surveyed pregnant women in the US to determine their knowledge about toxoplasmosis and their practices to prevent infection. Volunteer obstetricians selected to be demographically representative of the American College of Obstetricians and Gynecologists recruited the participants.

Results: Of 403 women responding to the survey, 48% indicated that they had heard or seen information about toxoplasmosis; however, only 7% were aware of being tested for the disease. Forty percent of responding women knew that toxoplasmosis is caused by an infection, but 21% thought that a poison causes it. The highest level of knowledge was about cats and T. gondii ; 61% responded that the organism is shed in the feces of infected cats and 60% responded that people could acquire toxoplasmosis by changing cat litter. There was a low level of knowledge about other risk factors; only 30% of the women were aware that T. gondii may be found in raw or undercooked meat. Nevertheless, a high percentage of women indicated that they do not eat undercooked meat during pregnancy and that they practice good hygienic measures such as washing their hands after handling raw meat, gardening or changing cat litter.

Conclusion: Except for the risk of transmission from cats, knowledge among pregnant women about toxoplasmosis is low. However, toxoplasmosis-preventive practices are generally good, suggesting that providers should continue to offer education about practices that help prevent foodborne diseases in general as well as information about preventing toxoplasmosis specifically.

MVA ROP2 vaccinia virus recombinant as a vaccine candidate for toxoplasmosis

Toxoplasma gondii is the aetiological agent of toxoplasmosis and is the most frequent and best known of the parasitic diseases. In the United States, a serological survey from the Third National Health and Nutrition Examination Survey found that an estimated 23% of adolescents and adults have laboratory evidence of infection with T. gondii. Although toxoplasmosis is asymptomatic or shows self-limited symptoms in adults, in pregnant women infections can cause severe health problems to the fetus if the parasites are transmitted. Also, in immunodeficient patients, chronic infection with T. gondii can reactivate and produce encephalitis, which is frequently lethal. In addition, in veterinary medicine, T. gondii infection is of economic importance due to abortion and neonatal loss in sheep and goats. Recently, the development of vaccines against toxoplasmosis has progressed considerably. The live attenuated S48 strain of Toxoplasma has been broadly used for veterinary purposes. DNA vaccines containing the full-length of SAG1/P30, ROP2 or ROP1 genes have proved to be a promising candidate to induce protection against toxoplasmosis. Viral vectors have proved to be the best candidates for vaccination in different diseases. A recombinant Herpes virus carrying the ROP2 gene is able to induce protective immunity in cats. In the present work we describe the potential of the MVA ROP2 recombinant vaccinia virus as a vaccine against toxoplasmosis. MVA ROP2 induces antibodies against the ROP2 protein in similar amount and types as the thermo-sensible strain ts-4 of T. gondii, which is able to fully protect mice against challenge with the virulent RH strain of T. gondii. Also, the life-span of mice is increased in MVA ROP2 vaccinated animals. We conclude that MVA ROP2 vaccine can possibly generate an immune response, which could be useful in protection against toxoplasmosis.

[Identification of risk factors for infection with Toxoplasma gondii in Serbia as a basis of a program for prevention of congenital toxoplasmosis]

BACKGROUND

Toxoplasmosis has long been known as a major cause of perinatal morbidity. Acute infection in pregnancy may lead to fetal infection and subsequent fetal loss or birth of a manifestly or latently infected infant. However, it is a preventable disease. In Europe, significant variations have been shown to occur not only between countries but also within a given country indicating local variations in the influence of epidemiological factors contributing to infection. Thus, many European countries have implemented prevention programs in measure with the respective estimated risk of congenital toxoplasmosis. Since in view of its cost, a general screening-in-pregnancy program is at present not an option in Serbia & Montenegro, insight into the risk factors of particular local significance may therefore improve the quality of and the compliance with the hygienic and dietetic advice given to pregnant women as a preventive measure, as well as identify the particular subpopulations at an increased risk of infection, who may then be selectively screened.

SUBJECTS AND METHODS

A retrospective study of risk factors for Toxoplasma gondii infection based on serological and epidemiological data (questionnaire) was performed in a series of 2936 women aged 15-49 years from throughout Serbia tested in our laboratory between 1988 and 1997. Inclusion criteria included availability of serological and epidemiological data (as specified below). Specific anti-Toxoplasma antibodies were detected by the reference Sabin-Feldman dye test as modified by Desmonts into the lysis test. The questionnaire included questions on age (stratified into five-year groups), degree of education (modalities: grade school, secondary or university level), and community of residence (urban/suburban), as well as on life-style habits pertaining to infection transmission risk factors: consumption of undercooked meat, exposure to soil, and exposure to cats (pet cat ownership). In addition, the year of entry into the study was taken as a variable per se.

STATISTICS

The difference in the rates of infection between groups was evaluated by the chi-square test (chi 2). Logistic regression (univariant and multivariant approaches) was used to analyze the association between Toxoplasma infection and the specific demographic and epidemiological factors.

RESULTS

The overall prevalence of infection was 69%, but with very wide variations both over time (decreasing from 86% in 1988 to 39% in 1997) and region (40-90%). The risk of infection increased from the south to the north (RR = 0.97, CI = 0.94-0.98). Within Belgrade, the risk was higher in urban than in suburban zones (RR = 0.79, CI = 0.64-0.93). The single infection transmission factor that was shown to be a predictor of infection in the whole study group was undercooked meat consumption (RR = 1.6, CI = 1.2-2.1), while exposure to soil was a predictor only in women aged 15-19 (RR = 10.3, CI = 2.7-38.6). Owing pet cats had no influence. While T. gondii infection was not associated with pathological pregnancies (p = 0.51) in the whole study population, it was significantly associated with pathological pregnancies in women exposed to both undercooked meat consumption (p = 0.009) and in those aged 15-19 in contact with soil (p = 0.022), as well as in women residing in highly urban communities (p = 0.048).

CONCLUSION

The dramatic decrease in the prevalence of T. gondii infection over the nineties resulted in a rising proportion of women exposed to infection in pregnancy and consequently in an increased risk of congenital toxoplasmosis. Since the financial status of the country's health system does not allow for a general screening-in-pregnancy program, we propose, based on the above data, health education of all pregnant women in combination with serological testing of those exposed to predictors of infection as an epidemiologically sound and financially sustainable alternative.

SAG1 Is a Host-Targeted Antigen for Protection against Toxoplasma gondii Infection

We previously reported that SAG1 transgenic (tg) mice have an elevated susceptibility resulting from their inability to elicit strong Th1-based protection against Toxoplasma gondii infection. Here, we demonstrate that SAG1 tg mice were protected against T. gondii infection, characterized by a decline in IFN-gamma levels, following administration of a lethal dose of T. gondii. Moreover, immunization with T. gondii homogenate conferred protection and induced production of IgG, with IgG1 and IgG2a subclasses driven by Th2 and Th1 responses, respectively, in both SAG1 tg and wild-type (wt) mice. IgG titers were significantly higher from day 10 after immunization in wt mice compared to those in SAG1 tg mice. There were no significant differences observed in levels of IgG1 in both groups. However, significantly lower IgG2a titers were measured in the sera from SAG1 tg mice on days 10, 15 and 20. IFN-gamma levels in sera were significantly lower in SAG1 tg mice compared to those in wt mice on day 20 after immunization. When challenged with a lethal dose of the Beverley strain of T. gondii, 80 and 100% survival rates were observed in SAG1 tg and wt mice, respectively, indicating that SAG1 tg mice were protected to a lesser extent from challenge due to the decrease in protective immunity. These results suggest that SAG1 plays a critical role in eliciting protection, hence a target antigen for the development of protective Th1-based responses against T. gondii infection in mice.

[Selected problems in laboratory diagnostics of Toxoplasma gondii infections]

The article presents chosen problems concerning laboratory recognition of Toxoplasma gondii infections.

[Cost analysis of toxoplasma infection control in pregnancy]

In Italy, the management of Toxoplasma infection screening in pregnant women is often unproductive and inefficient and generates a wide variability of costs. This study evaluated performance parameters in the screening management of a population of pregnant women, estimated its costs and compared them with the costs of a full application of Ministerial Documents of 1995 and 1998. We controlled until delivery 830 pregnant women who had done the first blood test between September 1st and December 31st 1997. The costs of direct and indirect testing were analysed using the Excel database and statistical software package. Of the 573 pregnant women defined 'susceptible' at the first test, only 240 (42%) did further blood tests during the II and III trimesters, 30% did no more tests and the remaining women adopted a heterogeneous behaviour. The mean cost of each screening was found to be euro 54.47/pregnancy and euro 60.05/pregnancy with a full application of the Ministerial Document of 1995. A full application of Ministerial Document of 1998, instead, would have involved a cost of euro 94.28/pregnancy for 5 tests, euro 111.40/pregnancy for 6 tests and euro 128.51 for 7 tests. The study shows that the management of toxoplasmosis screening during pregnancy needs greater attention to the prescription of tests, so that useless testing can be reduced and the efficacy of the screening improved, two important goals the Ministerial Documents were designed to achieve.

Toxoplasmosis in pregnancy is still an open subject

OBJECTIVE

To assess the consequences of a systematic screening for toxoplasma infection in pregnant women in a potentially high risk population.

METHODS

We have investigated all consecutive women with likely toxoplasma seroconversion in a referral center setting. Data were obtained from 68 women for whom an acute infection during pregnancy was considered likely or definite. They were all treated with antibiotics in the first instance and offered, if in the first or second trimester, amniocentesis for detection of vertical transmission (PCR and IFAT). Third trimester seroconversions and positive cases after amniocentesis were offered more aggressive antibiotic treatment.

RESULTS

Five fetuses/neonates (7%) were found to be infected. Four of them were diagnosed prenatally at amniocentesis, two women decided for termination of pregnancy, two were treated and gave birth to seronegative, normally developing children. One case was found postnatally, after a third trimester conversion; this developed into hydrocephalus with neurologic impairment.

DISCUSSION

Prenatal screening and antibiotic treatment of mothers infected with toxoplasmosis showed good feasibility in our infection-susceptible population. However, there were some weak points; for example, the high number of invasive procedures and the questionable prevention of mother to child transmission in the second to third trimester.