Toxoplasma gondii: transmission, diagnosis and prevention

Fatal outbreak of human toxoplasmosis along the Maroni River: epidemiological, clinical, and parasitological aspects

BACKGROUND

Well-documented outbreaks of human toxoplasmosis infection are infrequently reported. Here, we describe a community outbreak of multivisceral toxoplasmosis that occurred in Patam, a Surinamese village near the French Guianan border.

METHODS

From the end of December 2003 through the middle of January 2004, 5 adult patients in Patam, including 2 pregnant women, were initially hospitalized for multivisceral toxoplasmosis. A French-Surinamese epidemiological investigation was conducted in the village; inquiries and clinical examinations were performed, and blood and environmental samples were obtained. For all serologically confirmed cases of toxoplasmosis, molecular analysis and mouse inoculations were performed for diagnosis and genetic characterization of Toxoplasma gondii.

RESULTS

The hospitalized patients, who did not have any immunodeficiencies, presented with an infectious disease with multivisceral involvement. Serological examination confirmed acute toxoplasmosis. One adult died, and a neonate and a fetus with congenital toxoplasmosis also died. During the investigation, 4 additional acute cases of toxoplasmosis were diagnosed among the 33 villagers. Only 3 inhabitants had serological evidence of previous T. gondii infection. In total, we reported 11 cases of toxoplasmosis: 8 multivisceral cases in immunocompetent adults, resulting in 1 death; 2 cases of lethal congenital toxoplasmosis in a neonate and a fetus; and 1 symptomatic case in a child. Molecular analysis demonstrated that identical isolates of only 1 atypical strain were responsible for at least 5 of the 11 cases of toxoplasmosis in the outbreak. No epidemiological sources could be linked to this severe community-wide outbreak of toxoplasmosis.

CONCLUSION

This report is in agreement with the particular features of toxoplasmosis involving atypical strains that were recently described in French Guiana.

Microglia Produce IFN-γIndependently from T Cells During Acute Toxoplasmosis in the Brain

We previously reported a requirement of interferon-gamma (IFN-gamma) production by both T cells and cells other than T or natural killer (NK) cells in the brain for prevention of toxoplasmic encephalitis. In the present study, we examined whether microglia, the resident macrophage system in the brain, produce IFN-gamma in response to infection with Toxoplasma gondii in SCID and wild-type BALB/c mice. IFN-gamma was detected in the culture supernatants of microglia purified from the brains of SCID mice that had developed toxoplasmic encephalitis due to reactivation of infection. A significant increase in numbers of IFN-gamma-expressing microglia was also observed by immunostaining for this cytokine in the brains of SCID and BALB/c mice during the acute stage of acquired infection, and those numbers decreased in the later stage of infection in the BALB/c animals. These results indicate that microglia produce IFN-gamma in the presence and absence of T cells in response to reactivated or acute acquired infection in the brain. Because IFN-gamma is the essential effector molecule to control tachyzoites and because this cytokine is a potent inducer of expression of chemokines and MHC antigens important for recruitment and activation of T cells, IFN-gamma production by microglia might play a critical role in the early stage of tachyzoite proliferation in the brain by limiting parasite growth and initiating subsequent T cell immunity.

Prenatal screening and diagnosis of congenital toxoplasmosis: a review of safety issues and psychological consequences for women who undergo screening

As part of the EUROTOXO initiative, this review focuses on the potential risks associated with prenatal testing for congenital toxoplasmosis. We first review the evidence on the risks of adverse events associated with amniocentesis, which is required for definitive diagnosis of toxoplasmosis infection in the fetus, and for which the most important risk is fetal loss. To date, there has been only one randomized trial to document risks associated with amniocentesis. This trial, which was conducted in 1986, reported a procedure-related rate of fetal loss of 1.0% (95% CI, 0.3-1.5). However, evidence from available controlled studies suggests that the pregnancy loss associated with mid-trimester amniocentesis may be lower. Potential psychological consequences of prenatal testing for congenital toxoplasmosis include parental anxiety due to false positive results and uncertainties related to prognosis of children with a prenatal diagnosis of congenital toxoplasmosis. Parental anxiety may be particularly important in screening strategies that include more frequent screenings, which may in turn entail substantial, and at times unnecessary, anxiety or other negative consequences for women and their families. These negative psychological outcomes should be balanced against the benefits of testing, which can allow women to make an informed choice regarding the pregnancy.

Atomic resolution insight into host cell recognition by Toxoplasma gondii

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. Micronemal proteins (MICs) are released onto the parasite surface just before invasion of host cells and play important roles in host cell recognition, attachment and penetration. Here, we report the atomic structure for a key MIC, TgMIC1, and reveal a novel cell-binding motif called the microneme adhesive repeat (MAR). Using glycoarray analyses, we identified a novel interaction with sialylated oligosaccharides that resolves several prevailing misconceptions concerning TgMIC1. Structural studies of various complexes between TgMIC1 and sialylated oligosaccharides provide high-resolution insights into the recognition of sialylated oligosaccharides by a parasite surface protein. We observe that MAR domains exist in tandem repeats, which provide a highly specialized structure for glycan discrimination. Our work uncovers new features of parasite-receptor interactions at the early stages of host cell invasion, which will assist the design of new therapeutic strategies.

Toxoplasmosis

Infections with Toxoplasma gondii occur worldwide, but are especially prevalent in Europe, South America and Africa. The primary problem for the diagnosis of T. gondii infection is long-lasting IgM-antibodies, thus the presence of T. gondii-specific IgM-antibodies do not necessarily indicate an acute infection. The use of a Toxoplasma-specific IgG-avidity ratio, differentiated Western blots and two-dimensional immunoblots usually resolves diagnostic problems. There is no consensus on the best strategy to control congenital toxoplasmosis. Recent European prospective, but descriptive, studies including a meta-analysis of existing cohorts have found a surprisingly small effect on maternal-fetal transmission and clinical signs in children treated for T. gondii infection diagnosed by pre- and neonatal screening programmes. No randomised studies exist on the treatment of T. gondii infection in pregnant women and newborn children with congenital toxoplasmosis. Atovaquone is the most promising new drug available, but is not yet approved for use in pregnant women and small children.

Maternal–fetal transmission of Toxoplasma gondii in interferon-γ deficient pregnant mice

Toxoplasma gondii infection is generally asymptomatic in immunocompetent persons but can be life-threatening in immunocompromised persons and for fetuses in the case of maternal-fetal transmission. The effect of interferon (IFN)-gamma, which plays a crucial role in the protective immunity against T. gondii infection, on maternal-fetal transmission of T. gondii was analyzed by quantitative competitive polymerase chain reaction targeting T. gondii-specific SAG1 gene. T. gondii loads were obvious in uterus and placenta of wild type (WT) C57BL/6 (B6, susceptible strain) but not BALB/c (resistant strain) pregnant mice. Higher levels of T. gondii were detected in uterus and placenta of IFN-gamma knock-out (GKO) B6 and BALB/c than in those of WT mice. Furthermore, T. gondii was detected in fetus of GKO B6 but not GKO BALB/c, WT B6, or WT BALB/c mice. Thus, not only IFN-gamma but also genetic susceptibility to T. gondii infection was important for the protective immunity of maternal-fetal transmission of T. gondii to fetus via placenta. T. gondii-infected WT mice displayed a low delivery rate with high IFN-gamma production, whereas infected GKO mice did not. Additionally, mean body weight of neonates from T. gondii-infected GKO BALB/c pregnant mice was significantly lower than that of unaborted neonates from WT BALB/c pregnant mice, suggesting the effects of T. gondii infection on intrauterine growth retardation of fetus in pregnant GKO mice.

Prevention and treatment of congenital toxoplasmosis

Infection with Toxoplasma gondii is transmitted to man by infected meat or meat products and by contact with soil or surface water. In theory, prevention by hygienic measures is possible, but this has never been proved to work in practice. Therefore, pre- and postnatal screening has been implemented in several countries aiming at early diagnosis. However, data on the effect of treatment are limited and no randomized, controlled trials have been performed. The risk of T. gondii infection in Europe is declining and studies using historical controls from earlier decades cannot be used for decision making. The screening of pregnant women or neonates makes the assumption that any children diagnosed can be offered an effective treatment. There is an urgent need to test new drugs and demonstrate, using randomized, controlled trials, that the currently used drugs are effective.

Study on the prevalence of Toxoplasma gondii and Neospora caninum and molecular evidence of Encephalitozoon cuniculi and Encephalitozoon (Septata) intestinalis infections in red foxes (Vulpes vulpes) in rural Ireland

Thoracic fluid (pleural fluid and clotted blood) from 206 foxes were examined for antibodies to Toxoplasma gondii and 220 thoracic fluid samples were tested for Neospora caninum antibodies using indirect immunofluorescent antibody tests (IFAT). A total of 115 (56%) and six (3%) foxes had antibodies to T. gondii and N. caninum, respectively. The brains from 148 foxes were examined for histological lesions and pathological changes suggestive of parasitic encephalitis were observed in 33 (22%). Two thirds of these foxes had antibodies to T. gondii and one fox had antibodies to both T. gondii and N. caninum. PCR assays carried out on DNA extracted from the 33 brains with histological lesions were negative for N. caninum but one of the brains was positive for T. gondii. Microsporidian DNA was also amplified from the brains of two of these foxes. Sequencing these amplicons revealed 100% homology with Encephalitozoon (Septata) intestinalis in one fox and Encephalitozoon cuniculi in the second fox. This is the first report of Encephalitozoon infections in wildlife in Ireland.

Disease burden of congenital toxoplasmosis

Although the outcomes of toxoplasmosis have been well documented, an integrated estimate of the impact of this infection on the health status of the population is not available. "Disability-adjusted life years" are the sum of years of life lost and years lived with disability, weighted for the severity of the illness. The estimated disease burden of congenital toxoplasmosis in The Netherlands is 620 (range, 220-1900) disability-adjusted life years per year, which is similar to that for salmonellosis and is mainly caused by fetal loss and chorioretinitis. However, there is considerable uncertainty in this estimate. Scenario analysis indicates that the true burden may be underestimated. In other countries, the disease burden is expected to vary with the incidence of congenital infection, but it may also depend on the health care system. In countries that actively screen for toxoplasmosis, such as France, there may be a lower burden of morbidity but a higher burden of mortality.

A Family of Aspartic Proteases and a Novel, Dynamic and Cell-Cycle-Dependent Protease Localization in the Secretory Pathway of Toxoplasma gondii

Aspartic proteases are important virulence factors in pathogens like HIV, Candida albicans or Plasmodium falciparum. We report here the identification of seven putative aspartic proteases, TgASP1 to TgASP7, in the apicomplexan parasite Toxoplasma gondii. Bioinformatic and phylogenetic analysis of the TgASPs and other aspartic proteases from related Apicomplexa suggests the existence of five distinct groups of aspartic proteases with different evolutionary lineages. The members of each group share predicted biological features that validate the phylogeny. TgASP1 is expressed in tachyzoites, the rapidly dividing asexual stage of T.gondii. We present the proteolytic maturation and subcellular localization of this protease through the cell cycle. TgASP1 shows a novel punctate localization associated with the secretory system in non-dividing cells, and relocalizes dramatically and unambiguously to the nascent inner membrane complex of daughter cells at replication, before coalescing again at the end of division.

Importance of IFN-γ-Mediated Expression of Endothelial VCAM-1 on Recruitment of CD8+T Cells into the Brain During Chronic Infection withToxoplasma gondii

Interferon-gamma (IFNgamma) is essential for preventing reactivation of chronic infection with Toxoplasma gondii in the brain. We examined the role of IFNgamma on lymphocyte and endothelial adhesion molecule expression and T cell recruitment into the brain during chronic infection with T. gondii in IFNgamma knockout (IFNgamma(-/-)) and wild-type (WT) mice. Although the number of cerebral vessels expressing intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) increased in both WT and IFNgamma(-/-) mice following infection, there were more VCAM-1(+) vessels in brains of infected WT than of infected IFNgamma(-/-) mice; in contrast, numbers of ICAM-1(+) vessels did not differ between strains. We did not detect endothelial E-selectin, P-selectin, MAdCAM-1, or PNAd in any of the brains. Significantly fewer CD8(+) T cells were recruited into brains of infected IFNgamma(-/-) than WT mice. Treatment of infected IFNgamma(-/-) mice with recombinant IFN-gamma restored the expression of VCAM-1 on their cerebral vessels and recruitment of CD8(+) T cells into their brains, confirming an importance of this cytokine for upregulation of VCAM-1 expression and CD8(+) T cell trafficking. In infected WT and IFNgamma(-/-) animals, almost all cerebral CD8(+) T cells were lymphocyte function-associated antigen-1 (LFA-1)(high), CD44(high), and CD62L(neg), and approximately 38% were alpha4beta1 integrin(+). In adoptive transfer of immune spleen cells, pretreatment of the cells with a monoclonal antibody (mAb) against alpha4 integrin markedly inhibited recruitment of CD8(+) T cells into the brain of chronically infected WT mice. These results indicate that IFN-gamma-induced expression of endothelial VCAM-1 and its binding to alpha4beta1 integrin on CD8(+) T cells is important for recruitment of the T cells into the brain during the chronic stage of T. gondii infection, although LFA-1/ICAM-1 interaction may also be involved in this process.

Studies of Toxoplasma gondii and Plasmodium falciparum enoyl acyl carrier protein reductase and implications for the development of antiparasitic agents

Recent studies have demonstrated that submicromolar concentrations of the biocide triclosan arrest the growth of the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii and inhibit the activity of the apicomplexan enoyl acyl carrier protein reductase (ENR). The crystal structures of T. gondii and P. falciparum ENR in complex with NAD(+) and triclosan and of T. gondii ENR in an apo form have been solved to 2.6, 2.2 and 2.8 A, respectively. The structures of T. gondii ENR have revealed that, as in its bacterial and plant homologues, a loop region which flanks the active site becomes ordered upon inhibitor binding, resulting in the slow tight binding of triclosan. In addition, the T. gondii ENR-triclosan complex reveals the folding of a hydrophilic insert common to the apicomplexan family that flanks the substrate-binding domain and is disordered in all other reported apicomplexan ENR structures. Structural comparison of the apicomplexan ENR structures with their bacterial and plant counterparts has revealed that although the active sites of the parasite enzymes are broadly similar to those of their bacterial counterparts, there are a number of important differences within the drug-binding pocket that reduce the packing interactions formed with several inhibitors in the apicomplexan ENR enzymes. Together with other significant structural differences, this provides a possible explanation of the lower affinity of the parasite ENR enzyme family for aminopyridine-based inhibitors, suggesting that an effective antiparasitic agent may well be distinct from equivalent antimicrobials.

HIV infection with concomitant cerebral toxoplasmosis and disseminated histoplasmosis in a 45-year-old man

Although disseminated histoplasmosis is a common opportunistic infection in HIV patients in endemic areas, it is not widely known in Japan. We report a rare case of a man from Ghana infected with HIV who was hospitalized in Japan and who suffered from coinfection with cerebral toxoplasmosis and disseminated histoplasmosis. The diagnosis of cerebral toxoplasmosis was confirmed by a brain biopsy, and the therapy for the disease resulted in almost complete resolution of the brain lesion. However, fever of unknown origin continued for 2 weeks, and disseminated histoplasmosis was diagnosed by examination of a blood smear and by the detection of the histoplasma genome in the peripheral blood by means of polymerase chain reaction. The isolate was confirmed to be Histoplasma capsulatum var. duboisii. Therapy with amphotericin B was initiated, and no histoplasma genome in the peripheral blood was detected 3 days later. Unfortunately, the patient died after 10 days from acute respiratory syndrome. This case highlights that histoplasmosis should be included in the differential diagnosis of opportunistic infections in AIDS patients when patients have a history of travel to or arrival from endemic areas.

The toxofilin-actin-PP2C complex of Toxoplasma: identification of interacting domains

Toxofilin is a 27 kDa protein isolated from the human protozoan parasite Toxoplasma gondii, which causes toxoplasmosis. Toxofilin binds to G-actin, and in vitro studies have shown that it controls elongation of actin filaments by sequestering actin monomers. Toxofilin affinity for G-actin is controlled by the phosphorylation status of its Ser53, which depends on the activities of a casein kinase II and a type 2C serine/threonine phosphatase (PP2C). To get insights into the functional properties of toxofilin, we undertook a structure-function analysis of the protein using a combination of biochemical techniques. We identified a domain that was sufficient to sequester G-actin and that contains three peptide sequences selectively binding to G-actin. Two of these sequences are similar to sequences present in several G- and F-actin-binding proteins, while the third appears to be specific to toxofilin. Additionally, we identified two toxofilin domains that interact with PP2C, one of which contains the Ser53 substrate. In addition to characterizing the interacting domains of toxofilin with its partners, the present study also provides information on an in vivo-based approach to selectively and competitively disrupt the protein-protein interactions that are important to parasite motility.

Vaccination as a control strategy against the coccidial parasitesEimeria,ToxoplasmaandNeospora

The protozoan parasitesEimeriaspp.Toxoplasma gondiiandNeospora caninumare significant causes of disease in livestock worldwide andT. gondiiis also an important human pathogen. Drugs have been used with varying success to help control aspects of these diseases and commercial vaccines are available for all three groups of parasites. However, there are issues with increasing development of resistance to many of the anti-coccidial drugs used to help control avian eimeriosis and public concerns about the use of drugs in food animals. In addition there are no drugs available that can act against the tissue cyst stage of eitherT. gondiiorN. caninumand thus cure animals or people of infection. All three groups of parasites multiply within the cells of their host species and therefore cell mediated immune mechanisms are thought to be an important component of host protective immunity. Successful vaccination strategies for bothEimeriaandToxoplasmahave relied on using a live vaccination approach using attenuated parasites which allows correct processing and presentation of antigen to the host immune system to stimulate appropriate cell mediated immune responses. However, live vaccines can have problems with safety, short shelf-life and large-scale production; therefore there is continued interest in devising new vaccines using defined recombinant antigens. The major challenges in devising novel vaccines are to select relevant antigens and then present them to the immune system in an appropriate manner to enable the induction of protective immune responses. With all three groups of parasites, vaccine preparations comprising antigens from the different life cycle stages may also be advantageous. In the case ofEimeriaparasites there are also problems with strain-specific immunity therefore a cocktail of antigens from different parasite strains may be required. Improving our knowledge of the different parasite transmission routes, host-parasite relationships, disease pathogenesis and determining the various roles of the host immune response being at times host-protective, parasite protective and in causing immunopathology will help to tailor a vaccination strategy against a particular disease target. This paper discusses current vaccination strategies to help combat infections withEimeria,ToxoplasmaandNeosporaand recent research looking towards developing new vaccine targets and approaches.

Serological screening and toxoplasmosis exposure factors among pregnant women in the Democratic Republic of Sao Tome and Principe

The seroprevalence of Toxoplasma gondii infection among pregnant women in the Democratic Republic of Sao Tome and Principe (DRSTP) from November 2003 to March 2004 was determined by detection of serum anti-T. gondii antibodies. A short questionnaire interview for pregnant women was performed to investigate risk factors associated with T. gondii infection, including consumption of raw meat or unwashed vegetables, drinking unboiled water and keeping pets (cats and dogs). The overall seroprevalence of T. gondii infection was high (75.2%; 375/499). The older age group of > or =35 years had a significantly higher seroprevalence (85.7%; 54/63) than that of the younger age group of 15-25 years (70.4%; 178/253) (odds ratio 2.5, 95% CI 1.2-5.4; P=0.01). No significant difference in the seroprevalence of T. gondii infection was found between the pregnant women with and without exposure to the risk factors studied. However, among pregnant women with high antibody titers of > or =1:1024, it seemed likely that continual contact with pets and consumption of oocyst-contaminated water or raw unwashed vegetables rather than tissue cysts in meat was the primary route of infection. The incidence of congenital toxoplasmosis in unborn babies should be intensively monitored in the DRSTP.

Recurrent headache as the main symptom of acquired cerebral toxoplasmosis in nonhuman immunodeficiency virus-infected subjects with no lymphadenopathy: the parasite may be responsible for the neurogenic inflammation postulated as a cause of different types of headaches

Headache and/or migraine, a common problem in pediatrics and internal medicine, affect about 5% to 10% children and adolescents, and nearly 30% of middle-aged women. Headache is also one of the most common clinical manifestations of acquired Toxoplasma gondii infection of the central nervous system (CNS) in immunosuppressed subjects. We present 11 apparently nonhuman immunodeficiency virus-infected children aged 7 to 17 years (8 girls, 3 boys) and 1 adult woman with recurrent severe headaches in whom latent chronic CNS T. gondii infection not manifested by enlarged peripheral lymph nodes typical for toxoplasmosis, was found. In 7 patients, the mean serum IgG Toxoplasma antibodies concentration was 189 +/- 85 (SD) IU/mL (range 89 to 300 IU/mL), and in 5 other subjects, the indirect fluorescent antibody test titer ranged from 1:40 to 1:5120 IU/mL (n= <1:10 IU/mL). Some of the patients suffered also from atopic dermatitis (AD) and were exposed to cat and/or other pet allergens, associated with an increased IL-4 and decreased IFN-gamma production. These cytokine irregularities caused limited control of cerebral toxoplasmosis probably because IL-4 down-regulated both the production of IFN-gamma and its activity, and stimulated production of a low NO-producing population of monocytes, which allowed cysts rupture, increased parasite multiplication and finally reactivation of T. gondii infection. The immune studies performed in 4 subjects showed a decreased percentage of T lymphocytes, increased total number of lymphocytes B and serum IgM concentration, and impaired phagocytosis. In addition, few of them had also urinary tract diseases known to produce IL-6 that can mediate immunosuppressive functions, involving induction of the anti-inflammatory cytokine IL-10. These disturbances probably resulted from the host protective immune reactions associated with the chronic latent CNS T. gondii infection/inflammation. This is consistent with significantly lower enzyme indoleamine 2,3-dioxygenase (IDO) activity reported in atopic than in nonatopic individuals, and an important role that IDO and tryptophan degradation pathways plays in both, the host resistance to T. gondii infection and its reactivation. Analysis of literature information on the subjects with different types of headaches caused by foods, medications, and other substances, may suggest that their clinical symptoms and changes in laboratory data result at least in part from interference of these factors with dietary tryptophan biotransformation pathways. Several of these agents caused headache attacks through enhancing NO production via the conversion of arginine to citrulline and NO by the inducible nitric oxide synthase enzyme, which results in the high-output pathway of NO synthesis. This increased production of NO is, however, quickly down-regulated by NO itself because this biomolecule can directly inactivate NOS, may inhibit Ia expression on IFN-gamma-activated macrophages, which would limit antigen-presenting capability, and block T-cell proliferation, thus decreasing the antitoxoplasmatic activity. Moreover, NO inhibits IDO activity, thereby suppressing kynurenine formation, and at least one member of the kynurenine pathway, 3-hydroxyanthranilic acid, has been shown to inhibit NOS enzyme activity, the expression of NOS mRNA, and activation of the inflammatory transcription factor, nuclear factor-kB. In addition, the anti-inflammatory cytokines IL-4 and IL-10, TGF-beta, and a cytokine known as macrophage deactivating factor, have been shown to directly modulate NO production, sometimes expressing synergistic activity. On the other hand, IL-4 and TGF-beta can suppress IDO activity in some cells, for example human monocytes and fibroblasts, which is consistent with metabolic pathways controlled by IDO being a significant contributor to the proinflammatory system. Also, it seems that idiopathic intracranial hypertension, pseudotumor cerebri, and aseptic meningitis, induced by various factors, may result from their interference with IDO and inducible nitric oxide synthase activities, endogenous NO level, and cytokine irregularities which finally affect former T. gondii status 2mo in the brain. All these biochemical disturbances caused by the CNS T. gondii infection/inflammation may also be responsible for the relationship found between neurologic symptoms, such as headache, vertigo, and syncope observed in apparently immunocompetent children and adolescents, and physical and psychiatric symptoms in adulthood. We therefore believe that tests for T. gondii should be performed obligatorily in apparently immunocompetent patients with different types of headaches, even if they have no enlarged peripheral lymph nodes. This may help to avoid overlooking this treatable cause of the CNS disease, markedly reduce costs of hospitalization, diagnosis and treatment, and eventually prevent developing serious neurologic and psychiatric disorders.

Prevalence of antibodies against Toxoplasma gondii and Neospora caninum in Hungarian red foxes (Vulpes vulpes)

In the present study we have investigated the seroprevalence to the protozoan parasites Toxoplasma gondii and Neospora caninum in 337 red foxes (Vulpes vulpes) from 16 out of 19 counties in Hungary. The foxes were originally collected within a National vaccination program against rabies. Antibodies to T. gondii were detected in as many as 228 (68%) of the foxes using a commercial direct agglutination test (DAT). In an indirect iscom ELISA, five foxes (1.5%) were positive for antibodies against N. caninum. The high prevalence of foxes positive for T. gondii might be explained by the widespread occurrence of the parasite in the diet of foxes. As a contrast, latent infections of N. caninum among red foxes in Hungary are much less common.

Acidification of the parasitophorous vacuole containing Toxoplasma gondii in the presence of hydroxyurea

Toxoplasma gondii multiplies within parasitophorous vacuole that is not recognized by the primary no oxidative defense of host cells, mainly represented by the fusion with acidic organelles. Recent studies have already shown that hydroxyurea arrested the intracellular parasites leading to its destruction. In the present work we investigated the cellular mechanism involved in the destruction of intracellular Toxoplasma gondii. Fluorescent vital stains were used in order to observe possible acidification of parasitophorous vacuole-containing Toxoplasma gondii in presence of hydroxyurea. Vero cells infected with tachyzoites were treated with hydroxyurea for 12, 24 or 48 hours. Fluorescence, indicative of acidification, was observed in the parasitophorous vacuole when the cultures were incubated in presence of acridine orange. LysoTracker red was used in order to determine whether lysosomes were involved in the acidification process. An intense fluorescence was observed after 12 and 24 hours of incubation with hydroxyurea, achieving it is highly intensity after 48 hours of treatment. Ultrastructural cytochemistry for localization of the acid phosphatase lysosomal enzyme was realized. Treated infected cultures showed reaction product in vesicles fusing with vacuole or associated with intravacuolar parasites. These results suggest that fusion with lysosomes and acidification of parasitophorous vacuole leads to parasites destruction in the presence pf hydroxyurea.

Toxoplasma gondii inhibits toll-like receptor 4 ligand-induced mobilization of intracellular tumor necrosis factor alpha to the surface of mouse peritoneal neutrophils

Neutrophils are well-known to rapidly respond to infection through chemotactic infiltration at sites of inflammation, followed by rapid release of microbicidal molecules, chemokines, and proinflammatory cytokines. For tumor necrosis factor alpha (TNF-alpha), we recently found that neutrophils contain intracellular pools of the cytokine and display the capacity to upregulate transcriptional activity of the gene during lipopolysaccharide (LPS) stimulation. We now show that triggering of mouse peritoneal neutrophils with Toll-like receptor 2 (TLR2), TLR4, and TLR9 ligands, but not ligands of TLR3, induces upregulation of surface membrane TNF-alpha. However, neutrophils infected with the protozoan Toxoplasma gondii displayed an inability to respond fully in terms of TLR ligand-induced increases in membrane TNF-alpha expression. Infected neutrophils failed to display decreased levels of intracellular TNF-alpha upon LPS exposure. In contrast to intermediate inhibitory effects in nontreated neutrophils, T. gondii induced a complete blockade in LPS-induced surface TNF-alpha expression in the presence of the protein synthesis inhibitor cycloheximide. Despite these inhibitory effects, the parasite did not affect LPS-induced upregulation of TNF-alpha gene transcription. Collectively, the results show that Toxoplasma prevents TLR ligand-triggered mobilization of TNF-alpha to the neutrophil surface, revealing a novel immunosuppressive activity of the parasite.

Toxoplasma gondii purine nucleoside phosphorylase biochemical characterization, inhibitor profiles, and comparison with the Plasmodium falciparum ortholog

Purine nucleoside phosphorylase (PNP) is an important component of the nucleotide salvage pathway in apicomplexan parasites and a potential target for drug development. The intracellular pathogen Toxoplasma gondii was therefore tested for sensitivity to immucillins, transition state analogs that exhibit high potency against PNP in the malaria parasite Plasmodium falciparum. Growth of wild-type T. gondii is unaffected by up to 10 microm immucillin-H (ImmH), but mutants lacking the (redundant) purine salvage pathway enzyme adenosine kinase are susceptible to the drug, with an IC50 of 23 nm. This effect is rescued by the reaction product hypoxanthine, but not the substrate inosine, indicating that ImmH acts via inhibition of T. gondii PNP. The primary amino acid sequence of TgPNP is >40% identical to PfPNP, and recombinant enzymes exhibit similar kinetic parameters for most substrates. Unlike the Plasmodium enzyme, however, TgPNP cannot utilize 5'-methylthio-inosine (MTI). Moreover, TgPNP is insensitive to methylthio-immucillin-H (MT-ImmH), which inhibits PfPNP with a Ki* of 2.7 nm. MTI arises through the deamination of methylthio-adenosine, a product of the polyamine biosynthetic pathway, and its further metabolism to hypoxanthine involves PfPNP in purine recycling (in addition to salvage). Remarkably, analysis of the recently completed T. gondii genome indicates that polyamine biosynthetic machinery is completely lacking in this species, obviating the need for TgPNP to metabolize MTI. Differences in purine and polyamine metabolic pathways among members of the phylum Apicomplexa and these parasites and their human hosts are likely to influence drug target selection strategies. Targeting T. gondii PNP alone is unlikely to be efficacious for treatment of toxoplasmosis.

Zoonotic implications of the swine-transmitted protozoal infections

Pig production is an important part of the economy in many countries. Domestic and wild pigs (Sus scrofa) are susceptible to a wide range of infectious and parasitic diseases. Some of these diseases are specifically limited to pigs while some of the other diseases are shared with other species of wildlife and domestic livestock. As the numbers and geographic distribution of wild and domestic swines continue to increase, it is certain that the number of contacts between these swines and domestic livestock will also increase, as will the probability of human exposure to the parasites of swine directly or indirectly. Here, we will discuss the protozoal infections of pigs, which have the potential to infect humans and provide reasonable risk assessment for zoonotic transmission.

Expression, purification and preliminary crystallographic analysis of the Toxoplasma gondii enoyl reductase

Crystals of T. gondii ENR in complex with NAD⁺ and triclosan were grown using the hanging-drop vapour-diffusion method with PEG 8000 as precipitant.

The protozoan parasite Toxoplasma gondii is the causative agent of one of the most widespread parasitic infections of man and is a leading cause of congenital neurological birth defects and the third most common cause of food-borne deaths in the United States. Despite this, to date no drugs are available that provide a fully effective treatment. Recently, the antibacterial agent triclosan was shown to inhibit the fatty-acid biosynthesis pathway in T. gondii and to interact with the enoyl reductase (ENR). In order to analyse the potential of triclosan as a lead compound targeting T. gondii ENR and to explore unique features of the apicomplexan enzyme that could be exploited in future drug development, structural studies have been initiated on T. gondii ENR. Crystals of T. gondii ENR in complex with NAD⁺ and triclosan were grown using the hanging-drop vapour-diffusion method with PEG 8000 as precipitant. The crystals belong to space group P3₂21, with approximate unit-cell parameters a = 78.1, b = 78.1, c = 188.5 Å, α = β = 90, γ = 120° and a dimer in the asymmetric unit. Test data were collected to beyond 2.6 Å on cryocooled crystals (100 K) using a Rigaku MM007 rotating-anode X-ray source, revealing that the crystals are suitable for a full structural determination.

New Vidas assay for Toxoplasma-specific IgG avidity: evaluation on 603 sera

After the development of the new version of the test Vidas Toxo IgG with antigens obtained from tachyzoites cultured on cells, a Vidas avidity test has been recently developed. The aim of this study was to assess the value of the determination of avidity on the new Vidas test. This avidity test was performed on 553 sera obtained from pregnant women whose dates of infection had been determined and on 50 sera obtained from immunosuppressed patients. In the group of infection occurring less than 4 months before sampling, the avidity index was <0.3 on 266 among 267 sera. In the group of infection occurring more than 15 months before sampling, the avidity index was >0.3 for 44/46 sera of pregnant women and for 47/47 sera of immunosuppressed patients. Thus, the new version of avidity test was helpful primarily to rule out that an infection had occurred within the prior 4 months.

Toxoplasma gondiitriggers Gi-dependent PI 3-kinase signaling required for inhibition of host cell apoptosis

Infection with the intracellular parasite Toxoplasma gondii renders cells resistant to multiple pro-apoptotic signals, but underlying mechanisms have not been delineated. The phosphoinositide 3-kinase (PI 3-kinase) pathway and the immediate downstream effector protein kinase B (PKB/Akt) play important roles in cell survival and apoptosis inhibition. Here, we show that Toxoplasma infection of mouse macrophages activates PKB/Akt in vivo and in vitro. In a mixed population of infected and non-infected macrophages, activation is only observed in parasite-infected cells. The PI 3-kinase inhibitors wortmannin and LY294002 block parasite-induced PKB phosphorylation. PKB activation occurs independently of Toll-like receptor adaptor protein MyD88 but uncoupling of Gi-protein-mediated signaling with pertussis toxin prevents PKB phosphorylation. Moreover, in the presence of PI 3-kinase inhibitors or pertussis toxin, not only PKB activation but also ERK1/2 activation during T. gondii infection is defective. Most importantly, the parasite's ability to induce macrophage resistance to pro-apoptotic signaling is prevented by incubation with PI 3-kinase inhibitors. This study demonstrates that T. gondii exploits host Gi-protein-dependent PI 3-kinase signaling to prevent induction of apoptosis in infected macrophages.

A requirement for the Vgamma1+ subset of peripheral gammadelta T cells in the control of the systemic growth of Toxoplasma gondii and infection-induced pathology

gammadelta T cells are a diverse population of T cells that are widely distributed and are a common feature of pathogen-induced immune responses. It is not clear, however, whether different populations of gammadelta T cells have specific functions, and what factors determine the functional properties of individual populations. A murine model of peroral Toxoplasma gondii infection was used to determine the contribution Vgamma1+ intestinal intraepithelial lymphocytes (IELs) vs systemic Vgamma1+ T cells make to the acute and chronic stages of the host immune response, and whether the macrophage cytocidal activity of Vgamma1+ T cells described in bacterial infections is seen in other, unrelated infectious disease models. In response to oral infection with virulent type 1 or avirulent type II strains of T. gondii, TCR-delta-/- mice rapidly developed severe ileitis. In contrast, in mice deficient in Vgamma1+ T cells and IELs and wild-type mice, inflammation was delayed in onset and less severe. The protective effect of (Vgamma1-) IELs to Toxoplasma infection was unrelated to their cytolytic and cytokine (Th1)-producing capabilities. Systemic Vgamma1+ T cells were shown to play an essential role in limiting parasite growth and inflammation in peripheral tissues and, in particular, in the CNS, that was associated with their ability to efficiently kill parasite-elicited and infected macrophages. These findings suggest that macrophage cytocidal activity of Vgamma1+ T cells may be a universal feature of pathogen-induced immune responses and that microenvironmental factors influence the involvement and function of gammadelta T cells in the host response to infection.

Prevalence of Toxoplasma gondii antibodies in red deer (Cervus elaphus) and other wild ruminants from Spain

Serum samples from 441 red deer (Cervus elaphus) and 161 other wild ruminant species, collected between 1993 and 2005 from six regions of Spain were tested for antibodies against Toxoplasma gondii by the modified agglutination test (MAT). Antibodies to T. gondii (MAT 1:25 or higher) were detected in 15.6% of red deer. Statistically significant differences were observed among sampling sites with seroprevalence in red deer from Catalonia (42.2%) being significantly higher compared with other Spanish regions (8.7%) (P < 0.05). Statistically significant differences were not observed between T. gondii seroprevalence and sex, age or management of hunting estates (open versus fenced). Seroprevalence of T.gondii infection in other ruminants species was 24% of 79 fallow deer (Dama dama), 21.8% of 33 in roe deer (Capreolus capreolus), 33.3% of three Spanish ibex (Capra pyrenaica), 20% of 10 chamois (Rupicapra pyrenaica), 10% of 10 barbary sheep (Ammotragus lervia), and 14.8% of 27 mouflon (Ovis ammon) in areas not including Catalonia, where no samples from these species were available. Serological results indicated a widespread exposure to T. gondii among wildlife in Spain and suggest that consumption of raw or inadequately cooked meat, as well as handling carcasses of wild game, should be taken into account as a source of infection for humans.

Antemortem diagnosis and treatment of toxoplasmosis in two cats on cyclosporin therapy

Clinical toxoplasmosis was diagnosed antemortem in two cats being treated with therapeutic doses of cyclosporin. The diagnosis was made by detecting tachyzoites on cytological examination of bronchoalveolar lavage fluid from one case and pleural effusion from the other. Despite early diagnosis and aggressive treatment in both cases, only one cat survived. Reactivation of latent Toxoplasma gondii infection secondary to cyclosporin-induced immunosuppression was considered likely in both cases. The presence of respiratory signs in cats treated with cyclosporin should alert clinicians to the possibility of clinical toxoplasmosis. Consideration should be given to determining the serostatus of cats to T gondii prior to use of drugs which are potent inhibitors of cell mediated immunity, such as cyclosporin. Two cases of feline toxoplasmosis are presented.

Toxoplasma gondii is capable of exogenous folate transport. A likely expansion of the BT1 family of transmembrane proteins

Folates are key elements in eukaryotic biosynthetic processes. The protozoan parasite Toxoplasma gondii possesses the enzymes necessary for de novo folate synthesis and has been suggested to lack alternative mechanisms for folate acquisition. In this paper, we present a different view by providing evidence that Toxoplasma is capable of salvaging exogenous folates. By monitoring uptake of radiolabeled folates by parasites in axenic conditions, our studies revealed a common folate transporter that has a high affinity for folic acid. Transport of this compound across the parasite plasma membrane is rapid, biphasic, temperature dependent, bi-directional, concentration dependent and specific. In addition, morphological evidence demonstrates that fluorescent methotrexate, a folate analog, is internalized by Toxoplasma and shows localization reminiscent to the mitochondrion. The presence of putative folate transporter genes in the Toxoplasma genome, which are homologous to the BT1 family of proteins, suggests that Toxoplasma may encode proteins involved in folate transport. Interestingly, genome analysis suggests that the BT1 family of proteins exists not only in Toxoplasma, but in other Apicomplexan parasites as well. Altogether, our results not only have implications for current therapeutic regimens against T. gondii, but they also allude that the folate transport mechanism may represent a novel Apicomplexan target for the development of new drugs.

Diagnosis of cerebral toxoplasmosis in AIDS patients in Brazil: importance of molecular and immunological methods using peripheral blood samples

Cerebral toxoplasmosis is the most common cerebral focal lesion in AIDS and still accounts for high morbidity and mortality in Brazil. Its occurrence is more frequent in patients with low CD4(+) T-cell counts. It is directly related to the prevalence of anti-Toxoplasma gondii antibodies in the population. Therefore, it is important to evaluate sensitive, less invasive, and rapid diagnostic tests. We evaluated the value of PCR using peripheral blood samples on the diagnosis of cerebral toxoplasmosis and whether its association with immunological assays can contribute to a timely diagnosis. We prospectively analyzed blood samples from 192 AIDS patients divided into two groups. The first group was composed of samples from 64 patients with cerebral toxoplasmosis diagnosed by clinical and radiological features. The second group was composed of samples from 128 patients with other opportunistic diseases. Blood collection from patients with cerebral toxoplasmosis was done before or on the third day of anti-toxoplasma therapy. PCR for T. gondii, indirect immunofluorescence, enzyme-linked immunosorbent assay, and an avidity test for toxoplasmosis were performed on all samples. The PCR sensitivity and specificity for diagnosis of cerebral toxoplasmosis in blood were 80% and 98%, respectively. Patients with cerebral toxoplasmosis (89%) presented higher titers of anti-T. gondii IgG antibodies than patients with other diseases (57%) (P<0.001). These findings suggest the clinical value of the use of both PCR and high titers of anti-T. gondii IgG antibodies for the diagnosis of cerebral toxoplasmosis. This strategy may prevent more invasive approaches.

Purine and pyrimidine transport in pathogenic protozoa: From biology to therapy

Purine salvage is an essential function for all obligate parasitic protozoa studied to date and most are also capable of efficient uptake of preformed pyrimidines. Much progress has been made in the identification and characterisation of protozoan purine and pyrimidine transporters. While the genes encoding protozoan or metazoan pyrimidine transporters have yet to be identified, numerous purine transporters have now been cloned. All protozoan purine transporter-encoding genes characterised to date have been of the Equilibrative Nucleoside Transporter family conserved in a great variety of eukaryote organisms. However, these protozoan transporters have been shown to be sufficiently different from mammalian transporters to mediate selective uptake of therapeutic agents. Recent studies are increasingly addressing the structure and substrate recognition mechanisms of these vital transport proteins.

A decade of discoveries in veterinary protozoology changes our concept of “subclinical” toxoplasmosis

One of the most compelling topics to emerge from the last decade of veterinary protozoology is disease caused by a zoonotic pathogen, Toxoplasma gondii, in otherwise healthy people. These findings may catch the health professions by surprise, because veterinary and medical courses and textbooks typically emphasize that T. gondii infections are subclinical, unless acquired in utero or the patient has a serious immunosuppressive condition. Nevertheless, numerous reports in the last decade associate toxoplasmosis with lymphadenopathy, fever, weakness and debilitation, ophthalmitis, and severe multisystemic infections in people who do not have immunosuppressive conditions. Toxoplasmosis in rodents causes altered behavior, and similar mental aberrations are coming to light in humans; recent studies associate T. gondii infection with personality shifts and increased likelihood of reduced intelligence or schizophrenia. These conditions reduce the quality of life of individuals, and may exact a significant economic burden upon society. Of course, toxoplasmosis continues to cause serious conditions in AIDS patients and congenitally infected people, as well as abortions and encephalitis in domestic and wild animals. Environmental contamination is heavy enough to extend into marine wildlife. It is time for the health professions to amend teaching curricula regarding T. gondii. Veterinary parasitologists should lead the way in developing methods to reduce the prevalence of T. gondii in food animals. Public health policies should prohibit the practice of allowing pet cats to roam. Organizations and individuals that feed feral cats are unwittingly contributing to the dissemination of T. gondii, by sustaining artificially dense populations of a definitive host of this protozoal parasite.

Seroprevalence of Toxoplasma gondii in northern Greece during the last 20 years

The seroprevalence of Toxoplasma gondii in the northern Greek population was determined in 1984, 1994 and 2004, and changes during this period were investigated. In total, 1014, 812 and 958 sera from individuals aged 1 day to 70 years were examined in 1984, 1994 and 2004, respectively, for IgG and IgM anti-Toxoplasma antibodies with the standard immunofluorescence assay (IFA) and microparticle enzyme immunoassay (MEIA). In individuals positive for IgM-specific antibodies, primary infection with Toxoplasma was diagnosed on the basis of the Toxoplasma serological profile (IFA, MEIA, conventional IgM and IgA ELISAs, immunosorbent agglutination assay and IgG avidity test). The prevalence of IgG-specific antibodies in the general population was 37%, 29.9% and 24.1% in 1984, 1994 and 2004, respectively, and was 35.6%, 25.6% and 20%, respectively, in women of reproductive age (15-39 years). The incidence of Toxoplasma infection, based on cases of primary infection and the annual seroconversion rate for the general population, was estimated to be 1.25% and 1.1% in 1984, 1.05% and 0.93% in 1994, and 0.85% and 0.8% in 2004. The significant decline in prevalence, and the shift towards an older age group, observed during this period could be explained by the improved socio-economic situation. The high (80%) proportion of women of reproductive age susceptible to Toxoplasma infection, with an estimated 90-200 neonates infected in utero annually, seems to present a potential risk to public health. Education of the public and prophylactic measures may become increasingly important.

Parasitic central nervous system infections in immunocompromised hosts

Immunosuppression due to therapy after transplantation or associated with HIV infection increases susceptibility to various central nervous system (CNS) infections. This article discusses how immunosuppression modifies the presentation, diagnosis, and treatment of selected parasitic CNS infections, with a focus on toxoplasmosis, Chagas disease, neurocysticercosis, schistosomiasis, and strongyloidiasis.

A GFP-based motif-trap reveals a novel mechanism of targeting for the Toxoplasma ROP4 protein

The protozoan parasite Toxoplasma gondii is a highly specialized eukaryote that contains a remarkable number of intracellular compartments, some unique to Apicomplexans and others typical of eukaryotes in general. We have established a green fluorescent protein (GFP)-based motif-trap to identify proteins targeted to different intracellular locations and subsequently the signals responsible for this sorting. The motif-trap involves the transfection and integration of a linearized GFP construct which lacks a promoter and an initiator methionine codon. FACS is used to isolate parasites in which GFP fuses in-frame into a coding region followed by screening by fluorescence microscopy for those containing GFP targeted to specific intracellular compartments. GFP trapping was successful using vectors designed for integration into regions encoding exons and vectors that were engineered with a splice acceptor site for integration into regions encoding introns. This strategy differs from most protein traps in that the resulting fusions are expressed from the endogenous promoter and starting methionine. Thus, problems from inappropriate expression levels or the creation of fortuitous targeting signals seen in library-based traps are diminished. Using this approach, we have trapped GFP localized to a number of intracellular compartments including the nucleus, nucleolus, endoplasmic reticulum, cytosol, parasite surface and rhoptries of Toxoplasma. Further analysis of a parasite clone containing GFP targeted to the rhoptries shows GFP fused to the gene encoding the rhoptry protein ROP4 and has elucidated an additional mechanism for targeting of this protein.

Manipulation of mitogen-activated protein kinase/nuclear factor-kappaB-signaling cascades during intracellular Toxoplasma gondii infection

The intracellular protozoan Toxoplasma gondii exerts profound effects on nuclear factor-kappaB (NF-kappaB)- and mitogen-activated protein kinase (MAPK)-signaling cascades in macrophages. During early infection, nuclear translocation of NF-kappaB is blocked, and later, the cells display defects in lipopolysaccharide (LPS)-induced MAPK phosphorylation after undergoing initial activation in response to Toxoplasma itself. Infected macrophages that are subjected to triggering through Toll-like receptor 4 (TLR4) with LPS display defective production of tumor necrosis factor-alpha and IL-12 (IL-12) that likely reflects interference with NF-kappaB- and MAPK-signaling cascades. Nevertheless, T. gondii possesses molecules that themselves induce eventual proinflammatory cytokine synthesis. For interleukin-12, this occurs through both myeloid differentiation factor 88-dependent and chemokine receptor CCR5-dependent pathways. The balance between activation and interference with proinflammatory signaling is likely to reflect the need to achieve an appropriate level of immunity that allows the host and parasite to maintain a stable interaction.

DNA extraction and PCR assays for detection of Toxoplasma gondii

For detection of Toxoplasma gondii we compared the sensitivity of two different DNA extraction methods and three different PCR assays. Sensitivities of DNA extraction by QIAamp DNA mini Kit or MagNa pure followed by PCR, nested PCR and oligochromatography or Light Cycler PCR using either SYBR green chemistry or TaqMan probe were compared. No significant difference between extraction methods was found using pure T. gondii tachyzoites. Spiked blood samples, 10(4) to 10 parasites per sample, generated no difference in sensitivity between the two DNA extraction methods when analysed by nested PCR detected by oligochromatography or analysed by Light Cycler PCR TaqMan. In spiked blood samples Light Cycler PCR SYBR green was unable to detect the parasite and a reduction in sensitivity was observed with the TaqMan assay. Conventional PCR was more sensitive when DNA was extracted from the spiked samples using the QIAamp DNA mini Kit. Conventional and nested PCR were found to be more sensitive than Light Cycler PCR TaqMan using the QIAamp DNA mini Kit. It was not possible to use Light Cycler PCR SYBR green in blood samples. Conventional PCR was more sensitive for detection of T. gondii in spiked blood samples using QIAamp DNA mini Kit DNA extraction, suggesting that the choice of DNA extraction method may affect PCR assays differently.

Migration and maturation of human dendritic cells infected with Toxoplasma gondii depend on parasite strain type

Migration and maturation of human dendritic cells derived from CD34+ progenitor cells (DC) infected by Toxoplasma gondii were studied in an in vitro model. We demonstrated that infection with virulent type I strains RH and ENT or type II low virulent strains PRU and CAL induced DC migration towards MIP-3beta. However, type II strains induced a higher percentage of migrating cells than that induced by type I strains or positive controls (chemical allergen or lipopolysaccharides). Type II strains produced soluble factors responsible of the high migration whereas heat killed tachyzoites did not induced a migration higher than positive controls. We also demonstrated that infection by virulent strains and not by type II stains or heat killed tachyzoites triggers DC maturation. A soluble factor released by type II strains was responsible of the absence of DC maturation. Taken together, these results demonstrated that the interference of T. gondii in the behaviour of DC functions is related to the strain types and can be supported by secretion of soluble factors by the parasite.

PCR assay using cerebrospinal fluid for diagnosis of cerebral toxoplasmosis in Brazilian AIDS patients

Highly active antiretroviral therapy has decreased the incidence of opportunistic infections in the central nervous system in AIDS patients. However, neurological abnormalities still remain important causes of mortality and morbidity in developing countries. In Brazil, cerebral toxoplasmosis is the most common cerebral mass lesion in AIDS patients. For these reasons, early, inexpensive, and sensitive diagnostic tests must be evaluated. The aim of this study was to evaluate PCR, using cerebrospinal fluid (CSF) samples to detect Toxoplasma gondii DNA, and to determine if the association of PCR with immunological assays can contribute to a timely diagnosis. We studied two sample groups. First, we analyzed stored CSF samples from 29 newborns and from 39 adults with AIDS without a definitive diagnosis of toxoplasmosis. The goal of this step was to standardize the methodology with a simple and economical procedure to recover the T. gondii DNA. Next, we prospectively evaluated CSF samples from 12 AIDS patients with a first episode of cerebral toxoplasmosis and 18 AIDS patients with other neurological opportunistic diseases and without previous cerebral toxoplasmosis. In all PCR samples, an indirect immunofluorescent assay and an enzyme-linked immunosorbent assay were performed. Samples from all patients with cerebral toxoplasmosis presented positive PCR results (sensitivity, 100%), and a sample from one of the 18 AIDS patients with other neurological diseases also presented positive PCR results (specificity, 94.4%). These findings suggest the clinical utility of PCR in the diagnosis of cerebral toxoplasmosis in developing countries.

Functional inactivation of immature dendritic cells by the intracellular parasite Toxoplasma gondii

Despite its noted ability to induce strong cellular immunity, and its known susceptibility to IFN-gamma-dependent immune effector mechanisms, the protozoan Toxoplasma gondii is a highly successful parasite, able to replicate, disseminate, and either kill the host or, more commonly, establish resistant encysted life forms before the emergence of protective immune responses. We sought to understand how the parasite gains the advantage. Using transgenic clonal parasite lines engineered to express fluorescent markers in combination with dendritic cells (DC) grown from the bone marrow of wild-type mice or transgenic mice expressing fluorescent protein-tagged MHC class II molecules, we used flow cytometry and fluorescence microscopy to analyze the responses of infected DC to both invasion by the parasite and subsequent DC maturation signals. We found that T. gondii preferentially invades immature dendritic cells but fails to activate them in the process, and renders them resistant to subsequent activation by TLR ligands or the immune-system-intrinsic maturation signal CD40L. The functional consequences of T. gondii-mediated suppression of DC activation are manifested in a relative inability of infected immature DC to activate naive CD4(+) Th lymphocytes, or to secrete cytokines, such IL-12 and TNF-alpha, that play important roles in innate and/or adaptive immunity. The findings reveal that T. gondii suppresses the ability of immature DC to participate in innate immunity and to induce adaptive immune responses. The ability of T. gondii to temporarily evade recognition could provide a selective advantage that permits dissemination and establishment before adaptive immune response initiation.

Does toxoplasmosis cause DNA damage? An evaluation in isogenic mice under normal diet or dietary restriction

Toxoplasmosis is an anthropozoonotic widespread disease, caused by the coccidian protozoan parasite Toxoplasma gondii. Since there are no data regarding the genotoxicity of the parasite in vivo, this study was designed to evaluate the genotoxic potential of the toxoplasmosis on isogenic mice with normal diet or under dietary restriction and submitted to a treatment with sulfonamide (375 microg/kg per day). DNA damage was assessed in peripheral blood, liver and brain cells using the comet assay (tail moment). The results for leucocytes showed increases in the mean tail moment in mice under dietary restriction; in infected mice under normal diet; in infected, sulfonamide-treated mice under normal diet; in infected mice under dietary restriction and in infected sulfonamide-treated mice under dietary restriction. In liver and brain cells, no statistically significant difference was observed for the tail moment. These results indicated that dietary restriction and T. gondii were able to induce DNA damage in peripheral blood cells, as detected by the comet assay.

Toxoplasma gondii interferes with lipopolysaccharide-induced mitogen-activated protein kinase activation by mechanisms distinct from endotoxin tolerance

We show in this study that Toxoplasma gondii infection induces rapid activation of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase 1/2, and stress-activated protein kinase/c-Jun N-terminal kinase MAPK, followed promptly by their deactivation in mouse macrophages. Nevertheless, when infected cells were subsequently subjected to LPS triggering, MAPK activation was severely defective, in particular in the case of p38 MAPK, which is required for LPS-triggered TNF-alpha and IL-12 production. Similar effects occurred during endotoxin tolerance, but the phenomena were distinct. LPS pretriggering failed to activate the major p38 MAPK kinase, MAPK kinase 3/6. Toxoplasma infection, in contrast, resulted in sustained activation of this kinase. Furthermore, endotoxin pre-exposure blocked IkappaBalpha degradation upon subsequent LPS triggering, but this was not the case for Toxoplasma preinfection. Endotoxin-mediated down-regulation of the LPS receptor, Toll-like receptor 4, has been suggested as one possible mechanism contributing to tolerance, and we found in this study that LPS down-modulated Toll-like receptor 4 expression. In contrast, Toxoplasma infection induced up-regulation of this pattern recognition receptor. Our results show that T. gondii blocks LPS-triggered cytokine production in part through MAPK inactivation, and that this occurs through pathways distinct from endotoxin-induced tolerance.

The International Congress on Toxoplasmosis

Toxoplasma gondii is an important pathogen in both veterinary and human medicine. Infection during pregnancy can result in fetal transmission and a congenital infection syndrome. In immune-compromised hosts reactivation of latent infection can result in encephalitis. It has been estimated that as many as one-third of the human population harbours this zoonosis. The Seventh International Congress on Toxoplasmosis, organised by Louis M. Weiss and Kami Kim (Albert Einstein College of Medicine, Bronx, NY) was held on 23-27 May 2003 in Tarrytown, New York. At this meeting 133 investigators from 14 countries presented 102 papers on research involving this model Apicomplexan parasite. The presented research covered the epidemiology, immunology, cellular biology and molecular biology of this pathogen.

Trans-genera reconstitution and complementation of an adhesion complex in Toxoplasma gondii

Eimeria tenella and Toxoplasma gondii are obligate intracellular parasites belonging to the phylum Apicomplexa. In T. gondii, the microneme protein TgMIC2 contains two well-defined adhesive motifs and is thought to be a key participant in the attachment and invasion of host cells. However, several attempts by different laboratories to generate a knockout (KO) of TgMIC2 have failed, implying that TgMIC2 is an essential gene. As Eimeria and Toxoplasma utilize the same mechanisms of invasion and have highly conserved adhesive proteins, we hypothesized that the orthologous molecule in Eimeria, EtMIC1, could functionally substitute in Toxoplasma to allow a knockout of TgMIC2. TgMIC2 is partnered with a protein called TgM2AP, which corresponds to EtMIC2 in Eimeria. Because the activity of TgMIC2 is most likely tightly linked to its association with TgM2AP, it was thought that the activity of EtMIC1 might similarly require its partner EtMIC2. EtMIC1 and EtMIC2 were introduced into T. gondii, and the presence of EtMIC1 allowed the first knockout clone of TgMIC2 to be obtained. The TgMIC2 KO resulted in significantly decreased numbers of invaded parasites compared to the parental clone. In the absence of TgMIC2, TgM2AP was incorrectly processed and mistargeted to the parasitophorous vacuole instead of the micronemes. These findings indicate that the EtMIC1 can compensate for the essential requirement of TgMIC2, but it cannot fully functionally substitute for TgMIC2 in the invasion process or for supporting the correct maturation and targeting of TgM2AP.

From cells to signaling cascades: manipulation of innate immunity by Toxoplasma gondii

The intracellular opportunistic protozoan Toxoplasma gondii is a potent stimulus for cell-mediated immunity, and IL-12-dependent IFN-gamma induction is vital in resistance to the parasite. Dendritic cells, neutrophils and macrophages are important sources of IL-12 during infection. T. gondii possesses two mechanisms for triggering IL-12. One is dependent upon the common adaptor protein MyD88, and is likely to involve Toll-like receptors. The other is a more unusual pathway that involves triggering through CCR5 by a parasite cyclophilin molecule. Countering these potent pro-inflammatory activities, T. gondii has several mechanisms to down-regulate immunity. Intracellular infection causes a blockade in the NFkappaB macrophage signaling pathway, correlating with reduced capacity for IL-12 and TNF-alpha production. The parasite also prevents STAT1 activity, resulting in decreased levels of IFN-gamma-stimulated MHC surface antigen expression. Furthermore, infection also induces resistance to apoptosis through inhibition of caspase activity. Extracellular pathways of suppression involve soluble mediators such as IL-10 and lipoxins that have potent IL-12 down-regulatory effects. The balance of pro-inflammatory and anti-inflammatory signaling which T. gondii engages is likely dictated by requirements for a stable host-parasite interaction. First, there is a need for Toxoplasma to induce an immune response robust enough to allow host survival and establish long-term chronic infection. Second, the parasite must avoid immune-elimination and induction of pro-inflammatory pathology that can cause lethality if unchecked. The widespread distribution of T. gondii and the normally innocuous nature of infection indicate the skill with which the parasite achieves the two seemingly contrary goals.

Histone H3 and H3.3 variants in the protozoan pathogens Plasmodium falciparum and Toxoplasma gondii

Histones constitute the fundamental component of chromatin and participate in the regulation of gene expression by virtue of covalent modifications to their N-terminal domains. The discovery that histone-modifying enzymes are targeted by the antiprotozoal agent apicidin has prompted further investigation of gene expression regulation in protozoan parasites; consequently, several chromatin remodeling homologues with unusual features have been isolated. To facilitate investigation of these chromatin remodeling homologues using parasite-specific substrates, we sought to clone and characterize histone H3 from two medically significant pathogens in the phylum Apicomplexa: Plasmodium falciparum (malaria) and Toxoplasma gondii (opportunistic pathogen of immunocompromised individuals). Like most eukaryotic organisms, these parasites each contain at least two histone H3 variants, termed H3 and H3.3. Sequence analysis reveals the Apicomplexan H3 proteins harbor novel and rare features. Expression and purification of recombinant H3 variants will provide species-specific substrate for the analysis of the histone-modifying machinery of these parasites.

Dinitroanilines bind alpha-tubulin to disrupt microtubules

Protozoan parasites are remarkably sensitive to dinitroanilines such as oryzalin, which disrupt plant but not animal microtubules. To explore the basis of dinitroaniline action, we isolated 49 independent resistant Toxoplasma gondii lines after chemical mutagenesis. All 23 of the lines that we examined harbored single point mutations in alpha-tubulin. These point mutations were sufficient to confer resistance when transfected into wild-type parasites. Several mutations were in the M or N loops, which coordinate protofilament interactions in the microtubule, but most of the mutations were in the core of alpha-tubulin. Docking studies predict that oryzalin binds with an average affinity of 23 nM to a site located beneath the N loop of Toxoplasma alpha-tubulin. This binding site included residues that were mutated in several resistant lines. Moreover, parallel analysis of Bos taurus alpha-tubulin indicated that oryzalin did not interact with this site and had a significantly decreased, nonspecific affinity for vertebrate alpha-tubulin. We propose that the dinitroanilines act through a novel mechanism, by disrupting M-N loop contacts. These compounds also represent the first class of drugs that act on alpha-tubulin function.

Apicoplast fatty acid biosynthesis as a target for medical intervention in apicomplexan parasites

New chemotherapies for human and animal apicomplexan infections are needed as a component of future strategies to deal with these diseases. An extensive search for new treatments exploring the unique developmental physiology, metabolism and molecular structures of Apicomplexa is under way. The description of the full complement of about 5,300 Plasmodium falciparum genes and fast growing sequence databases for other Apicomplexa allow reconstruction of metabolic pathways of these parasites and thus accelerate identification and biochemical analysis of potential targets. The apicoplast de novo fatty acid biosynthetic pathway shows great potential as a target for small-molecule inhibitors in a stand-alone or combination chemotherapy. Three enzymatic activities, acetyl-CoA carboxylase, beta-ketoacyl-ACP synthase and enoyl-ACP reductase, respond to inhibitors previously identified for bacteria and plants, and deserve to be explored in depth. In this connection, screening systems have been established to seek more potent and specific antiparasitic compounds that are harmless to the host. To this end the interconnections of fatty acid biosynthesis in Apicomplexa with other metabolic and cellular processes must be investigated.