Toxoplasma gondii infection and cerebral toxoplasmosis in HIV-infected patients

Functional dissection of Toxoplasma gondii perforin-like protein 1 reveals a dual domain mode of membrane binding for cytolysis and parasite egress

The recently discovered role of a perforin-like protein (PLP1) for rapid host cell egress by the protozoan parasite Toxoplasma gondii expanded the functional diversity of pore-forming proteins. Whereas PLP1 was found to be necessary for rapid egress and pathogenesis, the sufficiency for and mechanism of membrane attack were yet unknown. Here we further dissected the PLP1 knock-out phenotype, the mechanism of PLP1 pore formation, and the role of each domain by genetic complementation. We found that PLP1 is sufficient for membrane disruption and has a conserved mechanism of pore formation through target membrane binding and oligomerization to form large, multimeric membrane-embedded complexes. The highly conserved, central MACPF domain and the β-sheet-rich C-terminal domain were required for activity. Loss of the unique N-terminal extension reduced lytic activity and led to a delay in rapid egress, but did not significantly decrease virulence, suggesting that small amounts of lytic activity are sufficient for pathogenesis. We found that both N- and C-terminal domains have membrane binding activity, with the C-terminal domain being critical for function. This dual mode of membrane association may promote PLP1 activity and parasite egress in the diverse cell types in which this parasite replicates.

Immunodiagnosis of CNS parasitic infections

The nature of many parasitic infections of the central nervous system (CNS) requires immunodiagnosis to confirm presumptive diagnoses. The CNS is the primary site of parasite infection for some parasitic organisms and for others, neurological infection occurs only in immunocompromised hosts. Still other parasites cause ectopic infections of the CNS and occur very rarely. This review concentrates on laboratory diagnosis of diseases that are caused by parasites with a primary predilection for the CNS. Emphasis is placed on laboratory diagnostic methods that are used and suitable for clinical diagnosis, rather than a comprehensive review of all the experimental methods that have been reported in the literature. Immunodiagnosis is not appropriate for the diagnosis of all parasitic infections of the CNS; in those cases, alternative diagnostic methods are presented, but not discussed in detail. In some instances potential new antigens or methods are presented, particularly if adoption of these methods is expected in the near future.

Toxoplasmosis

Toxoplasma gondii, an Apicomplexan, is a pathogic protozoan that can infect the central nervous system. Infection during pregnancy can result in a congenial infection with severe neurological sequelae. In immunocompromised individuals reactivation of latent neurological foci can result in encephalitis. Immunocompetent individuals infected with T. gondii are typically asymptomatic and maintain this infection for life. However, recent studies suggest that these asymptomatic infections may have effects on behavior and other physiological processes. Toxoplasma gondii infects approximately one-third of the world population, making it one of the most successful parasitic organisms. Cats and other felidae serve as the definite host producing oocysts, an environmentally resistant life cycle stage found in cat feces, which can transmit the infection when ingested orally. A wide variety of warm-blooded animals, including humans, can serve as the intermediate host in which tissue cysts (containing bradyzoites) develop. Transmission also occurs due to ingestion of the tissue cysts. There are three predominant clonal lineages, termed Types I, II and III, and an association with higher pathogenicity with the Type I strains in humans has emerged. This chapter presents a review of the biology of this infection including the life cycle, transmission, epidemiology, parasite strains, and the host immune response. The major clinical outcomes of congenital infection, chorioretinitis and encephalitis, and the possible association of infection of toxoplasmosis with neuropsychiatric disorders such as schizophrenia, are reviewed.

Immunization with excreted/secreted proteins in AS/n mice activating cellular and humoral response against Toxoplasma gondii infection

This study investigated how Toxoplasma gondii excretory-secretory antigens (ESA) stimulate the humoral and cellular response in infected hosts. We evaluated IFN-γ, IL-4 TNF-α, and IL-10 levels as well as humoral response of ESA-immunized AS/n mice. T. gondii lysate antigen (TLA), a crude antigen, was used in all experiments to evaluate the immune response. Chronic infected and naive mice were used as control groups, since the immune response is well known. The challenge experiments showed the parasitemia levels, determined by real time PCR and survival index. The naive group had early mortality and higher parasitemia than the ESA-immunized mouse group. In addition the chronic infected group had no parasitemia and mortality. Both ESA-immunized and chronic infected mice produced a similar level of IFN-γ and TNF-α. ESA, also, activated cells from immunized mice to produce IL-4 and IL-10 in lower levels compared to those cells collected from chronic mice but sufficient to modulate IFN-γ and TNF-α synthesis, preventing an excessive immune response that could cause extensive inflammation and host tissue damage. After 6 weeks, ESA-immunized mice had low IgM and IgG2a levels and high IgG1 levels. Purified anti-ESA IgG were able to opsonize tachyzoites (RH strain), and mice that received these parasites had lower parasitemia, and mortality was delayed 48 h, compared with the same results from those receiving parasites opsonized with IgG purified from naive mice. The protective immune response in the chronic infection was efficient in protecting the host against infection caused by other T. gondii strain and ESA participate in stimulating the host humoral and cellular responses. The immunization assays showed that ESA can elicit high IgG1, IFN-γ and TNF-α production and, a lower amount of IgM, IgG2, IL-10 and IL-4, suggesting a mixed Th1/Th2 profile.

Toxoplasma gondii Myocarditis after Adult Heart Transplantation: Successful Prophylaxis with Pyrimethamine

Toxoplasma gondii primary infection/reactivation after solid organ transplantation is a serious complication, due to the high mortality rate following disseminated disease. We performed a retrospective study of all cases of T. gondii infections in 436 adult patients who had received an orthotopic cardiac transplant at our Institution from May 1968 to January 2011. Six patients (1.3%) developed T. gondii infection/reactivation in the post-operative period. All infections/reactivations occurred before 1996, when no standardized toxoplasmosis prophylactic regimen or co-trimoxazole prophylaxis was used. Starting with the 112th heart transplant, oral pyrimethamine 75 mg/day was used for seronegative transplant recipients whose donors were seropositive or unknown. Two patients (33.3%) presented with disseminated toxoplasmosis infection, and all patients (100%) had myocarditis. Five patients (83.3%) were seronegative before transplant and one patient did not have pre-transplant serology available. Median time for infection onset was 131 days following transplantation. Three patients (50%) died due to toxoplasmosis infection. After 1996, we did not observe any additional cases of T. gondii infection/reactivation. In conclusion, toxoplasmosis in heart allographs was more frequent among seronegative heart recipients, and oral pyrimethamine was highly effective for the prevention of T. gondii infection in this population.

Toxoplasmosis in humans and animals in Brazil: high prevalence, high burden of disease, and epidemiology

Infections by the protozoan parasite Toxoplasma gondii are widely prevalent in humans and animals in Brazil. The burden of clinical toxoplasmosis in humans is considered to be very high. The high prevalence and encouragement of the Brazilian Government provides a unique opportunity for international groups to study the epidemiology and control of toxoplasmosis in Brazil. Many early papers on toxoplasmosis in Brazil were published in Portuguese and often not available to scientists in English-speaking countries. In the present paper we review prevalence, clinical spectrum, molecular epidemiology, and control of T. gondii in humans and animals in Brazil. This knowledge should be useful to biologists, public health workers, veterinarians, and physicians. Brazil has a very high rate of T. gondii infection in humans. Up to 50% of elementary school children and 50-80% of women of child-bearing age have antibodies to T. gondii. The risks for uninfected women to acquire toxoplasmosis during pregnancy and fetal transmission are high because the environment is highly contaminated with oocysts. The burden of toxoplasmosis in congenitally infected children is also very high. From limited data on screening of infants for T. gondii IgM at birth, 5-23 children are born infected per 10 000 live births in Brazil. Based on an estimate of 1 infected child per 1000 births, 2649 children with congenital toxoplasmosis are likely to be born annually in Brazil. Most of these infected children are likely to develop symptoms or signs of clinical toxoplasmosis. Among the congenitally infected children whose clinical data are described in this review, several died soon after birth, 35% had neurological disease including hydrocephalus, microcephaly and mental retardation, 80% had ocular lesions, and in one report 40% of children had hearing loss. The severity of clinical toxoplasmosis in Brazilian children may be associated with the genetic characteristics of T. gondii isolates prevailing in animals and humans in Brazil.

Prevalence and genotypes of Toxoplasma gondii in pork from retail meat stores in Eastern China

Pork is known as one of the most important sources of Toxoplasma gondii infection in China. In the present study, 416 fresh pork samples were collected from different locations of Anhui province, Eastern China. Tissue fluid ELISA was conducted to detect the antibodies to T. gondii. Real-time PCR and bioassay were performed to identify the presence of T. gondii DNA and viable parasites, respectively. Seventy-five out of 416 samples (18.03%) demonstrated real-time PCR positive reaction and 42 out of 416 samples (10.1%) showed tissue fluid ELISA positive reaction. One isolate (Tgpkfx171) was obtained through bioassay in mice from 14 samples that demonstrated both PCR and ELISA positive reaction. The isolate and seven positive DNA samples were genotyped using 9 PCR-RFLP markers including SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico. Among these, only the isolate and two positive DNA samples were genotyped with complete data for all loci, belonging to ToxoDB#9 (Chinese 1) and ToxoDB#213, respectively. This is the first report of the prevalence and genetic typing of T. gondii from pork in retail meat stores in China. The present results provide an accurate picture of the risk of exposure to T. gondii in retail pork in China.

Mechanisms of Toxoplasma gondii persistence and latency

Toxoplasma gondii is an obligate intracellular protozoan parasite that causes opportunistic disease, particularly in immunocompromised individuals. Central to its transmission and pathogenesis is the ability of the proliferative stage (tachyzoite) to convert into latent tissue cysts (bradyzoites). Encystment allows Toxoplasma to persist in the host and affords the parasite a unique opportunity to spread to new hosts without proceeding through its sexual stage, which is restricted to felids. Bradyzoite tissue cysts can cause reactivated toxoplasmosis if host immunity becomes impaired. A greater understanding of the molecular mechanisms orchestrating bradyzoite development is needed to better manage the disease. Here, we will review key studies that have contributed to our knowledge about this persistent form of the parasite and how to study it, with a focus on how cellular stress can signal for the reprogramming of gene expression needed during bradyzoite development.

Passage of parasites across the blood-brain barrier

The blood-brain barrier (BBB) is a structural and functional barrier that protects the central nervous system (CNS) from invasion by blood-borne pathogens including parasites. However, some intracellular and extracellular parasites can traverse the BBB during the course of infection and cause neurological disturbances and/or damage which are at times fatal. The means by which parasites cross the BBB and how the immune system controls the parasites within the brain are still unclear. In this review we present the current understanding of the processes utilized by two human neuropathogenic parasites, Trypanosoma brucei spp and Toxoplasma gondii, to go across the BBB and consequences of CNS invasion. We also describe briefly other parasites that can invade the brain and how they interact with or circumvent the BBB. The roles played by parasite-derived and host-derived molecules during parasitic and white blood cell invasion of the brain are discussed.

Importance of high IgG anti-Toxoplasma gondii titers and PCR detection of T. gondii DNA in peripheral blood samples for the diagnosis of AIDS-related cerebral toxoplasmosis: a case-control study

BACKGROUND

Cerebral toxoplasmosis (CT) continues to cause significant morbidity and mortality in human immunodeficiency virus (HIV)-infected patients in Brazil. In clinical practice, the initial diagnosis is usually presumptive and alternative diagnosis tools are necessary. Our objective was to evaluate whether the detection of high titers of IgG anti-Toxoplasma gondii and T. gondii DNA in blood samples are associated with the diagnosis of CT.

METHODS

In this case-control study we included 192 patients with HIV-1 infection: 64 patients with presumptive CT (cases) and 128 patients with other diseases (controls). Blood samples to perform indirect immunofluorescense reaction (IFI) to detect anti-T. gondii IgG antibodies and polymerase chain reaction (PCR) were collected before or within the first three days of anti-Toxoplasma therapy. Two multivariate logistic regression models were performed: one including the variable qualitative serology and another including quantitative serology.

RESULTS

In the first model, positive IgG anti-T. gondii (OR 4.7, 95% CI 1.2-18.3; p = 0.027) and a positive T. gondii PCR result (OR 132, 95% CI 35-505; p < 0.001) were associated with the diagnosis. In the second model, IgG anti-T. gondii titres > 1:1024 (OR 7.6, 95% CI 2.3-25.1; p = 0.001) and a positive T. gondii PCR result (OR 147, 95% CI 35-613; p < 0.001) were associated with the diagnosis.

CONCLUSIONS

Quantitative serology and molecular diagnosis in peripheral blood samples were independently associated with the diagnosis of CT in HIV-infected patients. These diagnostic tools can contribute to a timely diagnosis of CT in settings where Toxoplasma infection is common in the general population.

Toxoplasma gondii antigens: recovery analysis of tachyzoites cultivated in Vero cell maintained in serum free medium

Vero cells have been used successfully in Toxoplasma gondii maintenance. Medium supplementation for culture cells with fetal bovine serum is necessary for cellular growth. However, serum in these cultures presents disadvantages, such as the potential to induce hypersensitivity, variability of serum batches, possible presence of contaminants, and the high cost of good quality serum. Culture media formulated without any animal derived components, designed for serum-free growth of cell lines have been used successfully for different virus replication. The advantages of protozoan parasite growth in cell line cultures using serum-free medium remain poorly studied. Thus, this study was designed to determine whether T. gondii tachyzoites grown in Vero cell cultures in serum-free medium, after many passages, are able to maintain the same antigenic proprieties as those maintained in experimental mice. The standardization of Vero cell culture in serum-free medium for in vitro T. gondii tachyzoite production was performed establishing the optimal initial cell concentration for the confluent monolayer formation, which was 1×10(6) Vero cell culture as initial inoculum. The total confluent monolayer formatted after 96 h and the best amount of harvested tachyzoites was 2.1×10(7) using parasite inoculum of 1.5×10(6) after 7 days post-infection. The infectivity of tachyzoites released from Vero cells maintained in serum-free medium was evaluated using groups of Swiss mice infected with cell-culture tachyzoites. The parasite concentrations were similar to those for mice infected with tachyzoites collected from other infected mice. The data from both in vivo and in vitro experiments showed that in at least 30 culture cell passages, the parasites maintained the same infectivity as maintained in vivo. Another question was to know whether in the several continued passages, immunogenic progressive loss could occur. The nucleotide sequences studied were the same between the different passages, which could mean no change in their viability in the lysate antigen. Thus, the antigen production by cell culture has clear ethical and cost-saving advantages. Moreover, the use of culture media formulated without any human or animal derived components, designed for serum-free growth of cell lines, successfully produced tachyzoites especially for antigen production.

Parasitic infections in HIV infected individuals: diagnostic & therapeutic challenges

After 30 years of the human immunodeficiency virus (HIV) epidemic, parasites have been one of the most common opportunistic infections (OIs) and one of the most frequent causes of morbidity and mortality associated with HIV-infected patients. Due to severe immunosuppression, enteric parasitic pathogens in general are emerging and are OIs capable of causing diarrhoeal disease associated with HIV. Of these, Cryptosporidium parvum and Isospora belli are the two most common intestinal protozoan parasites and pose a public health problem in acquired immunodeficiency syndrome (AIDS) patients. These are the only two enteric protozoan parasites that remain in the case definition of AIDS till today. Leishmaniasis, strongyloidiasis and toxoplasmosis are the three main opportunistic causes of systemic involvements reported in HIV-infected patients. Of these, toxoplasmosis is the most important parasitic infection associated with the central nervous system. Due to its complexity in nature, toxoplasmosis is the only parasitic disease capable of not only causing focal but also disseminated forms and it has been included in AIDS-defining illnesses (ADI) ever since. With the introduction of highly active anti-retroviral therapy (HAART), cryptosporidiosis, leishmaniasis, schistosomiasis, strongyloidiasis, and toxoplasmosis are among parasitic diseases reported in association with immune reconstitution inflammatory syndrome (IRIS). This review addresses various aspects of parasitic infections in term of clinical, diagnostic and therapeutic challenges associated with HIV-infection.

The adaptive potential of a survival artist: characterization of the in vitro interactions of Toxoplasma gondii tachyzoites with di-cationic compounds in human fibroblast cell cultures

The impact of di-cationic pentamidine-analogues against Toxoplama gondii (Rh- and Me49-background) was investigated. The 72 h-growth assays showed that the arylimidamide DB750 inhibited the proliferation of tachyzoites of T. gondii Rh and T. gondii Me49 with an IC(50) of 0·11 and 0·13 μM, respectively. Pre-incubation of fibroblast monolayers with 1 μM DB750 for 12 h and subsequent culture in the absence of the drug also resulted in a pronounced inhibiton of parasite proliferation. However, upon 5-6 days of drug exposure, T. gondii tachyzoites adapted to the compound and resumed proliferation up to a concentration of 1·2 μM. Out of a set of 32 di-cationic compounds screened for in vitro activity against T. gondii, the arylimidamide DB745, exhibiting an IC(50) of 0·03 μM and favourable selective toxicity was chosen for further studies. DB745 also inhibited the proliferation of DB750-adapted T. gondii (IC(50)=0·07 μM). In contrast to DB750, DB745 also had a profound negative impact on extracellular non-adapted T. gondii tachyzoites, but not on DB750-adapted T. gondii. Adaptation of T. gondii to DB745 (up to a concentration of 0·46 μM) was much more difficult to achieve and feasible only over a period of 110 days. In cultures infected with DB750-adapted T. gondii seemingly intact parasites could occasionally be detected by TEM. This illustrates the astonishing capacity of T. gondii tachyzoites to adapt to environmental changes, at least under in vitro conditions, and suggests that DB745 could be an interesting drug candidate for further assessments in appropriate in vivo models.

Contribution of laboratory methods in diagnosing clinically suspected ocular toxoplasmosis in Brazilian patients

This prospective study evaluated the value of laboratorial diagnosis in ocular toxoplasmosis analyzing peripheral blood samples from a group of Brazilian patients by immunologic and molecular methods. We analyzed blood samples from 184 immunocompetent patients with ocular disorders divided into 2 groups: Group I, composed of samples from 49 patients with ocular toxoplasmosis diagnosed by clinical features; Group II, samples from 135 patients with other ocular diseases. Samples were assayed by conventional polymerase chain reaction (cnPCR), real-time PCR (qPCR) for Toxoplasma gondii, indirect immunofluorescence reaction (IF), avidity test (crude tachyzoite lysate as antigen), and excreted-secreted tachyzoite proteins as antigen (ESA-ELISA). cnPCR and qPCR profiles were concordant in all samples. Positive PCR was shown in 40.8% of group I patients. The majority of the positive blood samples (75%) were taken from patients with toxoplasmic retinochoroiditis scars, and the others (25%), from patients with retinal exudative lesions. Despite that 86 of the 135 patients from Group II had asymptomatic toxoplasmosis, all DNA blood samples had negative PCR. Concordant results were shown in the data obtained by serologic methods. Around 24% of the patients with ocular toxoplasmosis had high antibody titers determined by ESA-ELISA and IF. Anti-ESA antibodies are shown principally in patients with active infection. Collectively, these data demonstrate the presence of tachyzoites in the blood of patients with chronic infection, supporting the idea of recurrent disease. Circulating parasites in blood of immunocompetent individuals may be associated with the reactivation of the ocular disease.

Importance of nonenteric protozoan infections in immunocompromised people

There are many neglected nonenteric protozoa able to cause serious morbidity and mortality in humans, particularly in the developing world. Diseases caused by certain protozoa are often more severe in the presence of HIV. While information regarding neglected tropical diseases caused by trypanosomatids and Plasmodium is abundant, these protozoa are often not a first consideration in Western countries where they are not endemic. As such, diagnostics may not be available in these regions. Due to global travel and immigration, this has become an increasing problem. Inversely, in certain parts of the world (particularly sub-Saharan Africa), the HIV problem is so severe that diseases like microsporidiosis and toxoplasmosis are common. In Western countries, due to the availability of highly active antiretroviral therapy (HAART), these diseases are infrequently encountered. While free-living amoebae are rarely encountered in a clinical setting, when infections do occur, they are often fatal. Rapid diagnosis and treatment are essential to the survival of patients infected with these organisms. This paper reviews information on the diagnosis and treatment of nonenteric protozoal diseases in immunocompromised people, with a focus on patients infected with HIV. The nonenteric microsporidia, some trypanosomatids, Toxoplasma spp., Neospora spp., some free-living amoebae, Plasmodium spp., and Babesia spp. are discussed.

Real-time quantitative PCR in cerebral toxoplasmosis diagnosis of Brazilian human immunodeficiency virus-infected patients

Cerebral toxoplasmosis is the most common cerebral mass lesion in AIDS patients in Brazil, and results in high mortality and morbidity, despite free access to HAART (highly active antiretroviral treatment). Molecular diagnosis based on conventional PCR (cnPCR) or real-time quantitative PCR (qrtPCR) has been indispensable for definitive diagnosis. We report here the evaluation of qrtPCR with blood and cerebrospinal fluid (CSF) samples from AIDS patients in Brazil. This prospective study was conducted for 2 years, analysing DNA samples extracted from 149 AIDS patients (98 blood and 51 CSF samples) with confirmed clinical and radiological diagnosis. The laboratory diagnosis included cnPCR (with the B22/B23 primer set) and indirect immunofluorescence (IF). For qrtPCR, two primer sets were simultaneously designed based on described genes and using a 6-carboxyfluorescein dye-labelled TaqMan MGB (minor groove binder) probe. One was B1Tg, which amplified a sequence from the B1 gene. The other was the RETg, which amplified a PCR product of the 529 bp sequence. The overall cnPCR and qrtPCR results were: positive results were observed in 33.6% (50) patients. The sensitivities were 98% for cnPCR (B22/B23), and 86 and 98% for qrtPCR (B1Tg and RETg, respectively). Negative reactions were observed in 66.4% patients. The specificities were 97% for cnPCR and qrtPCR (B1Tg), and 88.8 % for RETg. These data show that RETg PCR is highly sensitive as it amplifies a repeat region with many copies; however, its specificity is lower than the other markers. However, B1Tg PCR had good specificity, but lower sensitivity. Among the patients, 20 had blood and CSF collected simultaneously. Thus, their results permitted us to analyse and compare molecular, serological and clinical diagnosis for a better understanding of the different scenarios of laboratorial and clinical diagnosis. For nine patients with confirmed cerebral toxoplasmosis diagnosis, four scenarios were observed: (i) and (ii) negative molecular diagnosis for CSF and positive for blood with variable IF titres for the sera and CSF (negative or positive); (iii) positive molecular diagnosis with CSF and negative with blood; and (iv) positive molecular diagnosis in both samples. In the latter two situations, normally the IF titres in sera and CSF are variable. Other opportunistic infections were shown in 11 patients. Despite the IF titres in sera and CSF being variable, all of them had negative molecular diagnosis for both samples. qrtPCR allows for a rapid identification of Toxoplasma gondii DNA in patient samples; in a minority of cases discrepancies occur with the cnPCR.