Ocular toxoplasmosis: an update and review of the literature

Prevalence of toxoplasmosis and related risk factors among humans referred to main laboratories of Urmia city, North West of Iran, 2013

Toxoplasmosis is mostly asymptomatic infection in immunocompetent individuals while it can cause a severe infection in human fetus during pregnancy and immunocompromised patients. This study aimed to determine the prevalence of anti-Toxoplasma IgM and IgG seropositivity and potential risk factors of the infection in humans referred to Urmia City main diagnostic laboratories, Urmia, Iran. Totally 195 blood samples were collected from the individuals referred to main diagnostic laboratories of Urmia City, 2013. Serum concentration of anti-Toxoplasma IgG and IgM were determined using ELISA method. Demographic variables of the participants were collected by interviewing, which are including sex, age, occupation, educational and residential status, eating undercooked meat, consumption of raw vegetable and the method of washing raw vegetables. None of all 200 serum sample were anti-Toxoplasma IgM positive, but different concentrations of anti-Toxoplasma IgG were observed in 88 (45.12 %) of samples. The significant higher rate of anti-Toxoplasma IgG seropositivity were observed in people with soil related jobs (P = 0.005, OR = 2.266; 95 % CI 1.260, 4.078) and history of eating raw vegetables at restaurant (P = 0.036, OR = 1.985; 95 % CI 0.991, 3.978). Also anti-Toxoplasma IgG concentration mean was significantly higher in people who were commonly eaten raw vegetable at restaurants (P < 0.001, t = 7.918). The prevalence of chronic toxoplasmosis is considerably high while the acute infection is very low in the studied area. Having soil related jobs and eating raw vegetables at restaurants increases the risk of acquiring the infection.

Trimethoprim-sulfamethoxazole versus placebo to reduce the risk of recurrences of Toxoplasma gondii retinochoroiditis: randomized controlled clinical trial

PURPOSE

To compare the effects of trimethoprim-sulfamethoxazole vs placebo in reducing the risk of recurrences of Toxoplasma gondii retinochoroiditis.

DESIGN

Single-center, prospective randomized double-masked clinical trial.

METHODS

A total of 95 patients from Campinas, Brazil, with active recurrent Toxoplasma gondii retinochoroiditis were included. The initially active toxoplasmosis lesions were successfully treated in all cases using trimethoprim-sulfamethoxazole (800 mg/160 mg) twice daily for 45 days. Subsequently, 5 patients dropped out of the study. The remaining patients were randomized to Group 1 (trimethoprim/sulfamethoxazole tablet every 2 days) or Group 2 (identical placebo tablet every 2 days). Randomization was 1:1, was stratified by sex, and used block sizes of 4. The primary outcome was recurrent toxoplasmosis retinochoroiditis within 1 year, and the secondary outcome was a 1-year change in best-corrected visual acuity (BCVA) (ETDRS chart).

RESULTS

The incidence of recurrent toxoplasmosis retinochoroiditis within 12 months was 0 of 46 (0%) and 6 of 47 (12.80%) in the trimethoprim-sulfamethoxazole and placebo groups, respectively (P = .026). Visual acuity improvements in the 2 groups were similar. No treatment-limiting toxicity was observed.

CONCLUSIONS

Trimethoprim/sulfamethoxazole therapy resulted in a 100% reduction in the recurrence of Toxoplasma gondii retinochoroiditis over 1 year of treatment.

Patients with diffuse uveitis and inactive toxoplasmic retinitis lesions test PCR positive for Toxoplasma gondii in their vitreous and blood

BACKGROUND/AIMS

To determine if patients with inactive chorioretinitis lesions who experience chronic toxoplasmic uveitis test PCR positive for Toxoplasma in their ocular fluids.

METHODS

Two patients undergoing long-term anti-toxoplasmic treatment developed chronic uveitis and vitritis. They underwent therapeutic and diagnostic pars plana vitrectomy. Patient specimens were tested for toxoplasmosis by real-time PCR and nested PCR. Patient specimens were also tested for the presence of Toxoplasma antibodies that recognise allelic peptide motifs to determine parasite serotype.

RESULTS

Patients tested positive for Toxoplasma by real-time PCR at the B1 gene in the vitreous and aqueous humours of patient 1, but only the vitreous of patient 2. Patients were not parasitemic by real-time PCR in plasma and blood. During surgery, only old hyperpigmented toxoplasmic scars were observed; there was no sign of active retinitis. Multilocus PCR-DNA sequence genotyping at B1, NTS2 and SAG1 loci established that two different non-archetypal Toxoplasma strains had infected patients 1 and 2. A peptide-based serotyping ELISA confirmed the molecular findings.

CONCLUSIONS

No active lesions were observed, but both patients possessed sufficient parasite DNA in their vitreous to permit genotyping. Several hypotheses to explain the persistence of the vitritis and anterior uveitis in the absence of active retinitis are discussed.

Incidence of Toxoplasma retinochoroiditis in patients with ankylosing spondylitis after using TNF-α blockers

TNF-α blockers are associated with reactivation of latent granulomatous infections and almost 6% of the world population has some chorioretinitis (CR) caused by Toxoplasma gondii. Thus, the blockade of TNF-α could reactivate a latent toxoplasmosis infection (LTxI). This study was conducted to evaluate the prevalence and incidence of chronic and active CR related to T. gondii in patients with ankylosing spondylitis (AS). A total of 74 eyes from 37 active AS outpatients starting TNFα blockers were compared with 35 AS patients, matched to age and sex, under conventional therapy in a prospective and controlled trial. All patients underwent serological tests for T. gondii, as well as periodic ophthalmologic examination during 12months. Active CR was defined if a white, focal retinochoroidal lesion with overlying vitreous inflammation had been found. Retinochoroidal lesions with sharp edges, hyperpigmented borders and atrophic center were defined as CR scars. At baseline, no patient had active CR. From the 144 eyes examined, almost 6% had CR scars and only 2.1% had a typical toxoplasmic CR scar and all of them were negative for HLA-B27. During 12months of follow-up, no recurrence or new CR were observed. AS patients using TNF-α blockers do not have a higher risk of acute or chronic CR caused by T. gondii.

IL-10 reduces levels of apoptosis in Toxoplasma gondii-infected trophoblasts

Background

To analyze the effects of IL-10 on the HLA-G expression and the apoptosis of trophoblasts infected with Toxoplasma gondii.

Methods

T. gondii-infected or uninfected human trophoblasts and immortalized human placental BeWo cells were cultured with or without human IL-10. Uninfected and infected cells without IL-10 cells served as controls. HLA-G expression was measured by real-time PCR and flow cytometry, respectively. Cells apoptosis were analyzed by flow cytometry. Apoptosis associated moleculars were measured by real-time PCR and Western bolt.

Results

HLA-G expression was increased in the infected trophoblasts and BeWo cells compared to uninfected cells. Treatment of infected cells with IL-10 decreased HLA-G expression compared to infected cells while no change in treatment of uninfected cells compared with uninfected cells. Levels of apoptosis and apoptosis associated caspase-3 and caspase-8 decreased and c-FLIP levels increased in treated infected cells with IL-10 compared to infected cells and no difference in IL-10 treated uninfected cells compared to uninfected cells.

Conclusions

IL-10 regulates HLA-G expression in T. gondii-infected trophoblasts. IL-10 treatment of infected trophoblasts reduced levels of apoptosis. This may contribute to the improvement in pregnancy outcomes when women infected with T. gondii treated with IL-10.

Acute toxoplasmosis mimicking melanoma metastases: review of conditions causing false-positive results on (18)F-FDG PET/CT

Invasive malignant melanoma is the most common fatal form of skin cancer. Fluorine-18-fluorodeoxyglucose positron emission tomography-computed tomography demonstrates a very high sensitivity and specificity for the detection of melanoma metastases. Here, we report an unusual case of toxoplasma lymphadenitis in a male adult patient mimicking a malignant cervical lymphadenopathy. Toxoplasmosis is a zoonosis caused by the intracellular parasite Toxoplasma gondii, which is usually asymptomatic in immunocompetent hosts.

Toxoplasma gondii infection regulates the balance of activating and inhibitory receptors on decidual natural killer cells

Inhibitory receptors and activating receptor expressed on decidual natural killer (dNK) cells are generally believed to be important in abnormal pregnancy outcomes and induced adverse pregnancy. However, if Toxoplasma gondii (T. gondii) infection induced abnormal pregnancy was related to dNK cells changes is not clear. In this study, we used human dNK cells co-cultured with human extravillous cytotrophoblast (EVT) cells following YFP-Toxoplasma gondii (YFP-T. gondii) infection in vitro and established animal pregnant infection model. Levels of inhibitory receptors KIR2DL4 and ILT-2, their ligand HLA-G, and activating receptor NKG2D in human decidua, and NKG2A and its ligand Qa-1 and NKG2D in mice uterine were analyzed by real-time PCR and flow cytometry with levels of NKG2D significantly higher than those of KIR2DL4 and ILT-2 in vitro and in invo. The level of NKG2D was positively correlated with cytotoxic activity of dNK cells in vitro. Numbers of abnormal pregnancies were significantly greater in the infected group than in the control group. This result demonstrated that the increased NKG2D expression and imbalance between inhibitory receptors of dNK cells and HLA-G may contribute to abnormal pregnancy outcomes observed upon maternal infection with T. gondii.

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.

Toxoplasma gondii: the effect of fluconazole combined with sulfadiazine and pyrimethamine against acute toxoplasmosis in murine model

Toxoplasma gondii is an important opportunistic pathogen for immunocompromised patients and responsible for toxoplasmic encephalitis, which is often lethal. Treatment for this infection is limited to a restricted therapeutic arsenal. In this work we tested the combination of fluconazole with the current treatment for acute toxoplasmosis on the murine model in vivo. Different experimental groups were treated with combinations of sulfadiazine plus pyrimethamine with fluconazole and pyrimethamine with fluconazole. Fluconazole is an important antifungal triazole used against others CNS related opportunistic pathogens such as Cryptococcus neoformans and Candida spp. The combinations of fluconazole plus sulfadiazine and pyrimethamine or fluconazole plus pyrimethamine were remarkably effective against T. gondii in vivo. The 10-day treatment with 10mg/kg/day of fluconazole combined with 40/1mg/kg/day sulfadiazine and pyrimethamine resulted in 93% survival of CF1 mice acutely infected with the highly virulent T. gondii RH strain, versus 36% of mice treated with just sulfadiazine and pyrimethamine. Combinations of fluconazole with lower doses of sulfadiazine and pyrimethamine or with just pyrimethamine were also efficient in reducing the mortality of mice compared with the treatment without fluconazole. The results obtained are promising for the treatment of human toxoplasmosis and point to the need to extend these studies to other murine models.

Changes of human decidual natural killer cells cocultured with YFP-Toxoplasma gondii: implications for abnormal pregnancy

OBJECTIVE

To investigate the changes of human decidual natural killer (dNK) cells cocultured with Toxoplasma gondii in vitro and to infer implications on pregnancy.

DESIGN

Case-control study.

SETTING

College and hospital.

PATIENT(S)

Decidual tissue was obtained from 85 patients undergoing voluntary abortion during the first trimester of gestation (6-12 weeks).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The dNK cells were isolated and infected with YFP-Toxoplasma gondii. Cells were observed by fluorescence and confocal microscopy. The CD56(bright)CD16(-)/CD56(dim)CD16(+) dNK ratio, expression of KIR2DL4, ILT-2, and NKG2D on dNK cells were analyzed by flow cytometry and the cytotoxic activity of infected dNK cells were evaluated.

RESULT(S)

The CD56(dim)CD16(+)/CD56(bright)CD16(-) dNK ratio was significantly elevated at 12, 24, and 48 hours after YFP-T. gondii infection. Expression of KIR2DL4, ILT-2, and NKG2D were increased after infection, but NKG2D were significantly higher than those of KIR2DL4 and ILT-2. Both the CD56(dim)CD16(+)/CD56(bright)CD16(-) dNK ratio and NKG2D expression were correlated with dNK cytotoxic activity.

CONCLUSION(S)

Enhanced dNK cytotoxicity due to increased CD16 and NKG2D expression may contribute to abnormal pregnancy outcomes observed with maternal infection with T. gondii.

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.

The role of serology in active ocular toxoplasmosis

Our purpose was to examine toxoplasmic serology in relation to episodes of suspected acute toxoplasmic retinochoroiditis and evaluate its use in the appraisal of patients. The mean values of enzymatic immunoassay (EIA) titers for toxoplasmic antibodies were retrospectively compared in patients with active and inactive toxoplasmosis and in a third group of uveitis cases not caused by toxoplasmosis. The proportion of cases under and above a predefined serology value above cut-off was compared in all groups. Between 1995 and 2010, 97 out of 1,276 new uveitis cases seen at the Centre for Ophthalmic Specialized Care (COS), Lausanne, Switzerland were diagnosed as toxoplasmic retinochoroiditis, of which 51 had documented serology available. The mean EIA values for immunoglobulin (Ig) G were 147.75 ± 259.4 IU/ml for patients with active disease, 18.93 ± 23.09 (p < 0.05) for patients with inactive toxoplasmosis and 18.35 ± 20.82 for controls (p < 0.017). The proportion of cases under the designated limit value were 2/51 (4%) in the active retinitinochoroiditis group, 14/27 (52%) (p < 0.05) in the control group, and 7/7 (100%) in the inactive toxoplasmic group (p < 0.001). Three out of 51 cases showed high IgM values in addition to IgG elevation and were primary infections. Toxoplasmosis serology, contrary to popular belief, is useful to confirm active toxoplasmic retinochoroiditis; it is easy to perform, cheap and supports clinical diagnosis in up to 96% of cases, not only by showing positivity but by also showing a significant elevation of titers. In atypical cases serology is not only useful but essential.

Toxoplasmosis: new challenges for an old disease

More than a century after the identification of Toxoplasma gondii, major issues need to be addressed for the optimal management of ocular disease. Toxoplasmic retinochoroiditis is the main cause of posterior uveitis in several geographical areas. The parasite establishes a love-hate relationship with the eye, manipulating the immune response and inducing variable initial lesions and further relapses. It is now well established that most cases are acquired after birth and not congenital. The severity of the disease is mainly due to the parasite genotype and the host immune status. Diagnosis is based on clinical features, but may be confirmed by biological tools applied to ocular fluids. Combining several techniques improves the diagnostic yield in equivocal cases. Therapeutic management is the most important challenge. Even though evidence-based data on the efficacy of anti-parasitic drugs are still missing, new strategies with a good safety profile are available and may be proposed earlier during the course of the disease, but also in selected cases, to reduce sight-threatening relapses. Revisiting the therapeutic options and indications may be an important step towards long-term maintenance of the visual function and avoidance of major complications.

The immunoprotective role of interleukin-10 in abnormal pregnancy outcome induced by Toxoplasma gondii infection

AIMS

To investigate the immunoprotective effect of IL-10 on pregnancy in Toxoplasma gondii-infected C57BL/6 mice.

METHODS

Twenty-four pregnant mice were randomly divided into 3 equal groups, i.e. a control group (CG), an infected group (IG) and an infected group treated with IL-10 (IPTG). Each IPTG and IG mouse was infected with 400 T. gondii trophozoites on gestational day (GD) 8. Each IPTG mouse was injected with 1 μg recombinant mouse IL-10 via a tail vein on GD 10 and 12. The mice were sacrificed on day 7 postinfection. Qa-1 and NKG2A were analyzed in the placenta by flow cytometry and real-time PCR. IL-4, IL-10 and IFN-γ in the placenta supernatant were analyzed by ELISA. Statistical analysis was performed by one-way ANOVA.

RESULTS

IPTG mice showed a better mental state, had larger fetuses and placentas with a better blood supply and a lower resorption ratio compared to IG mice. NKG2A and Qa-1 were significantly increased in IPTG mice compared to IG mice (p < 0.05). IL-4 and IL-10 in IPTG placenta supernatant were increased (p < 0.05), but IFN-γ was decreased (p < 0.05) compared to IG placenta supernatant. The ratios of IFN-γ/IL-4 and IFN-γ/IL-10 were decreased in IPTG mice compared to IG mice (p < 0.05, p < 0.05).

CONCLUSION

IL-10 plays an immunoprotective role and improves the pregnancy outcome of T. gondii-infected mice.

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.

Phosphodiesterase inhibitors as a new generation of antiprotozoan drugs: exploiting the benefit of enzymes that are highly conserved between host and parasite

Protozoan infections remain a major unsolved medical problem in many parts of our world. A major obstacle to their treatment is the blatant lack of medication that is affordable, effective, safe and easy to administer. For some of these diseases, including human sleeping sickness, very few compounds are available, many of them old and all of them fraught with toxic side effects. We explore a new concept for developing new-generation antiprotozoan drugs that are based on phosphodiesterase (PDE) inhibitors. Such inhibitors are already used extensively in human pharmacology. Given the high degree of structural similarity between the human and the protozoan PDEs, the vast expertise available in the human field can now be applied to developing disease-specific PDE inhibitors as new antiprotozoan drugs.

Toxoplasma gondii protects against H(2)O(2) -induced apoptosis in ARPE-19 cells through the transcriptional regulation of apoptotic elements and downregulation of the p38 MAPK pathway

PURPOSE

Toxoplasmosis, which is caused by the protozoan parasite Toxoplasma gondii, can lead to severe visual impairment. T. gondii inhibits or delays programmed cell death caused by various apoptotic triggers; however, the mechanisms involved in the T. gondii-induced suppression of apoptosis in retinal cells have not been analysed in detail.

METHODS

We investigated the role of T. gondii infection in H(2)O(2) -induced apoptosis in human retinal pigment epithelial cells (ARPE-19) by monitoring the activities of apoptosis-regulating molecules and mitogen-activated protein kinases (MAPKs), including p38 MAPK. We also examined the gene downstream from p38 MAPK.

RESULTS

T. gondii infection significantly inhibited the cellular toxicity of H(2)O(2) (500 μm) and increased cell viability in a multiplicity of infection (MOI)-dependent manner by reducing DNA fragmentation and reactive oxygen species (ROS) generation in ARPE-19 cells. Western blot analysis also showed that T. gondii infection prevented the host cell expression of pro-apoptotic factors, such as Bad and Bax, and the activation of caspase-3. Infection with T. gondii increased the expression of the anti-apoptotic factor Bcl-2 in ARPE-19 cells under oxidative stress. In accordance with these findings, Toxoplasma infection was protective enough to suppress the phosphorylation of p38 MAPK following H(2)O(2) treatment. Exposure to H(2)O(2) increased the expression of heme oxygenase-1 (HO-1) in ARPE-19 cells, and its expression was significantly inhibited in H(2)O(2) -treated infected cells.

CONCLUSION

The protective function of T. gondii infection against ROS-induced apoptosis results from changes in the expression of apoptotic molecules and the downregulation of stress-induced intracellular signalling.

Toxoplasma gondii down modulates cadherin expression in skeletal muscle cells inhibiting myogenesis

Background

Toxoplasma gondii belongs to a large and diverse group of obligate intracellular parasitic protozoa. Primary culture of mice skeletal muscle cells (SkMC) was employed as a model for experimental toxoplasmosis studies. The myogenesis of SkMC was reproduced in vitro and the ability of T. gondii tachyzoite forms to infect myoblasts and myotubes and its influence on SkMC myogenesis were analyzed.

Results

In this study we show that, after 24 h of interaction, myoblasts (61%) were more infected with T. gondii than myotubes (38%) and inhibition of myogenesis was about 75%. The role of adhesion molecules such as cadherin in this event was investigated. First, we demonstrate that cadherin localization was restricted to the contact areas between myocytes/myocytes and myocytes/myotubes during the myogenesis process. Immunofluorescence and immunoblotting analysis of parasite-host cell interaction showed a 54% reduction in cadherin expression at 24 h of infection. Concomitantly, a reduction in M-cadherin mRNA levels was observed after 3 and 24 h of T. gondii-host cell interaction.

Conclusions

These data suggest that T. gondii is able to down regulate M-cadherin expression, leading to molecular modifications in the host cell surface that interfere with membrane fusion and consequently affect the myogenesis process.

CXCL10 is required to maintain T-cell populations and to control parasite replication during chronic ocular toxoplasmosis

PURPOSE

Toxoplasma gondii is a major cause of ocular disease, which can lead to permanent vision loss in humans. T cells are critically involved in parasite control, but little is known about the molecules that promote T-cell trafficking and migration in the retina. Thus, the aim of this study was to image and dissect the T-cell response during chronic toxoplasmic retinochoroiditis.

METHODS

C57BL/6 mice were infected with the Me49 strain of T. gondii, and T cells that infiltrated the eye were analyzed by flow cytometry and imaged using multiphoton microscopy. IFN-γ, CXCL9, CXCL10, and CXCR3 mRNA levels were measured by real-time PCR. To investigate the role of CXCL10, mice were treated with anti-CXCL10 antibodies, and histopathology and immunohistochemistry were performed to monitor changes in pathology, cellular infiltration, and parasite burden in the eye.

RESULTS

Infection with T. gondii leads to the infiltration of highly activated motile T cells into the eye. These cells express CXCR3 and are capable of producing IFN-γ and TNF-α, and CD8+ T cells express granzyme B. The expression of CXCL9 and CXCL10 in the retina was significantly upregulated during chronic infection. Treatment of chronically infected mice with anti-CXCL10 antibodies led to decreases in the numbers of CD3+, CD4+, and CD8+ T cells and the amount of IFN-γ mRNA expression in the retina and an increase in replicating parasites and ocular pathology.

CONCLUSIONS

The maintenance of the T-cell response and the control of T. gondii in the eye during chronic infection is dependent on CXCL10.

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.

Toxoplasma gondii: epidemiology, feline clinical aspects, and prevention

Toxoplasma gondii is a parasite of birds and mammals. Cats are the only definitive host and thus the only source of infective oocysts, but other mammals and birds can develop tissue cysts. Although feline infections are typically asymptomatic, infection during human pregnancy can cause severe disease in the fetus. Cat owners can reduce their pets' exposure risk by keeping all cats indoors and not feeding them raw meat. Humans usually become infected through ingestion of oocyst-contaminated soil and water, tissue cysts in undercooked meat, or congenitally. Because of their fastidious nature, the passing of non-infective oocysts, and the short duration of oocyst shedding, direct contact with cats is not thought to be a primary risk for human infection.

DNA topoisomerases in apicomplexan parasites: promising targets for drug discovery

The phylum Apicomplexa includes a large group of protozoan parasites responsible for a wide range of animal and human diseases. Destructive pathogens, such as Plasmodium falciparum and Plasmodium vivax, causative agents of human malaria, Cryptosporidium parvum, responsible of childhood diarrhoea, and Toxoplasma gondii, responsible for miscarriages and abortions in humans, are frequently associated with HIV immunosuppression in AIDS patients. The lack of effective vaccines, along with years of increasing pressure to eradicate outbreaks with the use of drugs, has favoured the formation of multi-drug resistant strains in endemic areas. Almost all apicomplexan of medical interest contain two endosymbiotic organelles that contain their own mitochondrial and apicoplast DNA. Apicoplast is an attractive target for drug testing because in addition to harbouring singular metabolic pathways absent in the host, it also has its own transcription and translation machinery of bacterial origin. Accordingly, apicomplexan protozoa contain an interesting mixture of enzymes to unwind DNA from eukaryotic and prokaryotic origins. On the one hand, the main mechanism of DNA unwinding includes the scission of one-type I-or both DNA strands-type II eukaryotic topoisomerases, establishing transient covalent bonds with the scissile end. These enzymes are targeted by camptothecin and etoposide, respectively, two natural drugs whose semisynthetic derivatives are currently used in cancer chemotherapy. On the other hand, DNA gyrase is a bacterial-borne type II DNA topoisomerase that operates within the apicoplast and is effectively targeted by bacterial antibiotics like fluoroquinolones and aminocoumarins. The present review is an update on the new findings concerning topoisomerases in apicomplexan parasites and the role of these enzymes as targets for therapeutic agents.