Treating ocular toxoplasmosis: current evidence

New advances in immune mechanism and treatment during ocular toxoplasmosis

Ocular toxoplasmosis (OT) is an intraocular infection caused by the parasite Toxoplasma gondii. OT is manifested as retinal choroiditis and is the most common infectious cause of posterior uveitis. Invasion of the retina by T. gondii leads to disruption of the blood-ocular barrier and promotes the migration of immune cells to the ocular tissues. Cytokines such as IFN-γ and IL-1β are effective for controlling parasite growth, but excessive inflammatory responses can cause damage to the host. In this review, we will discuss in detail the latest advances in the immunopathology and treatment of OT.

Immune system roles in pathogenesis, prognosis, control, and treatment of Toxoplasma gondii infection

Toxoplasma gondii is the protozoan causative agent of toxoplasmosis in humans and warm-blooded animals. Recent studies have illustrated that the immune system plays a pivotal role in the pathogenesis of toxoplasmosis by triggering immune cytokines like IL-12, TNF-α, and IFN-γ and immune cells like DCs, Th1, and Th17. On the other hand, some immune components can serve as prognosis markers of toxoplasmosis. In healthy people, the disease is often asymptomatic, but immunocompromised people and newborns may suffer severe symptoms and complications. Therefore, the immune prognostic markers may provide tools to measure the disease progress and help patients to avoid further complications. Immunotherapies using monoclonal antibody, cytokines, immune cells, exosomes, novel vaccines, and anti-inflammatory molecules open new horizon for toxoplasmosis treatment. In this review article, we discussed the immunopathogenesis, prognosis, and immunotherapy of Toxoplasma gondii infection.

Ocular toxoplasmosis: a review of the current diagnostic and therapeutic approaches

PURPOSE

This review aims to summarize the current knowledge concerning the clinical features, diagnostic work-up and therapeutic approach of ocular toxoplasmosis focusing mainly on the postnatally acquired form of the disease.

METHODS

A meticulous literature search was performed in the PubMed database. A supplementary search was made in Google Scholar to complete the collected items.

RESULTS

Ocular toxoplasmosis is one of the most frequent infectious etiologies of posterior uveitis. It typically presents with retinochoroiditis. Setting an accurate diagnosis depends to a considerable degree on detecting characteristic clinical characteristics. In addition to the evaluation of clinical features, the diagnosis of toxoplasmosis relies at a large degree on serologic testing. The detection of the parasite DNA in the aqueous or vitreous humor can provide evidence for a definitive diagnosis. The current mainstay for the treatment, if necessary, is the use of oral antibiotic with systemic corticosteroids. Recent evidence suggests other therapeutic approaches, such as intravitreal antibiotics can be used.

CONCLUSION

Recent developments in the diagnostic and therapeutic approach have contributed to preventing or limiting vision loss of patients suffering from ocular toxoplasmosis. Further studies are required to provide a better understanding of epidemiology, pathogenesis, diagnosis, and treatment with a significant impact on the management of this challenging clinical entity.

Ocular toxoplasmosis: adverse reactions to treatment in a Brazilian cohort

Background

The purpose of this study was to estimate the frequency and describe the adverse drug reactions (ADRs) associated with the classic treatment of ocular toxoplasmosis (OT), namely sulfadiazine, pyrimethamine, corticosteroids and folinic acid.

Methods

We performed a descriptive study of a prospective cohort of patients with OT treated with the classic therapy. Data were collected during medical consultations and treatment.

Results

Of the 147 patients studied, 85% developed one or more ADR. Women presented more ADRs than men (95% vs 77%). Of the total reactions (n=394), 82% were mild, but we found one life-threatening event (Stevens-Johnson syndrome). The most frequent types (71%) of ADRs were gastrointestinal, skin and neurological or psychiatric. The majority of ADRs (90.3%) occurred before the second week of treatment. A third of the patients were treated for the ADR and 10% dropped out of OT treatment. Most (70%) of the ADRs were characterized as being probably caused by the drugs and may be associated with prednisone, sulfadiazine and sulfadiazine/prednisone. Six percent of ADRs were not previously described, such as taste alteration, constipation/bloating, dyspnoea, sweating and somnolence.

Conclusions

Our results suggest a high rate of ADRs to OT classic treatment, which requires careful follow-up in order to identify and treat ADRs early.

Vaccination challenges and strategies against long-lived Toxoplasma gondii

Since the discovery of Toxoplasma gondii in 1908, it is estimated that one-third of the global population has been exposed to this ubiquitous intracellular protozoan. The complex life cycle of T. gondii has enabled itself to overcome stress and transmit easily within a broad host range thus achieving a high seroprevalence worldwide. To date, toxoplasmosis remains one of the most prevalent HIV-associated opportunistic central nervous system infections. This review presents a comprehensive overview of different vaccination approaches ranging from traditional inactivated whole-T. gondii vaccines to the popular DNA vaccines. Extensive discussions are made to highlight the challenges in constructing these vaccines, selecting adjuvants as well as delivery methods, immunisation approaches and developing study models. Herein we also deliberate over the latest and promising enhancement strategies that can address the limitations in developing an effective T. gondii prophylactic vaccine.

Evaluation of immune responses induced by rhoptry protein 5 and rhoptry protein 7 DNA vaccines against Toxoplasma gondii

Infection with the protozoan parasite Toxoplasma gondii is widespread, and the organism can cause congenital infections in humans. The horizontal transmission of Toxoplasma is even more common than congenital. An effective vaccine strategy brings the prospect of improving Toxoplasma disease control. Rhoptry protein 5 (ROP5) and ROP7 are potential stimulators of humoral and cellular immune responses. In this study, we constructed a multi-antigenic DNA vaccine expressing ROP5 and ROP7 of T. gondii and compared the protective efficacy to single-gene vaccines and control groups. BALB/c mice were immunized intramuscularly three times. The levels of IgG antibodies and cytokines in mice immunized with the multi-antigenic DNA vaccine (pROP5/ROP7) were significantly higher than those in the control mice. Mice vaccinated with pROP5/ROP7 showed a longer survival time (16 days) than single-gene-immunized mice (11 and 12 days, respectively) or control mice (8 days) after a challenge with 1 × 10(4) tachyzoites of RH strain of T. gondii. Furthermore, after intragastric infection with 20 cysts of PRU strain of T. gondii, the number of brain cysts in mice immunized with pROP5/ROP7 was only 25% of the number in control mice. Our results showed that a DNA vaccine encoding ROP5 and ROP7 significantly enhanced protection against T. gondii challenge.

The Impact of Short-Term, Intensive Antifolate Treatment (with Pyrimethamine and Sulfadoxine) and Antibiotics Followed by Long-Term, Secondary Antifolate Prophylaxis on the Rate of Toxoplasmic Retinochoroiditis Recurrence

PURPOSE

To assess the impact of intensive antifolate treatment, followed by secondary antifolate prophylaxis (A-SP) on the recurrence rate of toxoplasmic retinochoroiditis (TRC). To investigate whether there are any other factors potentially predisposing for recurrence.

MATERIAL AND METHODS

A total of 637 medical records of TRC patients, who had been treated in the years 1994-2013 were reviewed. All patients were treated with pyrimethamine /sulfadoxine one 25mg/500mg tablet daily (P/S 25/500mg) for 21 days with a double loading dose for the first two days. From Day 2 the patients also received prednisone at a starting dose of 40mg and spiramycine 3 million IU three times daily, given for 10 days followed by azithromycin 500mg once daily for another 6 days. The analysis of the recurrence rate involved 352 patients who had completed 6-month secondary prophylaxis (P/S one 25 mg/500mg tablet twice a week).

RESULTS

When secondary antifolate prophylaxis (A-SP) was instituted immediately after the treatment for TRC, the probability of 3-year recurrence-free survival after the first course of A-SP was 90.9%. A recurrence was most likely approximately 3.5 years after the first treatment. A univariate Cox regression model demonstrated that a risk for recurrence was 2.82 times higher (p = 0.02) in patients with retinal scars. In the multivariate analysis, the risk for recurrence was 2.41 higher (p = 0.06). In patients with haemorrhagic lesions the risk for recurrence was lower, aRR = 0.17 (approaching borderline statistical significance p = 0.08).

CONCLUSIONS

With the institution of A-SP of immediately after the intensive treatment for TRC, i.e. when a reactivation was most likely, there was no recurrence during A-SP. Following A-SP the recurrence rates were low and recurrence-free periods tended to be longer. The treatment regimen employed had a beneficial effect on the recurrence interval as it reduced and delayed the highest probability of recurrence.

Host and Toxoplasma gondii genetic and non-genetic factors influencing the development of ocular toxoplasmosis: A systematic review

Toxoplasmosis is a cosmopolitan infection caused by the apicomplexan parasite Toxoplasma gondii. This infectious disease is widely distributed across the world where cats play an important role in its spread. The symptomatology caused by this parasite is diverse but the ocular affectation emerges as the most important clinical phenotype. Therefore, we conducted a systematic review of the current knowledge of ocular toxoplasmosis from the genetic diversity of the pathogen towards the treatment available for this infection. This review represents an update to the scientific community regarding the genetic diversity of the parasite, the genetic factors of the host, the molecular pathogenesis and its association with disease, the available diagnostic tools and the available treatment of patients undergoing ocular toxoplamosis. This review will be an update for the scientific community in order to encourage researchers to deploy cutting-edge investigation across this field.

Experimental Models of Ocular Infection with Toxoplasma Gondii

Ocular toxoplasmosis is a vision-threatening disease and the major cause of posterior uveitis worldwide. In spite of the continuing global burden of ocular toxoplasmosis, many critical aspects of disease including the therapeutic approach to ocular toxoplasmosis are still under debate. To assist in addressing many aspects of the disease, numerous experimental models of ocular toxoplasmosis have been established. In this article, we present an overview on in vitro, ex vivo, and in vivo models of ocular toxoplasmosis available to date. Experimental studies on ocular toxoplasmosis have recently focused on mice. However, the majority of murine models established so far are based on intraperitoneal and intraocular infection with Toxoplasma gondii. We therefore also present results obtained in an in vivo model using peroral infection of C57BL/6 and NMRI mice that reflects the natural route of infection and mimics the disease course in humans. While advances have been made in ex vivo model systems or larger animals to investigate specific aspects of ocular toxoplasmosis, laboratory mice continue to be the experimental model of choice for the investigation of ocular toxoplasmosis.

Time patterns of recurrences and factors predisposing for a higher risk of recurrence of ocular toxoplasmosis

PURPOSE

To ascertain time patterns of recurrences and factors predisposing for a higher risk of recurrence of ocular toxoplasmosis.

METHODS

Retrospective observational case series with follow-up examination. Database of 4,381 patients with uveitis was used. Data of 84 patients with ocular toxoplasmosis (sample group) could be included.

RESULTS

Two hundred and eighty active lesions in the first affected eye were detected. The mean number of recurrences per year was 0.29 (standard deviation, 0.24). Median recurrence-free survival time was 2.52 years (95% confidence interval, 2.03-3.02 years). Risk of recurrence was highest in the first year after the most recent episode (26%) implying a decrease with increasing recurrence-free interval. The risk of recurrence decreased with the duration of disease (P < 0.001). Treatment of the first active lesion influenced the risk of recurrence (P = 0.048). Furthermore, the risk of recurrence was influenced by patient age at the time of the first active lesion (P = 0.021) and the most recent episode (P = 0.002).

CONCLUSION

A secondary antibiotic prophylaxis could be discussed 1) during the first year after an active lesion has occurred, especially in case of the first active lesion of ocular toxoplasmosis, and 2) in older patients, especially if primarily infected with Toxoplasma gondii at an older age.

Risk of Recurrence of Preexisting Ocular Toxoplasmosis during Pregnancy

PURPOSE

Comparison between the risk of recurrence during pregnancy with nonpregnant periods in patients with ocular toxoplasmosis (OT).

METHODS

Records of 40 women were retrospectively reviewed. The women were subdivided into either a pregnant group or a control group formed by nonpregnant women during follow-up. Comparable cases from the literature were added. Mean number of recurrences per year was compared.

RESULTS

Eleven women with pregnancies could be included. Six cases from the literature were added (total n = 17). Mean number of recurrences per year during versus not during pregnancy was 0.16 (SD 0.39) versus 0.32 (SD 0.30; p = 0.088), respectively. In the control group (n = 29) the mean number of recurrences per year (0.31; SD 0.27) was significantly higher when compared to cases during pregnant periods (p = 0.002).

CONCLUSION

Adding to published series, the presented data do not provide evidence for a relevant impact of pregnancy on recurrence behavior in OT.

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.

Toxoplasma gondii: immune response and protective efficacy induced by ROP16/GRA7 multicomponent DNA vaccine with a genetic adjuvant B7-2

Toxoplasma gondii infection occurs commonly in humans and other warm-blooded animals. Its serious impact on public health and livestock sectors makes the development of an effective vaccine particularly important. In the current study, we constructed a multiantigenic DNA vaccine expressing ROP16 and GRA7 of T. gondii and evaluated the protective efficacy of these two fragments with or without a plasmid encoding murine costimulatory molecule B7-2. These recombinant eukaryotic expression plasmids were termed pROP16, pGRA7, pROP16-GRA7 and pB7-2, respectively. After intramuscular immunization in Kunming mice, we assessed the immune response using cytokine and antibody determinations, T lymphocyte subsets analysis, and the survival times of mice post acute T. gondii challenge. The results showed that mice immunized with the multiantigenic DNA vaccine pROP16-GRA7 gained higher levels of IgG titers and IgG2a subclass titers, production of IFN-γ, percentage of CD8+ T cells and median survival times against the acute infection of T. gondii compared with those of mice administered with pROP16 or pGRA7 and those in control groups. Moreover, the adjuvant pB7-2 formulated with DNA vaccine boosted these humoral and cellular (Th1, CD8+ T cell) immune responses. Therefore, it might be a promising genetic adjuvant to DNA vaccine against T. gondii for further investigation.

Ocular manifestations of systemic disease: toxoplasmosis

PURPOSE OF REVIEW

To provide an overview of ocular toxoplasmosis, the leading cause of infectious posterior uveitis, focusing on recent trends of disease epidemiology, pathogenesis, diagnosis, therapy and prevention.

RECENT FINDINGS

Novel aspects of epidemiology, including growing importance of water transmission are discussed. The historical controversy of congenital versus postnatally acquired toxoplasmosis is revisited. Recent insights into pathogenesis of ocular toxoplasmosis are also reviewed, tipping the delicate balance between parasite virulence and host immunity. Diagnosis of ocular toxoplasmosis is also discussed in the light of serological, molecular and imaging tools. Finally, a critical analysis of current and emerging therapies for ocular toxoplasmosis is made. Preventive aspects are also commented upon.

SUMMARY

Waterborne toxoplasmosis is increasingly recognized in outbreaks and in endemic areas. The importance of postnatally acquired toxoplasmosis is now well established, but should not lead to underestimation of congenital disease. Genetic determination of parasite virulence/individual susceptibility might correlate with disease outcomes. Serological, molecular and imaging tools may improve the diagnosis and follow-up of individuals with ocular toxoplasmosis. Despite emergence of alternative therapeutic regimens, including intravitreal antibiotics, classical therapy with sulfadiazine/pyrimethamine is still standard for toxoplasmic retinochoroiditis. Adequate prophylaxis is expected to have an effect in ocular burden of toxoplasmosis.

Toxoplasma gondii migration within and infection of human retina

Toxoplasmic retinochoroiditis is a common blinding retinal infection caused by the parasite, Toxoplasma gondii. Basic processes relating to establishment of infection in the human eye by T. gondii tachyzoites have not been investigated. To evaluate the ability of tachyzoites to navigate the human retina, we developed an ex vivo assay, in which a suspension containing 1.5 × 10(7) parasites replaced vitreous in a posterior eyecup. After 8 hours, the retina was formalin-fixed and paraffin-embedded, and sections were immunostained to identify tachyzoites. To determine the preference of tachyzoites for human retinal neuronal versus glial populations, we infected dissociated retinal cultures, subsequently characterized by neuron-specific enolase or glial fibrillary acidic protein expression, and retinal cell lines, with YFP-expressing tachyzoites. In migration assays, retinas contained 110-250 live tachyzoites; 64.5-95.2% (mean  =79.6%) were localized to the nerve fiber layer, but some were detected in the outer retina. Epifluorescence imaging of dissociated retinal cultures 24 hours after infection indicated preferential infection of glia. This observation was confirmed in growth assays, with significantly higher (p ≤ 0.005) numbers of tachyzoites measured in glial verus neuronal cell lines. Our translational studies indicate that, after entering retina, tachyzoites may navigate multiple tissue layers. Tachyzoites preferentially infect glial cells, which exist throughout the retina. These properties may contribute to the success of T. gondii as a human pathogen.

Therapy for ocular toxoplasmosis

PURPOSE

To review current evidence for the treatment of ocular toxoplasmosis (OT).

DESIGN

Narrative review and expert recommendations.

METHODS

Meta-analysis and selected original articles from the medical literature were reviewed critically. Expert recommendations were analyzed.

RESULTS

Numerous observational studies suggest a benefit of short-term antimicrobial therapy for toxoplasmic retinochoroiditis in immunocompetent patients, although its efficacy has not been proven in randomized clinical trials. A randomized clinical trial revealed that intermittent trimethoprim/sulfamethoxazole treatment could decrease the rate of recurrence in high-risk patients. Intravitreal injection of clindamycin and dexamethasone was an acceptable alternative to the classic treatment for OT in a randomized clinical trial.

CONCLUSIONS

Opinions about therapy differ and controversy remains about its type, efficacy, and length. Intravitreal therapy may be promising for OT. A recent description of the presence of parasitemia in patients with active and inactive ocular toxoplasmosis raises new questions that need to be explored.

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.

Parasitic infections and myositis

Infectious myositis may be caused by a wide variety of bacterial, fungal, viral, and parasitic agents. Parasitic myositis is most commonly a result of trichinosis, cystericercosis, or toxoplasmosis, but other parasites may be involved. A parasitic cause of myositis is suggested by history of residence or travel to endemic area and presence of eosinophilia. The diagnosis of parasitic myositis is suggested by the clinical picture and radiologic imaging, and the etiologic agent is confirmed by parasitologic, serologic, and molecular methods, together with histopathologic examination of tissue biopsies. Therapy is based on the clinical presentation and the underlying pathogen. Drug resistance should be put into consideration in different geographic areas, and it can be avoided through the proper use of anti-parasitic drugs.

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.

Annual burden of ocular toxoplasmosis in the US

Toxoplasmosis is the most common retinal infection in the United States, and it can severely impact vision. We used data from population-based studies, outbreaks, and the U.S. census to estimate the burden of Toxoplasma gondii infection and ocular toxoplasmosis. We estimate that 1,075,242 persons are infected with T. gondii, 21,505 persons have ocular lesions (both asymptomatic and symptomatic), and 4,839 (range = 2,150-7,527) persons develop symptomatic ocular toxoplasmosis each year in the United States. Toxoplasmosis contributes a significant burden to eye disease in the United States.