[Diagnosis and treatment of ocular toxoplasmosis : a survey of German-speaking ophthalmologists]

[Toxoplasma gondii-Current drugs and future vaccines against an underestimated protozoan infection]

Toxoplasma gondii is a unicellular organism of the Apicomplexa that occurs worldwide and is therefore a close relative of the malaria pathogen Plasmodium. As T. gondii infests every warm-blooded vertebrate species as an intermediate host and has a very high prevalence worldwide, toxoplasmosis is one of the most important international foodborne diseases. Potential vaccines (human as well as veterinary) play a crucial role in controlling this disease.

Treatment Strategy in Human Ocular Toxoplasmosis: Why Antibiotics Have Failed

Background: There is currently no clear evidence of the effectiveness of antibiotic therapy in acute ocular toxoplasmosis (OT), but its effect as a secondary prophylaxis is undisputed. The majority of uveitis specialists advocate treatment. This meta-analytic review aims to critically analyze determinants of treatment success and to update current treatment strategies for OT in order to explain this discrepancy. Methods: A systematic literature search was performed in NCBI/PubMed, Clinical Trials, Google Scholar and ScienceDirect to retrieve pro- and retrospective studies using the key terms “ocular toxoplasmosis” or “retinochoroiditis” and “immunocompetent” and “treatment” or “therapy” and “human.” Of these, larger case series and prospective clinical studies and cross references identified from meta-analyses were selected by a manual search, and primary and secondary outcome parameters were extracted. Results: Ten case series and clinical trials reported success parameters for treatment outcomes, and four additional for recurrence prophylaxis. Five treatment studies were randomized clinical trials, three comparative and two noncomparative case series. Though several outcome parameters were reported, five of them defined time to healing, four visual gain and one lesion size as primary and secondary outcome parameters, recurrence rate as a secondary outcome parameter was reported once. No conclusive evidence was found for an antibiotic treatment effect. Four prophylaxis studies addressed the prevention of recurrences after treatment. The primary outcome in all studies was the effect of treatment and prophylaxis on recurrences, and all four found a significant effect on the risk of and time to recurrences. Conclusions: Antibiotic treatment of OT aims at controlling parasite proliferation. The absence of an effect on visual acuity and time to healing is thus not surprising. The fact that time to and number of recurrences respond to recurrence of prophylaxis proves the antibiotic effect on parasite activity.

Current Practices in Ocular Toxoplasmosis: A Survey of Brazilian Uveitis Specialists

PURPOSE

To describe treatment practices for ocular toxoplasmosis among members of the Brazilian Uveitis Society.

METHODS

An online questionnaire sent to specialists, between October 2014 and March 2015.

RESULTS

Most respondents (67.9%) treat all active cases. Most specialists consider visual acuity <20/200 (88.2%), severe vitreous inflammation (94.1%), and ocular disease during acquired infection (88.2%) as absolute indications for treatment. Systemic steroids are associated with anti-toxoplasmic therapy in most cases by 50.9% of the respondents. For immunocompetent individuals, 57.4% of the respondents chose trimethoprim/sulfamethoxazole. Classical therapy (sulfadiazine/pyrimethamine) is preferred most for patients with central lesions (70.4%), immunosuppression (68.4%), acquired infection (70.4%), and atypical forms (74.1%). For patients with frequent relapses, 84.9% of the respondents preferred antibiotic prophylaxis.

CONCLUSIONS

Treatment patterns of ocular toxoplasmosis are not uniform among Brazilian specialists. Most specialists treat all cases of active retinochoroiditis. Typical cases are more frequently treated with trimethoprim/sulfamethoxazole. However, classical therapy is the regimen of choice when lesions are considered more severe.

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.

Animals are key to human toxoplasmosis

Toxoplasma gondii is an extremely sucessfull protozoal parasite which infects almost all mamalian species including humans. Approximately 30% of the human population worldwide is chronically infected with T. gondii. In general, human infection is asymptomatic but the parasite may induce severe disease in fetuses and immunocompromised patients. In addition, T. gondii may cause sight-threatening posterior uveitis in immunocompetent patients. Apart from few exceptions, humans acquire T. gondii from animals. Both, the oral uptake of T. gondii oocysts released by specific hosts, i.e. felidae, and of cysts persisting in muscle cells of animals result in human toxoplasmosis. In the present review, we discuss recent new data on the cell biology of T. gondii and parasite diversity in animals. In addition, we focus on the impact of these various parasite strains and their different virulence on the clinical outcome of human congenital toxoplasmosis and T. gondii uveitis.

An ophthalmologist survey-based study of the atypical presentations and current treatment practices of ocular toxoplasmosis in India

The last two decades have seen a paradigm shift in the understanding of ocular toxoplasmosis. Post-natally acquired infection with its atypical presentations, has emerged as a common form of the disease. We conducted a questionnaire-based survey to investigate the characteristics of atypical presentations and current treatment practices of ocular toxoplasmosis, in India. A written questionnaire was distributed to ophthalmologists at two major uveitis meetings, held in Hyderabad, India in January, 2009. It evaluated characteristics of atypical presentations of ocular toxoplasmosis and specific treatment-related issues in India. Of 37 respondents who completed the questionnaire, 28 (75.6%) found atypical presentations in less than one-fourth of ocular toxoplasmosis patients. Atypical presentations were mostly seen as primary retinitis lesion, and in healthy immuno-competent individuals. Most ophthalmologists (n = 28, 75.6%) thought viral retinitis to be the most common differential diagnosis for atypical ocular toxoplasmosis and relied on serological tests (n = 19, 51.3%) for the diagnosis. Twenty-three (62.1%) respondents treated all patients with active lesions. A diverse range of treatment regimens were used, trimethoprim-sulphamethoxazole combination being most common (n = 12, 32.4%). Corticosteroids were included in all regimens. Atypical presentations of ocular toxoplasmosis were identified by all ophthalmologists, participating in the survey, though not commonly by most. Treatment practices were diverse, reflecting the lack of consensus on this issue.