Toxoplasma gondii and ocular toxoplasmosis: pathogenesis

Vitreoretinal interface anomalies in patients with a history of toxoplasmosis retinochoroiditis

PURPOSE

To evaluate vitreoretinal interface anomalies over time in patients diagnosed with toxoplasmosis retinochoroiditis (TRC) and progression of the chronic disease.

STUDY DESIGN

Retrospective clinical study.

METHODS

The clinical records of 36 patients with TRC were studied retrospectively. All patients underwent standard ophthalmological examinations and optical coherence tomography (optical coherence tomography: OCT). Vitreoretinal interface changes and retinal layers in the macula and lesion area were evaluated.

RESULTS

The fovea was involved in 9 (25%) patients. OCT of the scar region showed retinal layer thinning and disorganization in all cases. Complete posterior vitreous detachment (PVD) was detected in 9 (25%) cases, incomplete PVD in 22 (61%) cases and no PVD in 5 (13.8%) cases. In 23 (63%) of the 36 patients with inactive TRC lesions, an epiretinal membrane (ERM) was detected by follow-up OCT, i.e., in 14 (60%) patients with incomplete PVD, 8 (34.7%) with complete PVD, and 1 (4%) with no PVD. Vitreoschisis was found in 5 of 22 patients with incomplete PVD; an ERM developed in 4 of these 5 patients. No ERM developed only in the macula, i.e., independent of the TRC scar region.

CONCLUSIONS

Vitreoretinal interface anomalies are common in patients diagnosed with TRC, including those with incomplete PVD. We observed no progression of vitreoretinal interface anomalies during the follow-up of patients diagnosed with TRC.

Posterior segment findings by spectral-domain optical coherence tomography and clinical associations in active toxoplasmic retinochoroiditis

Toxoplasmic retinochoroiditis is a common, potentially blinding parasitic infection. We sought to define the spectrum and frequency of signs of active toxoplasmic retinochoroiditis by spectral domain optical coherence tomography (SD-OCT), and to identify clinical associations. Ninety eyes of 90 individuals presenting consecutively to a tertiary referral uveitis service with active toxoplasmic retinochoroiditis and gradable SD-OCT scans were evaluated prospectively. SD-OCT features were collated, and associations with lesion location, primary versus recurrent episode, serological status, human immunodeficiency virus infection and best-corrected Snellen visual acuity were explored. Active toxoplasmic retinochoroiditis presented with thickened (65%) and hyperreflective (61%) retina, choroidal thickening (55%) and hyporeflectivity (61%), hyperreflective vitreous dots (80%) and deposits (36%), and posterior hyaloid thickening (35%) on SD-OCT. Most signs occurred with similar frequency across clinical groups. Retinal hyporeflectivity (17%) was significantly associated with a visual acuity of 20/200 or worse at resolution. Our observations demonstrate that active toxoplasmic retinochoroiditis has diverse SD-OCT signs and that none are universally present. Retinal hyporeflectivity—suggesting liquefactive necrosis—predicts poor visual outcome.

Expanded Spectrum of Optical Coherence Tomography Findings in Patients with Ocular Toxoplasmosis

Purpose: To describe the optical coherence tomography (OCT) findings of toxoplasmic retinochoroiditis at different stages of activity.Methods: Observational case series.Results: A total of 32 eyes of 31 patients were included; 43 sets of OCT were reviewed. A total of 14 lesions were classified as active, 13 as partially active, and 16 as inactive. All active lesions demonstrated increased retinal thickness and reflectivity with blurring of details of retinal layers. Choroidal granuloma was detected in eight (61.5%) and serous retinal detachment in nine (64%). In partially active lesions, sustained thickening and/or attachment of posterior hyaloid face with fine epiretinal membrane was the hallmark. Scarified lesions showed decreased retinal and choroidal thickness starting from the periphery. Characteristic signs for decreased activity of a lesion seen in majority of both partially active and inactive lesions were RPE changes and retina-RPE approximation. We called this unique feature 'hourglass configuration'.Conclusion: Features in OCT are helpful to specify and monitor the activity of toxoplasmic retinochoroiditis.

Optical coherence tomography findings in toxoplasma retinochoroiditis

Purpose:

This study aimed to evaluate the optic coherence tomography (OCT) findings in patients with toxoplasmic retinochoroiditis (TRC).

Methods:

A total of 12 eyes of 12 patients with active TRC were included in the study. At baseline, at the first-month follow-up, at the sixth-month follow-up and at the 1-year follow-up, the TRC lesion OCT and macula OCT were evaluated.

Results:

Hyperreflectivity of the inner retinal layers and an increase in retinal thickness were observed on the OCT examinations of all the patients with an active TRC lesion. The retinal thickness decreased and the reflectivity of retinal layers was disorganized in the OCT images obtained in the follow-up period. Partial posterior hyaloid detachment (PHD) and no PHD were detected in 11 cases and 1 case, respectively. Epiretinal membrane (ERM) had developed in the adjacent region of the scar in 7 patients. With the regression of the lesion, the disruption of the ellipsoid zone (EZ), retinal pigment epithelium (RPE) and external limiting membrane (ELM) improved in the adjacent areas. In all the eyes, ERM and the PHD configuration did progress during the follow-up period. Vitreoschisis was found in 4 of the 11 patients with partial PHD. It was observed that ERM developed in all the patients with vitreoschisis.

Conclusion:

ERM and partial PHD were common in the TRC patients, and there was no progression during the follow-up period. Regeneration of the EZ, RPE and ELM was observed in the follow-up period.

Implications of TORCH Diseases in Retinal Development-Special Focus on Congenital Toxoplasmosis

There are certain critical periods during pregnancy when the fetus is at high risk for exposure to teratogens. Some microorganisms, including Toxoplasma gondii, are known to exhibit teratogenic effects, interfering with fetal development and causing irreversible disturbances. T. gondii is an obligate intracellular parasite and the etiological agent of Toxoplasmosis, a zoonosis that affects one third of the world's population. Although congenital infection can cause severe fetal damage, the injury extension depends on the gestational period of infection, among other factors, like parasite genotype and host immunity. This parasite invades the Central Nervous System (CNS), forming tissue cysts, and can interfere with neurodevelopment, leading to frequent neurological abnormalities associated with T. gondii infection. Therefore, T. gondii is included in the TORCH complex of infectious diseases that may lead to neurological malformations (Toxoplasmosis, Others, Rubella, Cytomegalovirus, and Herpes). The retina is part of CNS, as it is derived from the diencephalon. Except for astrocytes and microglia, retinal cells originate from multipotent neural progenitors. After cell cycle exit, cells migrate to specific layers, undergo morphological and neurochemical differentiation, form synapses and establish their circuits. The retina is organized in nuclear layers intercalated by plexus, responsible for translating and preprocessing light stimuli and for sending this information to the brain visual nuclei for image perception. Ocular toxoplasmosis (OT) is a very debilitating condition and may present high severity in areas in which virulent strains are found. However, little is known about the effect of congenital infection on the biology of retinal progenitors/ immature cells and how this infection may affect the development of this tissue. In this context, this study reviews the effects that congenital infections may cause to the developing retina and the cellular and molecular aspects of these diseases, with special focus on congenital OT.

New findings useful for clinical practice using swept-source optical coherence tomography angiography in the follow-up of active ocular toxoplasmosis

Background

Ocular toxoplasmosis is one of the most common causes of intraocular inflammation and posterior uveitis in immunocompetent patients. This paper aims to investigate swept-source optical coherence tomography angiography (SS-OCTA) findings in eyes with active toxoplasmic retinochoroiditis.

Methods

This case series was conducted from November 2017 through October 2019 in two Brazilian centers. 15 eyes of 15 patients with active toxoplasmic retinochoroiditis were included, and were imaged at baseline and after at least 4 weeks of follow-up. All patients underwent ophthalmic examinations and multimodal imaging including SS-OCT and SS-OCTA before and after treatment of ocular toxoplasmosis. The differential diagnoses included toxoplasmosis, syphilis, and human immunodeficiency virus, which were eliminated through serologic and clinical evaluations.

Results

All 15 patients presented with positive anti-Toxoplasma gondii immunoglobulin G titers and three also presented with positive anti-T. gondii immunoglobulin M titers. The mean age at examination was 32.4 years ± 12.7 years (range 15–59 years). Sixty percent of the patients were female. In all eyes, the inner retinal layers were abnormally hyperreflective with full-thickness disorganization of the retinal reflective layers at the site of the active toxoplasmic retinochoroiditis. At baseline, 80% of eyes had focal choroidal thickening beneath the retinitis area, and all eyes had a choroidal hyporeflective signal. Before treatment, SS-OCTA showed no OCTA decorrelation signal next to the lesion site in all eyes, and flow signal improvement was noticed after treatment. Three eyes presented with intraretinal vascular abnormalities during follow-up. SS-OCTA showed retinal neovascularization in one patient and a presumed subclinical choroidal neovascular membrane in another patient.

Conclusions

SS-OCT and SS-OCTA are useful for assessing unexpected structural and vascular retinal and choroidal changes in active and post-treatment toxoplasmic retinochoroiditis and these findings are useful for clinical practice.

Long-term Results of Trimethoprim-Sulfamethoxazole Versus Placebo to Reduce the Risk of Recurrent Toxoplasma gondii Retinochoroiditis

PURPOSE

To compare the effects of 1 year of treatment with trimethoprim-sulfamethoxazole (TMP-SMZ) vs placebo in reducing the risk of recurrence of toxoplasmic retinochoroiditis during a 6-year follow-up period.

DESIGN

Randomized, double-masked clinical trial.

METHODS

This cohort included 141 subjects recruited in Campinas, Brazil. The inclusion criterion was unilateral active recurrent toxoplasmic retinochoroiditis. All subjects were treated with 1 dose of TMP-SMZ (160 mg/800 mg) twice daily for 45 days, and all lesions healed after this treatment. After this initial treatment, subjects were randomly assigned to group 1 (1 TMP-SMZ dose every other day for 311 days) or group 2 (1 identical placebo tablet containing starch with no active ingredients every other day for 311 days). Between the second and sixth years of follow-up appointments, none of the subjects received treatment unless a new recurrence episode had occurred. The primary outcomes were recurrent toxoplasmic retinochoroiditis within the first year of follow-up and recurrent toxoplasmic retinochoroiditis in the 6 years of follow-up.

RESULTS

The cumulative probability of recurrence 1, 2, 3, 4, 5, and 6 years after the initial infection was, respectively, 13.0% (9/69), 17.4% (12/69), 20.3% (14/69), 23.2% (16/69), 26.1% (18/69), and 27.5% (19/69) in the placebo group and 0%, 0%, 0%, 0%, 0%, and 1.4% (1/72) in the TMP-SMZ group (P < .001; log-rank test). There were 3 cases (3/69; 4.3%) of multiple recurrences in the same individual in the placebo group. No treatment-limiting toxicity or side effects were observed in either group. New recurrences were more frequent among female subjects.

CONCLUSIONS

TMP-SMZ may be used safely for prophylaxis of recurrent toxoplasmic retinochoroiditis and may provide long-term benefits.

Ocular Toxoplasmosis Presenting as Subretinal Macrocyst

Purpose:

To report a case of unilateral retinal detachment with a large subretinal macrocyst, representing an atypical presentation of ocular toxoplasmosis.

Case Report:

A healthy 30-year-old woman presented with a two month history of progressive visual loss in her right eye. Funduscopy revealed vitreous condensations, total retinal detachment with a large subretinal orange-red cystic mass and multiple retinal breaks sealed with surrounding retinal scars. B-scan echography showed a large subretinal cyst with non-homogenous tissue echogenicity. Pars plana deep vitrectomy and complete cyst removal were performed. Histopathologic examination of the excised cyst revealed intraretinal toxoplasma cysts containing bradyzoites. Analysis of intraocular fluids by polymerase chain reaction (PCR) and serologic tests also supported the diagnosis. After six months, the retina was completely attached with no signs of inflammation.

Conclusion:

Toxoplasma retinochoroiditis should be considered in the differential diagnoses of retinal detachment with subretinal cyst.

Trimethoprim-Sulfamethoxazole Versus Placebo in Reducing the Risk of Toxoplasmic Retinochoroiditis Recurrences: A Three-Year Follow-up

PURPOSE

To compare the effects of 1 year of treatment with trimethoprim/sulfamethoxazole (TMP-SMZ) vs a placebo in reducing the risk of toxoplasmic retinochoroiditis recurrences during a 3-year follow-up period.

DESIGN

Randomized, double-masked clinical trial.

METHODS

This cohort included 141 volunteers recruited in Campinas, Brazil. Inclusion criterion was unilateral active recurrent toxoplasmic retinochoroiditis. All volunteers were treated with 1 tablet of TMP-SMZ (160 mg/800 mg) twice daily for 45 days, and all lesions healed after this treatment. After this initial treatment, the volunteers were randomly assigned to Group 1 (1 TMP-SMZ tablet every 2 days for 311 days) or Group 2 (1 identical placebo tablet containing starch with no active ingredients every 2 days for 311 days). At the second- and third-year follow-up appointments, none of the volunteers received treatment unless a new recurrence episode had occurred. The primary outcomes were recurrent toxoplasmic retinochoroiditis within the first year of follow-up and recurrent toxoplasmic retinochoroiditis within the third year of follow-up.

RESULTS

The cumulative probability of recurrence at 1, 2, and 3 years of follow-up were, respectively, 13.0% (9/69), 17.4% (12/69), and 20.3% (14/69) in the placebo group and 0% (0/72) in the TMP-SMZ group (P < .001, log-rank test). There was no case of multiple recurrences in the same individual. No treatment-limiting toxicity or side effects were observed in either group. New recurrences were more frequent among female volunteers.

CONCLUSIONS

TMP-SMZ may be used safely for prophylaxis of recurrent toxoplasmic retinochoroiditis, with long-term benefits.

Toxoplasma gondii oral infection induces intestinal inflammation and retinochoroiditis in mice genetically selected for immune oral tolerance resistance

Toxoplasmosis is a worldwide disease with most of the infections originating through the oral route and generates various pathological manifestations, ranging from meningoencephalitis to retinochoroiditis and inflammatory bowel disease. Animal models for these pathologies are scarce and have limitations. We evaluated the outcome of Toxoplasma gondii oral infection with 50 or 100 cysts of the ME-49 strain in two lines of mice with extreme phenotypes of susceptibility (TS) or resistance (TR) to immune oral tolerance. Therefore, the aim of this study was to evaluate the behaviour of TS and TR mice, orally infected by T. gondii, and determine its value as a model for inflammatory diseases study. Mortality during the acute stage of the infection for TR was 50% for both dosages, while 10 and 40% of the TS died after infection with these respective dosages. In the chronic stage, the remaining TS succumbed while TR survived for 90 days. The TS displayed higher parasite load with lower intestinal inflammation and cellular proliferation, notwithstanding myocarditis, pneumonitis and meningoencephalitis. TR presented massive necrosis of villi and crypt, comparable to inflammatory bowel disease, with infiltration of lymphoid cells in the lamina propria of the intestines. Also, TR mice infected with 100 cysts presented intense cellular infiltrate within the photoreceptor layer of the eyes, changes in disposition and morphology of the retina cell layers and retinochoroiditis. During the infection, high levels of IL-6 were detected in the serum of TS mice and TR mice presented high amounts of IFN-γ and TNF-α. Both mice lineages developed different disease outcomes, but it is emphasized that TR and TS mice presented acute and chronic stages of the infection, demonstrating that the two lineages offer an attractive model for studying toxoplasmosis.

Risk of reactivation of toxoplasmic retinitis following intraocular procedures without the use of prophylactic therapy

BACKGROUND/AIMS

Toxoplasmic retinochoroiditis is the commonest known cause of posterior uveitis worldwide and reactivation is unpredictable. Based on results from one study, the authors proposed that antitoxoplasmic therapy should be initiated as prophylaxis for intraocular surgery in patients with toxoplasmic scars. The aim of this study is to analyse the risk of toxoplasmic retinochoroiditis reactivation following intraocular procedures.

METHODS

Retrospective analysis of the medical records of a total of 69 patients who underwent intraocular surgery and presented with toxoplasmic retinochoroiditis scars.

RESULTS

No patient received prophylactic antitoxoplasmic therapy. Reactivation following the surgical procedure occurred in four cases, with one at 3 months and the others respectively at 13, 14 and 17 months.

CONCLUSIONS

Our study shows that intraocular surgery did not result in a significant reactivation rate of toxoplasmic retinochoroiditis in the absence of preoperative prophylactic antitoxoplasmic therapy.

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.

Spectral optical coherence tomography findings in patients with ocular toxoplasmosis and active satellite lesions (MINAS Report 1)

PURPOSE

To characterize the active retinochoroiditis lesion observed in patients with the classic clinical presentation of ocular toxoplasmosis (OT) utilizing spectral optical coherence tomography (SOCT).

METHODS

Twenty-four patients with OT and satellite lesions underwent standardized ophthalmologic examination and multimodal fundus imaging. The SOCT findings observed at presentation were described.

RESULTS

The mean age of the fourteen (58.3%) women and ten (41.7%) men was 27.6 years. The mean LogMAR ETDRS best-corrected visual acuity was 0.58 (Snellen equivalent, 20/80(+1) ). On SOCT evaluation, the posterior hyaloid was diffusely thickened in 23 (95.8%) of 24 eyes, increased hyper-reflective signals in the vitreous were observed in 18 (75.0%), and vitreal spherical hyper-reflective depositions were observed in 12 (50.0%) eyes. In all patients, at the active OT lesion site, the inner retinal layers were abnormally hyper-reflective with full-thickness disorganization of the retinal reflective layers (smudge effect); associated choriocapillaris/choroidal optical shadowing was observed in 22 (91.7%) eyes. The retina was thickened in 22 (91.7%) eyes, the retinal pigment epithelium-Bruch membrane reflective complex was focally increased or contained focal splits in 16 (66.7%) eyes and the choroid appeared thickened in 17 (70.8%) eyes. Disorganization of the outer retinal highly reflective layers adjacent to the active OT lesion was observed in all eyes.

CONCLUSION

Full-thickness disorganization of the retinal reflective layers, generally associated with some degree of posterior optical shadowing, was observed in the active OT lesion in all patients. The posterior hyaloid was often thickened and, adjacent to the OT lesion, the outer retina was consistently altered.

Reactivation of ocular toxoplasmosis after pars plana vitrectomy

PURPOSE

To report a case with reactivation of toxoplasma choroiretinitis after pars plana vitrectomy.

PATIENTS AND METHODS

A 58-year-old female patient was diagnosed with secondary epiretinal membrane in her right eye. Bimanual 23-gauge pars plana vitrectomy and membrane peeling was performed. At first week postoperatively, visual acuity decreased; in slit-lamp examination, there were 3+ cells in the anterior chamber with keratic precipitate. Fundoscopic examination revealed reactivation of chorioretinitis adjacent to the previous scar.

RESULTS

The patient was diagnosed with reactivation of toxoplasma chorioretinitis and treated with oral trimethoprim-sulfamethoxazole, clindamycin and topical prednisolon acetate, and cyclopentolate drops for 5 weeks. Forty-eight hours after initiation of antibiotics, oral prednisone was added to the regimen and the dose was tapered to zero over the following 5 weeks. After 3 weeks of treatment, lesion was inactivated.

CONCLUSION

Ocular toxoplasmosis reactivation may develop after pars plana vitrectomy. After intraocular surgery, reactivation of ocular toxoplasmosis should be considered in the follow-up.

Prevalence, clinical characteristics, and causes of vision loss in patients with ocular toxoplasmosis

PURPOSE

To describe the prevalence, demographics, clinical features, and contributors to vision loss at presentation in a large cohort of patients with ocular toxoplasmosis seen at a tertiary referral center in northern California.

METHODS

A retrospective review of the charts of 233 patients with ocular toxoplasmosis examined over 24 years.

RESULTS

Ocular toxoplasmosis was diagnosed in 233 (8.4%) of 2761 patients with uveitis. The mean age at presentation was 27.2 years. Patients with ocular toxoplasmosis were more likely to be young (p<0.01), male (p<0.001), and Latino (p<0.001) as compared with patients in the entire uveitis cohort. At presentation, 159 patients (68.2%) had active disease, which was unilateral in all but one. Among the 160 eyes with active disease, 145 (90.6%) presented with a focal retinochoroiditis, 57.2% of which had an adjacent retinochoroidal scar. Atypical presentations occurred in 11 patients (6.9%). Of eyes with active disease, the main contributors to vision loss at presentation were intraocular inflammation (74.8%) and macular involvement (24.3%), whereas in eyes with inactive lesions the main contributors to vision loss were macular scar formation (67.9%) and amblyopia (11.3%). Younger age was the single significant predictor of macular involvement.

CONCLUSIONS

Ocular toxoplasmosis is a common cause of uveitis. Our patients were more likely than general uveitis patients to be young, male, and Latino, often having emigrated from Mexico or Central or South America. The most common contributors to decreased vision in eyes with active lesions were inflammation and macular involvement, whereas in eyes with inactive lesions they were macular scar formation and amblyopia.

Toxoplasma gondii and the blood-brain barrier

Infection with the protozoan parasite Toxoplasma gondii is characterized by asymptomatic latent infection in the central nervous system and skeletal muscle tissue in the majority of immunocompentent individuals. Life-threatening reactivation of the infection in immunocompromized patients originates from rupture of Toxoplasma cysts in the brain. While major progress has been made in our understanding of the immunopathogenesis of infection the mechanism(s) of neuroinvasion of the parasite remains poorly understood. The present review presents the current understanding of blood-brain barrier (patho)physiology and the interaction of Toxoplasma gondii with cells of the blood-brain barrier.

Review of the series "Disease of the year 2011: toxoplasmosis" pathophysiology of toxoplasmosis

Toxoplasma gondii is a major cause of chronic parasitic infection in the world. This protozoan can cause retino-choroiditis in newborns and in adults, both immunocompetent and immunodeficient. This disease tends to be recurrent and can lead to severe visual impairment. The authors review current knowledge on the role of parasite genetics in influencing susceptibility to ocular toxoplasmosis and on the immuno-pathogenesis of this disease.

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

BACKGROUND/PURPOSE

Ocular toxoplasmosis is the most frequent cause of posterior uveitis in Germany. The purpose of this survey was to evaluate current strategies in the management of ocular toxoplasmosis by uveitis specialists in Germany.

METHODS

An itemized questionnaire including clinical case reports with authentic photographs was distributed to physician members (n=40) of the German Uveitis Society. In addition, members were categorized regarding their clinical background, professional affiliation and experience with ocular toxoplasmosis.

RESULTS

The completed questionnaire was returned by 72% (29/40) of the members. According to the answers, the majority (70%) of responders base their diagnosis of ocular toxoplasmosis on clinical examination and serological findings. Although a positive IgM titre or increasing IgG titres support the diagnosis only in cases of recently acquired disease, these are reported to support the diagnosis by 58 and 41%, respectively. Invasive procedures such as aqueous humour analysis are performed by 59% of colleagues to establish the diagnosis in selected patients. A total of six antimicrobial agents were reported for treatment in different regimens for typical clinical conditions in patients with recurrent toxoplasmic retinochoroiditis. The combination of pyrimethamine and sulfadiazine is the most commonly used (48%), followed by clindamycin (38%).

CONCLUSIONS

Our survey indicates the lack of a "gold standard" for diagnosis and medical treatment in ocular toxoplasmosis. Further efforts have to be undertaken towards a better distribution of available information and to determine strategies for providing standards of continuously updated diagnostic and therapeutic recommendations for routine clinical practice.

Immunity and Toxoplasma retinochoroiditis

Toxoplasma infection accounts for up to 50% of all cases of posterior uveitis worldwide. In this review the control of Toxoplasma infection generally, and specific in the eye, by the immune system is discussed.

Forward genetic dissection of immunity to infection in the mouse

Forward genetics is an experimental approach in which gene mapping and positional cloning are used to elucidate the molecular mechanisms underlying phenotypic differences between two individuals for a given trait. This strategy has been highly successful for the study of inbred mouse strains that show differences in innate susceptibility to bacterial, parasitic, fungal, and viral infections. Over the past 20 years, these studies have led to the identification of a number of cell populations and critical biochemical pathways and proteins that are essential for the early detection of and response to invading pathogens. Strikingly, the macrophage is the point of convergence for many of these genetic studies. This has led to the identification of diverse pathways involved in extracellular and intracellular pathogen recognition, modification of the properties and content of phagosomes, transcriptional response, and signal transduction for activation of adaptive immune mechanisms. In models of viral infections, elegant genetic studies highlighted the pivotal role of natural killer cells in the detection and destruction of infected cells.

[Ocular toxoplasmosis]

Toxoplasmosis is a parasitic zoonosis which occurs worldwide and is an important cause of blindness. The infection is naturally acquired by the ingestion of oocysts excreted by infected cats or by ingestion of tissue cysts in undercooked or raw meat. Primary infection during pregnancy may result in a congenital infection. Toxoplasmic retinochoroiditis is the most common cause of posterior uveitis in immunocompetent patients. Depending on the patient's age, ocular symptoms vary presenting with reduced visual acuity, strabismus, and nystagmus in young children - in adults decreased vision and floaters are most frequently reported. Active toxoplasmic retinochoroiditis typically presents as grey-white retinal necrosis with choroiditis, vasculitis and vitritis. However, atypical presentations including neuroretinitis, papillitis, Fuchs-like anterior uveitis, scleritis and acute retinal necrosis have been described. The diagnosis is based on clinical findings and can be supported by the detection of antibodies and Toxoplasma gondii DNA. Toxoplasmosis therapy includes antimicrobial drugs and corticosteroids. There are several regimens with different drug combinations including, among others, pyrimethamine, sulfadiazine, clindamycin, and trimethoprim-sulfamethoxazol. The prognosis for ocular toxoplasmosis is favorable in immunocompetent individuals, as long as the central macula is not directly involved. The present article reviews the epidemiology, pathogenesis, clinical presentation and management of toxoplasmic retinochoroiditis.

[Recurrent toxoplasmic retinochoroiditis after clindamycin treatment]

PURPOSE

To evaluate the efficacy and safety of subconjunctival injections of clindamycin associated with oral corticotherapy in the treatment of toxoplasmic retinochoroiditis (TRC) and its effect on recurrence.

PATIENTS AND METHODS

This study investigated 21 patients (10 males and 11 females) who presented to an ophthalmological department from 1995 to 2000, aged 14-55 years (mean, 28 years), with unilateral TRC. They were treated with subconjunctival injections of clindamycin and systemic corticotherapy at a dose of 1 mg/kg/day. Clinical follow-up consisted of assessment of visual acuity and biomicroscopic fundus examination, completed by retinal angiography if necessary.

RESULTS

We observed clinical improvement in 68.75% of patients within 4 days and in all patients healing of the chorioretinal area within 1.6 months. During the follow-up period ranging from 6 to 52 months (mean, 22 months), there have been two recurrences (9%) over the first 18 months. Tolerance of the injections was good. Serious side effects were noted in two patients: one case of conjunctival necrosis and one case of corneal and conjunctival erosion.

CONCLUSION

In treating ocular toxoplasmosis, clindamycin appears to be a safe and effective substitute for the classic protocol (pyrimethamine-sulfadiazine, pyrimethamine-azithromycin), for which a 50% recurrence rate has been reported. It provides relatively good protection against recurrence and warrants testing in further controlled studies.

Vitreoretinal morphology in active ocular toxoplasmosis: a prospective study by optical coherence tomography

AIM

To investigate the third generation optical coherence tomography (OCT3) findings in patients with active ocular toxoplasmosis.

METHODS

A prospective observational case series, including 15 patients with active ocular toxoplasmosis in at least one eye evaluated at a single centre. Vitreoretinal morphological features at baseline and changes within a 24-week follow-up interval on OCT3 were evaluated.

RESULTS

The active ocular toxoplasmosis lesion was classified clinically as punctate (n = 6), focal (n = 6) or satellite (n = 3). Retinal layers were hyper-reflective at the active lesion site, and some degree of retinal pigment epithelium-choriocapillaris/choroidal optical shadowing was seen in all patients. In general, the retina was thinned at the active lesion site in eyes with punctate lesions and thickened in eyes with focal and satellite lesions. When detected by OCT3, the posterior hyaloid appeared thickened. While focally detached over punctate lesions, the posterior hyaloid was partially detached, but still attached to the lesion in focal and satellite lesions. Additional findings (not detected on clinical examination) include diffuse macular oedema (n = 6), vitreomacular traction (n = 3) and maculoschisis (n = 1). During follow-up, a decrease in retinal thickness and focal choriocapillaris/choroidal relative hyper-reflectivity were observed at the former lesion site, and posterior vitreous detachment progressed/occurred in all patients.

CONCLUSION

OCT3 enabled identification of morphological features underestimated on clinical examination in patients with ocular toxoplasmosis, which may expand the clinical spectrum of the disease. Further studies are needed to verify the relevance of OCT3 in assisting with the diagnosis and management of ocular toxoplasmosis.

Reactivation of Ocular Toxoplasmosis After LASIK

PURPOSE

To report a reactivation of ocular toxoplasmosis after LASIK.

METHODS

Case report of a 34-year-old man who underwent bilateral LASIK. The posterior segment examination revealed an old toxoplasmosis scar in the retinal periphery of the right eye.

RESULTS

Uncorrected visual acuity improved postoperatively, and the patient was satisfied. However, 52 days after the procedure, he complained of loss of visual acuity in his right eye. Examination revealed signs of anterior uveitis, vitreitis, and active chorioretinal lesion satellite of the old toxoplasmosis scar. The patient was treated with a multidrug regiment with resolution of the vitreous and lesion activity.

CONCLUSIONS

Toxoplasmosis reactivation may develop after LASIK.

Parasites and the eye

Systemic parasitic infections can result in intraocular inflammation. They are a major cause of blindness in many parts of the world. Infection usually results from bloodborne transmission of the organism to the eye or ocular adnexal structures. Diagnosis is often made from clinical patterns of disease in the eye, with laboratory investigations and imaging to support the diagnosis. Various local and systemic therapies are available, but may have limited success in preserving vision.

Atypical presentations of ocular toxoplasmosis

The diagnosis of ocular toxoplasmosis is based most often on the presence of characteristic clinical findings, which include focal retinochoroiditis, an adjacent or nearby retinochoroidal scar, and moderate to severe vitreous inflammation. However, a variety of less common, "atypical" presentations may be unfamiliar to clinicians, delaying both diagnosis and treatment. Patients who are immunocompromised or elderly may, for example, present with large, multiple and/or bilateral lesions. Other unusual manifestations include punctate outer retinal toxoplasmosis, retinal vasculitis, retinal vascular occlusions, rhegmatogenous and serous retinal detachments, a unilateral pigmentary retinopathy mimicking retinitis pigmentosa, neuroretinitis and other forms of optic neuropathy, and scleritis. Although in the past most cases of ocular toxoplasmosis were considered to result from reactivation of a congenital infection, it is now believed that postnatally acquired infection accounts for many cases of this disease. With appropriate use of antiparasitic therapy, the visual prognosis for patients with both typical and atypical forms of ocular toxoplasmosis may be good.

Reactivations of ocular toxoplasmosis after cataract extraction

PURPOSE

To determine the risk of reactivation of ocular toxoplasmosis following cataract extraction.

DESIGN

Retrospective case-control study.

PARTICIPANTS

Out of 154 patients with ocular toxoplasmosis, 14 patients (15 eyes) who had undergone a cataract extraction and 45 age- and sex- matched controls without cataract were selected.

INTERVENTION

A review of the medical records of 14 patients with ocular toxoplasmosis and cataract and 45 control patients with ocular toxoplasmosis but without cataract. The clinical records of the controls and patients were assessed for an identical 4-month period following the date of the cataract extraction in the index patients.

MAIN OUTCOME MEASURES

Development of a new active retinal lesion within 4 months after cataract surgery in patients and age -and sex matched-controls. The presence of risk factors such as sex, congenital or postnatal acquisition of ocular toxoplasmosis, age at first clinical manifestation of ocular toxoplasmosis, total number of attacks per affected eye, type of cataract, age at the time of cataract surgery and the intervals between surgery and first clinical manifestation of ocular toxoplasmosis and between surgery and the last recurrence of ocular toxoplasmosis, as well as the use of antiparasitic medication during surgery, type and complications of surgery and optimal visual acuity before and after cataract surgery.

RESULTS

Reactivations of ocular toxoplasmosis following cataract extraction occurred in 5/14 patients (5/15 eyes), which was higher than the incidence of recurrences in age -and sex-matched controls (p < 0.001). No additional risk factors for the development of recurrences of ocular toxoplasmosis after cataract surgery were found. Incidence of recurrences preceding surgery did not differ between patients and controls.

CONCLUSION

We identified an increased risk of reactivation of ocular toxoplasmosis following cataract extraction which implies that prophylactic treatment with antiparasitic drugs during and after the cataract surgery might be worthwhile for patients at risk of visual loss.

Immunoblotting can help the diagnosis of ocular toxoplasmosis

AIMS

To determine whether IgG immunoblotting can improve the diagnosis of ocular toxoplasmosis.

METHODS

Samples of serum were tested from patients with ocular lesions that could be caused by toxoplasmosis. All such samples from Scotland and Northern Ireland are usually referred to the Scottish Toxoplasma Reference Laboratory. From questionnaires filled out by the clinicians, two groups of sera were identified: ocular toxoplasmosis (active and quiescent), n = 54 (group 1); and eye disease as a result of other causes, n = 36 (group 2). Control groups were made up of sera from patients with no eye disease and a normal dye test result (< or = 125 IU/ml), n = 16 (group 3); and toxoplasma seronegative, cytomegalovirus (CMV) positive, and herpes simplex virus (HSV) positive sera (group 4), n = 18.

RESULTS

Immunoblots with an active pattern could be identified (IgG antibodies against at least four antigens with molecular weight of 6, 20, 22, 23, 25, and 36 kDa). Significantly more of this pattern was found in group 1 (33 of 54; 61.1%) compared with group 2 (nine of 36; 25%) or group 3 (six of 16; 37.5%). Within group 1, significantly more sera with an active pattern had dye test results > or = 65 IU/ml compared with those without. More sera from patients < 30 years of age were found with the active pattern in group 1 compared with group 2. No group 4 sera had active immunoblot patterns.

CONCLUSIONS

The immunoblot result adds more support to the diagnosis of ocular toxoplasmosis. In cases where the clinical diagnosis is difficult, immunoblots are particularly indicated; if negative, other causes of eye disease should be sought.

Toxoplasmosis in a patient with non-Hodgkin's lymphoma: the need for a good differential diagnosis

Toxoplasma gondii is an obligate intracellular parasite responsible for toxoplasmosis. Congenital and acquired forms of the disease have now been reported. In immunocompromised patients, the disease entity may resemble other diseases. Presented for discussion is an interesting case of acquired toxoplasmosis in an immunocompromised patient with several confounding factors necessitating a good differential diagnosis list. Also provided is a comprehensive review of toxoplasmosis diagnosis and management.

Early aqueous humor analysis in patients with human ocular toxoplasmosis

To evaluate the diagnostic sensitivity of a panel of laboratory tests for ocular toxoplasmosis performed at the time of presentation, paired samples of aqueous humor and serum were collected from 49 consecutive episodes of ocular toxoplasmosis with a clinical course of less than 3 weeks. Total immunoglobulin G (IgG) and Toxoplasma gondii-specific IgG, IgM, and IgA were quantified by enzyme-linked immunosorbent assay. The avidity of T. gondii-specific IgG was determined, and DNA extracted from aqueous humor was amplified for detection of a glycoprotein B gene sequence of T. gondii. The diagnosis was confirmed for 73% (36 of 49) of the patients; this rate rose to 79.5% if data from a later analysis of aqueous humor derived from five of the negative patients were included. The analysis of serum (detection of T. gondii-specific IgM and analysis of consecutive serum samples) alone did not contribute to the diagnosis. Calculation of local antibody production lacked diagnostic sensitivity when it was determined less than 3 weeks after the manifestation of clinical symptoms (28 of 49 patients [57%]), but this rose to 70% after an analysis of a second aqueous humor sample. The antibody avidity index attained diagnostic significance in only 8 of 43 instances (19%), and T. gondii DNA was amplified from no more than 6 of 39 (16%) aqueous humor samples. However, T. gondii-specific IgA was found within the aqueous humors of 11 of 43 patients (26%); measurement of the T. gondii-specific IgA level thus contributed substantially to the diagnostic sensitivity of the laboratory tests.

The effect of cytokines on the replication of T. gondii within rat retinal vascular endothelial cells

Toxoplasma gondii infection of the eye can result in a recurrent necrotising retinochoroiditis (TR) which may lead to a permanent loss of visual acuity. The mechanisms responsible for the control of TR within the retina are unknown. The aim of this study was to examine the effects of cytokines on the replication of T. gondii RH strain tachyzoites within rat retinal vascular endothelial (rRVE) cells. Pretreatment of rRVE with IFNgamma, TNF or IL-1beta resulted in a significant decrease in T. gondii replication from day 2 onwards. There was no significant difference in nitric oxide (NO) production by IFNgamma, TNF or IL-1beta treated rRVE as compared to controls at any time point. By comparison, the addition of L-tryptophan to IFNgamma treated cultures significantly restored T. gondii replication from 48 h post inoculation. Thus, IFNgamma, TNF and IL-1beta can significantly inhibit the replication of T. gondii within rRVE. However, this inhibition appears to be independent of NO production. L-tryptophan catabolism may have a role in IFNgamma mediated inhibition of T. gondii replication in rRVE cells.

Serologic evaluation of patients with primary and recurrent ocular toxoplasmosis for evidence of recent infection

PURPOSE

To identify the frequency of recently acquired vs chronic systemic Toxoplasma gondii infections in patients with ocular toxoplasmosis.

METHODS

Serum samples from 22 patients with primary ocular toxoplasmosis (not from scars) and 42 patients with recurrent ocular toxoplasmosis were tested for the presence of anti-T. gondii IgM, IgG, and IgA antibodies and compared with samples from 24 patients with other causes of uveitis. Intraocular production of anti-T. gondii IgG and IgA, and the presence of T. gondii DNA was determined in patient s and control subjects from whom ocular fluid was available.

RESULTS

Serologic evidence of recently acquired infection was found for 11 (50%) of 22 patients with primary ocular toxoplasmosis and for one (2%) of 42 with recurrent ocular toxoplasmosis. In the uveitis control group, anti-T. gondii IgM antibodies could be detected in two (8%) of 24 patients, but anti-T. gondii IgA antibodies were not detectable. Patients with primary ocular toxoplasmosis and serologic markers of recently acquired systemic infection were significantly older than those with chronic infection (P = .008). Intraocular production of anti-T. gondii IgG was more frequently noted in patients with recurrent than primary ocular toxoplasmosis (81% vs 41%; P < .001), but intraocular T. gondii DNA was more frequently found in patients with primary ocular toxoplasmosis than in those with recurrent ocular toxoplasmosis (37% vs 4%; P < .01).

CONCLUSIONS

Primary ocular toxoplasmosis can be seen in either recently acquired or chronic T. gondii infection. Patients with ocular disease and recently acquired infection were older and more likely to have T. gondii DNA in intraocular fluids.

Recurrent ocular disease in postnatally acquired toxoplasmosis

PURPOSE

Although recurrences are typical of congenital toxoplasmosis, the long-term ocular manifestations in postnatally acquired toxoplasmosis have never been systematically studied. We report on the ocular manifestations complicating the chronic phase of postnatally acquired toxoplasmosis.

METHODS

Review of the clinical data of 14 patients who presented with active ocular toxoplasmosis not associated with scars and who had serologic characteristics of recently acquired systemic toxoplasmosis.

RESULTS

Mean follow-up was 4.6 years. Recurrent ocular disease developed in eight (57%) of 14 cases. The number of patients with recurrences increased with the follow-up time: four (29%) of 14 during the first year of follow-up; eight (57%) of 14 during the second year; and eight of nine during the third follow-up year. No risk factors for the development of recurrences were identified. Satellite lesions developed in five of eight patients with recurrences, whereas lesions not adjacent to old scars, located in areas of previously unaffected retina, developed in three patients.

CONCLUSIONS

In postnatally acquired toxoplasmosis, frequent recurrences of ocular disease can be seen during the chronic phase of infection.