Ocular toxoplasmosis

Molecular Diagnostics for Ocular Infectious Diseases: LXXVIII Edward Jackson Memorial Lecture

PURPOSE

To review the use of molecular diagnostic techniques in the management of ocular infectious disease.

DESIGN

Retrospective review.

METHODS

A combination of literature review and personal recollections are used.

RESULTS

Although the broad term molecular diagnostics may encompass techniques to identify pathogens via protein or metabolomic signatures, this review concentrates on detection of pathogen nucleic acid as an indicator of infection. The introduction of the polymerase chain reaction (PCR) in 1985 opened a new era in analysis of nucleic acids. This technique was soon applied to the detection of potential pathogen DNA and RNA, including viruses, bacteria, and parasites in infectious eye disease. Advances in PCR have allowed class-specific diagnostics (ie, pan-bacterial and pan-fungal), quantitation of pathogen DNA, and multiplexed testing. The Human Genome Project in the early 2000s greatly accelerated development of DNA sequencers, ushering in the era of "Next Generation Sequencing" and permitting pathogen-agnostic methods for the detection of potential infectious agents. Most recently, new technologies such as nanopore sequencing have reduced both cost and equipment requirements for whole-genome sequencing; when coupled with real-time sequence analysis methods, these methods offer the promise of true, real-time, point-of-service ocular infectious disease diagnostics.

CONCLUSIONS

Molecular methods for pathogen detection have greatly advanced the diagnosis of ocular infectious disease. Further methodologic advances will have a direct impact on the management of these conditions.

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.

HYPERAUTOFLUORESCENT SPOTS IN ACUTE OCULAR TOXOPLASMOSIS: A New Indicator of Outer Retinal Inflammation

PURPOSE

The aim of this study was to describe the fundus autofluorescence patterns in acute ocular toxoplasmosis (OT) and to correlate these findings with other imaging.

METHODS

A retrospective multicenter case series of 27 eyes from 27 patients with acute onset of posterior OT was conducted. Multimodal imaging including fundus autofluorescence was performed at diagnosis and during follow-up.

RESULTS

All OT lesions were hypoautofluorescent on fundus autofluorescence imaging. Fourteen patients (51.8%) also had hyperautofluorescent spots around the active foci that disappeared after retinal photobleaching. Although these spots were not seen on early phase of indocyanine green angiography, they become hypofluorescent in the late phase without choriocapillaris flow impairment on optical coherence tomography angiography. On B-scan spectral domain optical coherence tomography, spots corresponded to outer retinal alterations in all cases. All hyperautofluorescent spots disappeared during follow-up as acute OT resolved. Younger patients and those with more posterior inflammatory symptoms (vasculitis and/or papillitis) were more frequent with the presence of hyperautofluorescent spots.

CONCLUSION

Ocular toxoplasmosis may trigger a transient outer retinal disruption in eyes with marked inflammatory symptoms of the younger patients.

Pathophysiological Aspects of Ocular Toxoplasmosis: Host-parasite Interactions

Purpose: This review aims to present the state of the art to understand the pathophysiology of ocular toxoplasmosis (OT), providing further foundations that would help to improve the future treatment and prognosis of this potentially blinding disease.Methods: A thorough literature search was performed in PubMed database. An additional search was made in Google Scholar to complete the collected items.Results: Toxoplasma gondii ocular infection is one of the most frequent causes of posterior uveitis. Despite the ocular barriers, the parasite reaches the eye through different mechanisms. Once inside, it remains encysted livelong within the retina, and recurrences cannot be completely avoided. The complexity of host-parasite interactions, leading to the success of this parasite, encompasses host factors such as genetic predisposition, immune status, and age; and parasite factors such as strain diversity, virulence, phylogenetic origin, and geographical distribution. These factors influence the clinical presentation, course, and progression of the disease. Additional elements, such as pregnancy, eating behavior, and environmental, social, and cultural factors may also contribute to this complex balance.Conclusions: The host-parasite interaction in OT is a complex and multifactorial relationship, with the parasite always on the driving edge of the game. There are still multiple incompletely understood fields to be investigated. Future research would permit further insight into the immune-biology of the parasite and recognition of the host-parasite interplay to improve the diagnostic and management performance.

Interleukins and cytokine biomarkers in uveitis

Interleukins and cytokines are involved in the pathogenesis of uveitis of heterogeneous origin. Understanding the basics of the ocular immune privilege is a fulcrum to discern their specific role in diverse uveitis to potentially translate as therapeutic targets. This review attempts to cover these elements in uveitis of infectious, noninfectious and masquerade origin. Insights of the molecular targets in novel therapy along with the vision of future research are intriguing.

Pathogenesis of ocular toxoplasmosis

Ocular toxoplasmosis is a retinitis -almost always accompanied by vitritis and choroiditis- caused by intraocular infection with Toxoplasma gondii. Depending on retinal location, this condition may cause substantial vision impairment. T. gondii is an obligate intracellular protozoan parasite, with both sexual and asexual life cycles, and infection is typically contracted orally by consuming encysted bradyzoites in undercooked meat, or oocysts on unwashed garden produce or in contaminated water. Presently available anti-parasitic drugs cannot eliminate T. gondii from the body. In vitro studies using T. gondii tachyzoites, and human retinal cells and tissue have provided important insights into the pathogenesis of ocular toxoplasmosis. T. gondii may cross the vascular endothelium to access human retina by at least three routes: in leukocyte taxis; as a transmigrating tachyzoite; and after infecting endothelial cells. The parasite is capable of navigating the human neuroretina, gaining access to a range of cell populations. Retinal Müller glial cells are preferred initial host cells. T. gondii infection of the retinal pigment epithelial cells alters the secretion of growth factors and induces proliferation of adjacent uninfected epithelial cells. This increases susceptibility of the cells to parasite infection, and may be the basis of the characteristic hyperpigmented toxoplasmic retinal lesion. Infected epithelial cells also generate a vigorous immunologic response, and influence the activity of leukocytes that infiltrate the retina. A range of T. gondii genotypes are associated with human ocular toxoplasmosis, and individual immunogenetics -including polymorphisms in genes encoding innate immune receptors, human leukocyte antigens and cytokines- impacts the clinical manifestations. Research into basic pathogenic mechanisms of ocular toxoplasmosis highlights the importance of prevention and suggests new biological drug targets for established disease.

A new era of uveitis: impact of polymerase chain reaction in intraocular inflammatory diseases

Uveitis is a sight-threatening intraocular inflammatory disorder which may occur from both infectious and non-infectious or autoimmune causes. The frequency of infectious uveitis and autoimmune uveitis varies depending on countries and regions. According to a nationwide survey conducted by the Japanese Ocular Inflammation Society, infectious and non-infectious uveitis accounted for 16.4 and 50.1% of new patients, respectively while the remaining 33.5% of new uveitis cases were not classified or were idiopathic uveitis. Infectious uveitis is particularly important because it causes tissue damage to the eye and may result in blindness unless treated. However, it can be treated if the pathogenic microorganisms are identified promptly and accurately. Remarkable advancements in molecular and immunological technologies have been made in the last decade, and the diagnosis of infectious uveitis has been greatly improved by the application of molecular and immunological investigations, particularly polymerase chain reaction (PCR). PCR performed on a small amount of ocular samples provides a prompt, sensitive, and specific molecular diagnosis of pathogenic microorganisms in the eye. This technology has opened a new era in the diagnosis and treatment of uveitis, enabling physicians to establish new clinical entities of uveitis caused by infectious microorganisms, identify pathogens in the eyes of many patients with uveitis, and determine prompt diagnosis and appropriate therapy. Here we review the PCR process, new PCR tests specialized for ocular diseases, microorganisms detected by the PCR tests, diseases in the eye caused by these microorganisms, and the clinical characteristics, diagnosis, and therapy of uveitis.

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.

Toxoplasmosis: A history of clinical observations

It has been 100 years since Toxoplasma gondii was initially described in Tunis by Nicolle and Manceaux (1908) in the tissues of the gundi (Ctenodoactylus gundi) and in Brazil by Splendore (1908) in the tissues of a rabbit. Toxoplasma gondii is a ubiquitous, Apicomplexan parasite of warm-blooded animals that can cause several clinical syndromes including encephalitis, chorioretinitis, congenital infection and neonatal mortality. Fifteen years after the description of T. gondii by Nicolle and Manceaux a fatal case of toxoplasmosis in a child was reported by Janků. In 1939 Wolf, Cowen and Paige were the first to conclusively identify T. gondii as a cause of human disease. This review examines the clinical manifestations of infection with T. gondii and the history of the discovery of these manifestations.

Intraocular inflammation associated with ocular toxoplasmosis: relationships at initial examination

PURPOSE

To describe characteristics of intraocular inflammation in eyes with active ocular toxoplasmosis and to identify relationships between signs of inflammation, complications (including elevated intraocular pressure [IOP]), other disease features, and host characteristics.

DESIGN

Multicenter, retrospective, cross-sectional study.

METHODS

We reviewed the medical records of 210 patients with toxoplasmic retinochoroiditis at seven international sites (North America, South America, and Europe) for information from the first examination at each site during which patients had active retinal lesions. Signs of inflammation included anterior chamber (AC) cells and flare and vitreous humor cells and haze. Retinal lesion characteristics included size (< or =1 disc area [DA] or >1 DA) and presence or absence of macular involvement.

RESULTS

AC cells and flare were related to vitreous inflammatory reactions (P < or = .041). One or more signs of increased inflammation were related to the following factors: older patient age, larger retinal lesions, and extramacular location. In 30% of involved eyes, there was evidence of elevated IOP (despite use of glaucoma medications by some patients); other complications were uncommon. IOP of more than 21 mm Hg was associated with both increased AC cells and elevated flare (both P < or = .001) and with macular involvement (P = .009). Inflammation seemed to be more severe among patients in Brazil than among those at other sites.

CONCLUSIONS

There is substantial variation between patients in the severity of intraocular inflammation associated with ocular toxoplasmosis, attributable to multiple host- and disease-related factors. Results suggest that disease characteristics also vary in different areas of the world. Elevated IOP at initial examination reflects the severity of inflammation.

Longitudinal study of new eye lesions in children with toxoplasmosis who were not treated during the first year of life

PURPOSE

To determine the incidence of new chorioretinal lesions in children with toxoplasmosis diagnosed after, and therefore not treated during, their first year.

DESIGN

Prospective longitudinal cohort study.

METHODS

Thirty-eight children were evaluated in Chicago between 1981 and 2005 for new chorioretinal lesions. Thirty-eight children and mothers had serum IgG antibody to Toxoplasma gondii.

RESULTS

Twenty-eight of 38 children had one of the following: diagnosis with serum antibody to T. gondii indicative of chronic infection at age 24 months, central nervous system calcifications, hydrocephalus, illness compatible with congenital toxoplasmosis perinatally but not diagnosed at that time. Twenty-five returned for follow-up during 1981 to 2005. Their mean (range) age at last exam was 10.9 +/- 5.7 (range, 3.5 to 27.2) years and mean follow-up was 5.7 +/- 2.9 years. Eighteen (72%) children developed at least one new lesion. Thirteen (52%) had new central lesions, 11 (44%) had new peripheral lesions, and six (24%) had both. Thirteen (52%) had new lesions diagnosed at age > or =10 years. New lesions were found at more than one visit in four (22%), and bilateral new lesions developed in seven (39%) of 18 children who developed new lesions. Of 10 additional children with eye findings and serologic tests indicative of chronic infection, six returned for follow-up, four (67%) developing new lesions at > or =10 years of age.

CONCLUSIONS

More than 70% developed new chorioretinal lesions. New lesions were commonly diagnosed after the first decade of life.

Ocular toxoplasmosis: a global reassessment. Part I: epidemiology and course of disease

PURPOSE

To update clinical information about ocular toxoplasmosis. Part I reviews information about prevalence of disease, sources of infection, relation of ocular disease to time of Toxoplasma gondii infection (congenital vs. postnatally acquired), and course of disease.

DESIGN

Literature review.

METHODS

Selected articles from the medical literature, information from recent scientific meetings, and the author's personal experiences were reviewed critically in preparation for the LX Edward Jackson Memorial Lecture.

RESULTS

The prevalence of T. gondii infection varies geographically and increases with age; in the United States, the overall proportion is 22.5%. The proportion of infected individuals in the United States who have had episodes of ocular toxoplasmosis is unknown, but may be approximately 2%. Prevalence of ocular involvement is substantially greater in other parts of the world, including southern Brazil. In addition to undercooked meat and unwashed vegetables, drinking water contaminated with oocysts may be an important source of infection in some settings. In contrast to traditional teaching, evidence suggests that most individuals with ocular toxoplasmosis were infected postnatally. Ocular lesions may first develop many years after T. gondii infection. The risk of recurrent ocular disease appears to be greater during the first year after an episode of toxoplasmic retinochoroiditis than during subsequent years.

CONCLUSIONS

Reassessment of older publications in the light of recent observations provides a richer understanding of ocular toxoplasmosis, although knowledge about the disease remains incomplete. A better understanding of the clinical characteristics and course of ocular toxoplasmosis will have important implications for developing more effective prevention and treatment strategies.

Eye manifestations of congenital toxoplasmosis

PURPOSE

To determine the natural history of treated and untreated congenital toxoplasmosis and impact of this infection on vision.

METHODS

In this prospective, longitudinal study, 76 newborns were treated with pyrimethamine and sulfadiazine for approximately one year, and 18 individuals not treated during their first year of life entered the study after age 1 year (historical patients).

RESULTS

Chorioretinal scars were the most common eye finding in all patients and were most common in the periphery (58% of treated and 82% of historical patients). Macular scars were present in 54% of the treated patients; 41% were bilateral. Macular scars were present in 76% of the historical patients; 23% were bilateral. Visual acuity in the presence of macular lesions ranged from 20/20 to 20/400. Of the patients followed up from the newborn period and treated, 29% had bilateral visual impairment, with visual acuity for the best eye of less than 20/40. Causes for this visual impairment in eyes with quiescent lesions included macular scars, dragging of the macula secondary to a peripheral lesion, retinal detachment, optic atrophy, cataract, amblyopia, and phthisis. There were recurrences in both treated (13%, 7/54) and previously untreated historical patients (44%, 8/18). The total, median, and range of years of follow-up during which recurrences were observed were, for treated patients, 189 years (total), five years (median) and three to ten years (range) and, for historical, untreated patients, 160 years (total), 11 years (median), and three to 24 years (range). New lesions occurred in previously normal retinas and also contiguous to older scars. Active lesions appeared to become quiescent within ten to 14 days after beginning pyrimethamine and sulfadiazine therapy.

CONCLUSION

Many children with congenital toxoplasmosis have substantial retinal damage at birth and consequent loss of vision. Nonetheless, vision may be remarkably good in the presence of large macular scars. Active lesions become quiescent with treatment.

Toxoplasma gondii and ocular toxoplasmosis: pathogenesis

Images

Eye manifestations of congenital toxoplasmosis

PURPOSE

To determine the natural history of treated and untreated congenital toxoplasmosis and impact of this infection on vision.

METHODS

In this prospective, longitudinal study, 76 newborns were treated with pyrimethamine and sulfadiazine for approximately one year, and 18 individuals not treated during their first year of life entered the study after age 1 year (historical patients).

RESULTS

Chorioretinal scars were the most common eye finding in all patients and were most common in the periphery (58% of treated and 82% of historical patients). Macular scars were present in 54% of the treated patients; 41% were bilateral. Macular scars were present in 76% of the historical patients; 23% were bilateral. Visual acuity in the presence of macular lesions ranged from 20/20 to 20/400. Of the patients followed up from the newborn period and treated, 29% had bilateral visual impairment, with visual acuity for the best eye of less than 20/40. Causes for this visual impairment in eyes with quiescent lesions included macular scars, dragging of the macula secondary to a peripheral lesion, retinal detachment, optic atrophy, cataract, amblyopia, and phthisis. There were recurrences in both treated (13%, 7/54) and previously untreated historical patients (44%, 8/18). The total, median, and range of years of follow-up during which recurrences were observed were, for treated patients, 189 years (total), five years (median), and three to ten years (range) and, for historical, untreated patients, 160 years (total), 11 years (median), and three to 24 years (range). New lesions occurred in previously normal retinas and also contiguous to older scars. Active lesions appeared to become quiescent within ten to 14 days after beginning pyrimethamine and sulfadiazine therapy.

CONCLUSION

Many children with congenital toxoplasmosis have substantial retinal damage at birth and consequent loss of vision. Nonetheless, vision may be remarkably good in the presence of large macular scars. Active lesions become quiescent with treatment.

Identification of Toxoplasma gondii in paraffin-embedded sections by the polymerase chain reaction

We used the polymerase chain reaction to amplify DNA fragments specific to Toxoplasma gondii. The sensitivity of the technique allowed for the detection of as few as ten cultured T. gondii tachyzoites. We applied the same amplification technique to deparaffinized ocular sections from two cases of ocular toxoplasmosis. Although toxoplasmic cysts could only be seen in one eye by optical microscopy, polymerase chain reaction allowed the identification of the parasite in both cases. Our study indicates the feasibility of a sensitive DNA-based assay to complement pathologic studies of an ocular parasitic disease.

Treatment of toxoplasmosis with trimethoprim-sulphamethoxazole

Toxoplasmosis is known to complicate diseases with impaired cellular immunity. For treatment of toxoplasma infections atoxic drugs should be used to avoid depression of the bone marrow. The hitherto recommended treatment, pyrimethamine in combination with sulphonamides, is often associated with severe side-effects. The present study presents the results of treatment with trimethoprim and sulphamethoxazole in 7 patients, clinically and serologically diagnosed as having toxoplasmosis. Good therapeutic results were observed in 5 patients with lymphoglandular toxoplasmosis and a significant reduction of the dye test titres were found in 6 patients. In one patient, however, a relapse of clinical symptoms and a reversion to high dye test titres were observed 6 1/2 months after the end of the treatment. Treatment had to be discontinued in one patient due to an allergic reaction.