False Negative Toxoplasma Serology in an Immunocompromised Patient with PCR Positive Ocular Toxoplasmosis

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.

Detection of Parasites in the Field: The Ever-Innovating CRISPR/Cas12a

The rapid and accurate identification of parasites is crucial for prompt therapeutic intervention in parasitosis and effective epidemiological surveillance. For accurate and effective clinical diagnosis, it is imperative to develop a nucleic-acid-based diagnostic tool that combines the sensitivity and specificity of nucleic acid amplification tests (NAATs) with the speed, cost-effectiveness, and convenience of isothermal amplification methods. A new nucleic acid detection method, utilizing the clustered regularly interspaced short palindromic repeats (CRISPR)-associated (Cas) nuclease, holds promise in point-of-care testing (POCT). CRISPR/Cas12a is presently employed for the detection of Plasmodium falciparum, Toxoplasma gondii, Schistosoma haematobium, and other parasites in blood, urine, or feces. Compared to traditional assays, the CRISPR assay has demonstrated notable advantages, including comparable sensitivity and specificity, simple observation of reaction results, easy and stable transportation conditions, and low equipment dependence. However, a common issue arises as both amplification and cis-cleavage compete in one-pot assays, leading to an extended reaction time. The use of suboptimal crRNA, light-activated crRNA, and spatial separation can potentially weaken or entirely eliminate the competition between amplification and cis-cleavage. This could lead to enhanced sensitivity and reduced reaction times in one-pot assays. Nevertheless, higher costs and complex pre-test genome extraction have hindered the popularization of CRISPR/Cas12a in POCT.

CRISPR/Cas12a combined with RPA for detection of T. gondii in mouse whole blood

BACKGROUND

Toxoplasma gondii is an opportunistic protozoan that is ubiquitous in humans and animals. It can invade any human organ and cause severe diseases, including toxoplasma ophthalmopathy, meningoencephalitis, and liver necrosis. Porcine toxoplasmosis is prevalent in China. CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) and Cas (CRISPR-Associated Protein) systems are widely used for gene editing and pathogen detection. CRISPR-based diagnostics are molecular assays that have been developed to detect parasites with high sensitivity and specificity.

METHODS

This study aimed to establish a combined CRISPR/Cas12a and RPA rapid detection method for T. gondii by targeting the B1 gene and 529 bp repeat element (529 RE). The detection results could be visualized by the fluorescence or lateral flow strips (LFS). The sensitivity and specificity of the method were evaluated, and T. gondii-infected mouse blood was used for detection.

RESULTS

The results indicated that the established method for T. gondii detection was satisfactory, with a detection limit of 1.5 cp/μl for the two loci. Moreover, the B1 gene could detect 1 tachyzoite per reaction, and the 529 RE could detect 0.1 tachyzoite per reaction, consistently with the highly sensitive nested polymerase chain reaction (PCR) results. The method was suitable for strains, including RH, and did not cross-react with other protozoa DNA with similar habits. The T. gondii-infected mouse blood samples were all positive for T. gondii at 1, 3, and 5 days post infection (dpi).

CONCLUSIONS

This study established a rapid, sensitive, and time-saving DNA detection method for T. gondii that has the potential to be an alternative tool for T. gondii detection in the field.

Prevalence of Toxoplasmic Retinochoroiditis in an Australian Adult Population: a Community-Based Study

OBJECTIVE

Toxoplasmic retinochoroiditis is the most common clinical manifestation of an infection with the protozoan parasite, Toxoplasma gondii. Up to 50% of the human population is estimated to be infected with T. gondii. However, the epidemiology of toxoplasmic retinochoroiditis is not widely reported. We sought to estimate the prevalence of toxoplasmic retinochoroiditis in Australia using data collected as part of the Busselton Healthy Ageing Study.

DESIGN

Cross-sectional, community-based, prospective cohort study.

PARTICIPANTS

5,020 Australian adults (2,264 men and 2,756 women; age range of 45-69 years and median age of 58 years).

METHODS

Retinal color photographs centered on the optic disc and macula were captured on a digital retinal camera following dilation of the pupils. Three uveitis-subspecialized ophthalmologists assessed each pigmented retinal lesion, and complete concordance of opinion was required to assign a toxoplasmic etiology. Serum T. gondii immunoglobulin (Ig)G levels were measured for those participants with retinal lesions judged to be toxoplasmic retinochoroiditis.

MAIN OUTCOME MEASURES

Prevalence of toxoplasmic retinochoroiditis.

RESULTS

Eight participants (0.16%) had retinal lesions that were considered to have the characteristic appearance of toxoplasmic retinochoroiditis, plus detectable serum T. gondii IgG, consistent with the diagnosis of toxoplasmic retinochoroiditis. On the assumption that 23.81% of retinal lesions occur at the posterior pole, as reported in a community-based survey conducted in Brazil (Sci Rep. 2021;11:3420), the prevalence of toxoplasmic retinochoroiditis was estimated at 0.67% or 1 per 149 persons.

CONCLUSIONS

Toxoplasmic retinochoroiditis is common in Australian adults. Efforts to quantify and address risk factors for human infection with T. gondii are justified.

Primary Toxoplasma gondii infection-associated with hemophagocytic syndrome in a man with HIV infection: a case report

Background

Reactivation of latent Toxoplasma gondii (T. gondii) infection is more common than primary infection in patients with human immunodeficiency virus (HIV). We report a rare case of primary T. gondii infection-associated hemophagocytic syndrome (HPS).

Case presentation

A man with HIV infection presented with fever, dyspnea and pancytopenia. He was diagnosed with primary T. gondii infection by the seroconversion from single-positive IgM antibody to double-positive IgM and IgG antibody. Metagenomic next-generation sequencing (mNGS) of a plasma sample yielded high reads of T. gondii DNA. He responded well to combined anti-Toxoplasma medicines and glucocorticoid treatment.

Conclusions

In patients with HPS and positive T. gondii IgM antibody, mNGS analysis of a peripheral blood sample is helpful in diagnosing disseminated T. gondii infection. The dynamic changes by serological detection for IgM and IgG of T. gondii further supported the inference that the patient has experienced a primary T. gondii infection.

Ocular toxoplasmosis, an overview focusing on clinical aspects

Toxoplasma gondii is a widespread protozoan parasite infecting approximately one third of the world population. After proliferation of tachyzoites during the acute stage, the parasite forms tissue cysts in various anatomical sites and establishes chronic infection. Nowadays the nature of the interplay between the protozoan and its human host remains elusive. This is clearly evident in ocular toxoplasmosis, in which the parasite establishes an ambivalent relationship with the eye, manipulating the immune response and inducing variable initial lesions and further relapses. This review will focus on epidemiology and environmental, parasite and host related risk factors, clinical manifestations and laboratory findings, treatment and prophylaxis approaches in ocular toxoplasmosis. An image collection of patients referred to the Unit of Ophthalmology of Pisa's Hospital will be presented, too.

ATYPICAL FORMS OF EYE TOXOPLASMOSIS IN CHILDHOOD. CASE REPORTS

AIM

To present an outline of acquired atypical forms of ocular toxoplasmosis (OT) in childhood, with reference to the 100th anniversary of the discovery of this etiology by Professor Janků from Czechoslovakia, who was first to describe the clinical congenital picture of OT characterised by macular scar.

MATERIAL AND METHODS

Symptoms of intraocular bilateral neuritis appeared in a 6-year-old girl, with visual acuity (VA) bilaterally 0.1. Toxoplasmic etiology was demonstrated in laboratory tests, and the patient was immunocompetent. Following treatment with macrolide antibiotic and parabulbar application of corticosteroid, the condition was normalised stably at VA 1.0 in both eyes. Bilateral retinal vasculitis was determined in an 8-year-old boy, with VA of 0.25 in the right eye and 0.25 in the left, with a medical history of strabismus detected after suffering from varicella. The examination for toxoplasmosis was negative, but pronounced general hypogammaglobulinaemia classes IgG, IgM and IgA was detected. Immunosuppressive and immunomodulatory therapy did not produce the desired effect, and the condition progressed to retinochoroiditis. Due to blindness and dolorous glaucoma, enucleation of the right eye was performed at the age of 15 years. Histologically toxoplasmic cysts with bradyzoites were detected, a subsequent laboratory test demonstrated toxoplasmic etiology upon a background of persistent regressing hypogammaglobulinaemia. General anti-toxoplasma and subsequent immunosuppressive treatment did not produce the desired effect, and at the age of 22 years the patient lost his sight also in the left eye.

CONCLUSION

Atypical form of OT intraocular neuritis in an immunocompetent patient had a favourable course, whereas retinal vasculitis with retinochoroiditis in a temporarily immunocompromised patient ended in bilateral blindness.

Practical Guidance for Clinical Microbiology Laboratories: Diagnosis of Ocular Infections

The variety and complexity of ocular infections have increased significantly in the last decade since the publication of Cumitech 13B, Laboratory Diagnosis of Ocular Infections (L. D. Gray, P. H. Gilligan, and W. C. Fowler, Cumitech 13B, Laboratory Diagnosis of Ocular Infections, 2010). The purpose of this practical guidance document is to review, for individuals working in clinical microbiology laboratories, current tools used in the laboratory diagnosis of ocular infections. This document begins by describing the complex, delicate anatomy of the eye, which often leads to limitations in specimen quantity, requiring a close working bond between laboratorians and ophthalmologists to ensure high-quality diagnostic care. Descriptions are provided of common ocular infections in developed nations and neglected ocular infections seen in developing nations. Subsequently, preanalytic, analytic, and postanalytic aspects of laboratory diagnosis and antimicrobial susceptibility testing are explored in depth.

Ocular Toxoplasmosis Mimicking Lymphoma: Exploring the Correlation and Distinction

We present a case of a 74-year-old woman with chronic lymphocytic leukemia (CLL) who presented with unilateral blurry vision that had progressively worsened over a few weeks. Ophthalmic examination revealed unilateral anterior chamber, vitreous body inflammation along with retinal infiltration which was initially diagnosed with posterior uveitis. Analysis of vitreous fluid aspiration was negative for bacteria, fungal and viral etiologies. Despite the broad-spectrum intraocular antibiotics, her vision continued to decline, and she later developed retinal detachment. Cytology for lymphoma was negative. However, polymerase chain reaction (PCR) with internal transcribed spacer-specific (ITS) primer set detected Toxoplasma gondii, and the patient was diagnosed with intraocular toxoplasmosis. Treatment with systemic clindamycin, pyrimethamine, leucovorin, prednisone, and topical clindamycin for four weeks successfully prevented further ocular damage. 

Seronegative ocular toxoplasma panuveitis in an immunocompetent patient

Purpose

Toxoplasma gondii is the most common cause of infectious posterior uveitis worldwide in immunocompetent patients. Despite its prevalence, diagnosis can still be challenging and vision-threatening in cases with atypical presentations. This case exemplifies the importance of clinical exam and additional workup when required despite negative initial serology results.

Observations

A 73-year-old immunocompetent woman presented with a 2-year history of recurrent panuveitis and retinal necrosis not responsive to systemic antiviral therapy. Toxoplasma serum antibodies (IgG and IgM) were not detected on systemic workup one year prior. The slit-lamp exam revealed mutton fat keratic precipitates, panuveitis, and necrotic retinal lesions adjacent to a retinal scar. Repeated Toxoplasma serum antibodies (IgG and IgM) were again negative. However, aqueous fluid testing by polymerase chain reaction (PCR) was highly positive for Toxoplasma gondii. The patient improved after starting systemic anti-toxoplasma therapy.

Conclusion/Importance

To our knowledge, this is the first report in the literature of an immunocompetent patient with ocular toxoplasmosis and undetectable serum IgG and IgM. Aqueous fluid PCR testing is useful in suspected ocular toxoplasmosis in patients with vision-threatening lesions despite negative serology.

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This is the first report in the English literature of seronegative ocular toxoplasmosis in an immunocompetent patient.

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Diagnosis of ocular toxoplasmosis can be challenging.

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Clinical exam and additional workup still have a role in excluding ocular toxoplasmosis in immunocompetent patients.

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Treatment is recommended in vision-threatening infections.

When biology supports clinical diagnosis: review of techniques to diagnose ocular toxoplasmosis

Toxoplasmosis is a common infection whose worldwide prevalence is estimated at 30%, with large disparities across the world. Among infected subjects, the prevalence of ocular toxoplasmosis (OT) is, however, limited to about 2% in Europe and 17% in South America. In France, it is estimated that about 1 000 000 patients present either active OT or subsequent chorioretinal scars. Toxoplasmagondii is the first cause of posterior uveitis worldwide, responsible for retinochoroiditis, at times associated with anterior uveitis. To date, there is no consensus yet on how to diagnose OT, which is often based only on clinical presentation. Nevertheless, OT-associated symptoms are often atypical and misleading. Over the last 20 years, tremendous progress has been made in biological tools, enabling parasitologists to confirm the diagnosis in most suspected cases of OT. Using anterior chamber puncture, a safe and fast procedure, ophthalmologists sample aqueous humour for analysis using multiple techniques in order to reach high specificity and sensitivity in OT diagnosis. In this article, we present the different techniques available for the biological diagnosis of OT, along with their characteristics, and propose a diagnostic algorithm designed to select the best of these techniques if clinical examination is not sufficient to ascertain the diagnosis.