Contribution of laboratory methods in diagnosing clinically suspected ocular toxoplasmosis in Brazilian patients

Abstract

This prospective study evaluated the value of laboratorial diagnosis in ocular toxoplasmosis analyzing peripheral blood samples from a group of Brazilian patients by immunologic and molecular methods. We analyzed blood samples from 184 immunocompetent patients with ocular disorders divided into 2 groups: Group I, composed of samples from 49 patients with ocular toxoplasmosis diagnosed by clinical features; Group II, samples from 135 patients with other ocular diseases. Samples were assayed by conventional polymerase chain reaction (cnPCR), real-time PCR (qPCR) for Toxoplasma gondii, indirect immunofluorescence reaction (IF), avidity test (crude tachyzoite lysate as antigen), and excreted–secreted tachyzoite proteins as antigen (ESA-ELISA). cnPCR and qPCR profiles were concordant in all samples. Positive PCR was shown in 40.8% of group I patients. The majority of the positive blood samples (75%) were taken from patients with toxoplasmic retinochoroiditis scars, and the others (25%), from patients with retinal exudative lesions. Despite that 86 of the 135 patients from Group II had asymptomatic toxoplasmosis, all DNA blood samples had negative PCR. Concordant results were shown in the data obtained by serologic methods. Around 24% of the patients with ocular toxoplasmosis had high antibody titers determined by ESA-ELISA and IF. Anti-ESA antibodies are shown principally in patients with active infection. Collectively, these data demonstrate the presence of tachyzoites in the blood of patients with chronic infection, supporting the idea of recurrent disease. Circulating parasites in blood of immunocompetent individuals may be associated with the reactivation of the ocular disease.

Introduction

Toxoplasmic retinochoroiditis is the most common lesion caused by Toxoplasma gondii infection and may occur either immediately or long after the initial infection or in reactivation (Montoya and Remington, 1996, Vallochi et al., 2008). Rupture of dormant cysts in the retina can release viable parasites that induce necrosis and inflammation. Alternatively, retinochoroiditis might result from a hypersensitivity reaction triggered by unknown causes (Commodaro et al., 2009), resulting in irreversible damage to the retina involved, whose consequences may be severe visual morbidity (Remington et al., 2001). In addition, toxoplasmic retinochoroiditis has been reported as more severe in Brazil than in Europe (Gilbert et al., 2008).

Despite the diagnosis of ocular toxoplasmosis is typically based on clinical analysis, the laboratorial tests normally can help the definitive diagnosis. The presence of anti–T. gondii IgG antibodies does not confirm the toxoplasmic etiology, but such antibodies can often persist at high titers for years after the acute infection, and a negative result generally discards the diagnosis (Ongkosuwito et al., 1999). T. gondii DNA has been identified in ocular tissue sections and vitreous fluid (Grigg et al., 2001, Montoya and Remington, 1996, Rothova et al., 2008).

To evaluate the value of the laboratorial diagnosis in ocular toxoplasmosis, this study analyzed peripheral blood samples from a group of Brazilian patients with ocular toxoplasmosis by immunologic and molecular methods.