Performance Testing of PCR Assay in Blood Samples for the Diagnosis of Toxoplasmic Encephalitis in AIDS Patients from the French Departments of America and Genetic Diversity of Toxoplasma gondii: A Prospective and Multicentric Study.

Daniel Ajzenberg,Stéphane Simon,Nicole Desbois-Nogard,Patrice Massip,Anaïs Labrunie,Rachida Boukhari,Michel Dupon,Cyrille Vautrin,André Cabié,Isabelle Lamaury,Magalie Demar,Muriel Nicolas,Homayoun Riahi,Marie-Laure Dardé,Marie-Paule Boncoeur,Pierre-Marie Preux

doi:10.1371/journal.pntd.0004790

Abstract

BackgroundToxoplasmic encephalitis in patients with AIDS is a life-threatening disease mostly due to reactivation of Toxoplasma gondii cysts in the brain. The main objective of this study was to evaluate the performance of real-time PCR assay in peripheral blood samples for the diagnosis of toxoplasmic encephalitis in AIDS patients in the French West Indies and Guiana.Methodology/Principal FindingsAdult patients with HIV and suspicion of toxoplasmic encephalitis with start of specific antitoxoplasmic therapy were included in this study during 40 months. The real-time PCR assay targeting the 529 bp repeat region of T. gondii was performed in two different centers for all blood samples. A Neighbor-Joining tree was reconstructed from microsatellite data to examine the relationships between strains from human cases of toxoplasmosis in South America and the Caribbean. A total of 44 cases were validated by a committee of experts, including 36 cases with toxoplasmic encephalitis. The specificity of the PCR assay in blood samples was 100% but the sensitivity was only 25% with moderate agreement between the two centers. Altered level of consciousness and being born in the French West Indies and Guiana were the only two variables that were associated with significantly decreased risk of false negative results with the PCR assay.Conclusion/SignificanceOur results showed that PCR sensitivity in blood samples increased with severity of toxoplasmic encephalitis in AIDS patients. Geographic origin of patients was likely to influence PCR sensitivity but there was little evidence that it was caused by differences in T. gondii strains.Trial RegistrationClinicalTrials.gov NCT00803621

Highlights

The protozoan Toxoplasma gondii is a cosmopolitan parasite that virtually infects all warmblooded animals, including humans who become infected postnatally by ingesting tissue cysts from undercooked meat, consuming food contaminated with oocysts, or by accidentally ingesting oocysts from the environment [1]
The use of PCR testing in blood samples for the diagnosis of Toxoplasmic encephalitis (TE) has been limited by its poor sensitivity in the studies conducted in Europe
Considering that T. gondii strains from tropical South America have substantial genetic and pathogenic differences with those from USA and Europe, it is important to re-evaluate the performance of the PCR assay in blood samples for the diagnosis of TE in AIDS patients from this region

Summary

Introduction

The protozoan Toxoplasma gondii is a cosmopolitan parasite that virtually infects all warmblooded animals, including humans who become infected postnatally by ingesting tissue cysts from undercooked meat, consuming food contaminated with oocysts, or by accidentally ingesting oocysts from the environment [1]. The clinical and radiological response to specific therapy is still the gold standard for confirming a posteriori the diagnosis of TE in AIDS patients. This presumptive diagnosis has important limitations since up to 40% of AIDS patients with suspected TE and treated with specific therapy could not have TE [10]. Toxoplasmic encephalitis in patients with AIDS is a life-threatening disease mostly due to reactivation of Toxoplasma gondii cysts in the brain. The main objective of this study was to evaluate the performance of real-time PCR assay in peripheral blood samples for the diagnosis of toxoplasmic encephalitis in AIDS patients in the French West Indies and Guiana.

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