Human toxoplasmosis: which biological diagnostic tests are best suited to which clinical situations?

Abstract

The Toxoplasma gondii parasite is a worldwide threat most particularly in fetal life and immunosuppression. In most clinical situations (except in some ocular cases), correct detection or identification of toxoplasmosis requires biological analysis. This article considers the laboratory tools that have been developed in this field since the discovery of the pathogen, with emphasis on the most recent tests and how they can or should be used in different clinical situations. The authors also discuss the requirements and pitfalls that one should be aware of when biologically investigating this intriguing parasitosis.

Keywords::

• confirmatory test
• congenital
• diagnosis
• immunosuppression
• screening
• Toxoplasma gondii
• uveitis

Financial & competing interests disclosure

The Grenoble Laboratory of Parasitology and Mycology (including all the authors) has received funding from bioMérieux, Abbott Laboratories and Roche Diagnostics. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Writing assistance was provided by Linda Northrup (English Solutions, Voiron, France).

Key issues

• • Because toxoplasmosis is a worldwide issue, policy on this disease differs substantially among countries, notably concerning diagnostic strategies.

• • Delay in diagnosis can result in poor outcome and the need for expensive measures, whereas optimized procedures are thought to be able to prevent the main deleterious consequences, for individuals and for society.

• • In nearly all clinical situations, accurate detection and identification of toxoplasmosis require biological tools.

• • Screening pregnant women for detection of primary infection has decreased congenital toxoplasmosis incidence in several countries, although a few authors do not agree with this general consensus.

• • Serological methods are numerous, and adequate interpretation requires experience and rigorous procedures.

• • Evidence of the presence of active parasites, for diagnosis in immunosuppressed patients as well as in ocular toxoplasmosis, is now mostly provided by molecular methods.

• • These molecular methods generally consist of in-house PCR, explaining the heterogeneity in performance among laboratories. However, international studies and quality-control programs will improve the accuracy of PCR.

Notes

EIA: Immunoenzymatic assay; IB: Immunoblotting assay; IFA: Immunofluorescent assay; qPCR: Quantitative real-time PCR.