[Contribution of gene amplification in the biological diagnosis of toxoplasmosis].

Biological diagnosis of toxoplasmosis is generally based on indirect arguments (serology). In cases of immaturity or of immune depression, however, evidence of the parasite has to be obtained. This involves time-consuming or relatively insensitive culture techniques. Molecular biology, and more particularly the polymerase chain reaction gene amplification technique, makes it possible to identify an extremely small quantity of parasites in a complex biological fluid in a few hours. We summarized our experience with an original technique using toxoplasma ribosomal DNA as the target. Its use in the amniotic fluid provides a distinct improvement in antenatal diagnosis and is fast becoming the technique of reference. Difficult cases have been solved by its application in ophthalmology. Finally, in immunodepressed patients, especially in cases of acquired immunodeficiency syndrome, assessment is currently ongoing. The results obtained so far, especially in the analysis of the cerebral spinal fluid, are encouraging.