[Direct detection of toxoplasma in the aqueous humor by gene amplification]

For immunocompetent patients, ocular toxoplasmosis is the most frequent infectious cause of chorioretinal inflammation. Nowadays, the laboratory diagnosis of ocular toxoplasmosis requires serological tests and anterior chamber puncture to detect the local production of specific antibodies. The authors describe a new technique to detect toxoplasma in aqueous humor by a polymerase chain reaction in which the target is a 88 bp specific rDNA fragment. 31 patients were concerned (23 highly suspect of ocular toxoplasmosis and 8 controls). The presence of the parasite in aqueous humor was found in 7 cases. No false positive was detected. The sensitivity of the test is reduced by the poor volume of the sample. The combination of this technique with Desmont's coefficient gives a better positive predictive value. We emphasize the pathophysiological value of this technique by suggesting the presence of tachizoites in the anterior chamber. According to our knowledge, this finding has never been demonstrated. In the future, this should be a very promising technique for the diagnosis of ocular toxoplasmosis.