Toxoplasmic encephalitis: the use of stage-specific gene as a diagnostic tool.

Abstract

Toxoplasmic encephalitis (TE), a life threatening disease in immuno-compromised hosts, is caused by reactivation of dormant bradyzoites into rapidly dividing tachyzoites of Toxoplasma gondii. Definite diagnosis could not be made by only one method. Presumptive diagnosis is mainly based on central nervous system manifestations, suggestive neuro-imaging features, sero- positive T. gondii antibodies and therapeutic response to anti-toxoplasmic drugs. Over three decades, PCR-based techniques have been introduced and found to be useful for the diagnosis of parasitic infections including Toxoplasma. However, it could not differentiate between bradyzoite and tachyzoite state. Recently, many stage specific genes of T. gondii have been identified along with the development of molecular technologies. Reverse transcriptase-polymerase chain reaction (RT-PCR) is an efficient assay to detect the expression of bradyzoite (BAG1) and tachyzoite (SAG1) specific genes during stage conversion. In addition, this assay could identify the process of re-differentiation from bradyzoites into tachyzoites at the earliest stage, enabling the prophylaxis or treatment of patients in time before the occurrence of severe clinical manifestations. Moreover, the duplex RT-PCR could be further developed to offer a rapid, sensitive, easy-to-handle and reproducible method. Thus the RT-PCR technique may serve as an alternative tool to diagnose TE in severely immuno-compromised patients in the next decade.