Toxoplasma gondii, Molecular Detection, PCR
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Toxoplasma gondii is an intracellular protozoan parasite that chronically infects about 10% of the adult population in the United States. Transmission may occur by ingestion of undercooked meat containing cysts, by direct contact with the feces of an infected cat excreting infectious oocysts, and vertically through the placenta. Accurate diagnosis is crucial because of the different therapeutic options.
Central nervous system (CNS) toxoplasmosis most often occurs as a complication of HIV infection. Diagnosis of CNS toxoplasmosis is difficult by serologic methods, and direct detection of the organism in cerebrospinal fluid (CSF) by stain and culture is not sensitive. PCR detection of Toxoplasma gondii DNA in CSF is a rapid, sensitive, and specific method for the diagnosis of CNS toxoplasmosis.
Diagnosing central nervous system toxoplasmosis
A positive result indicates presence of DNA from Toxoplasma gondii.
Negative results indicate absence of detectable DNA but does not exclude the presence of organism or active or recent disease.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This assay is designed to detect only species of clinical significance and is to be used for patients with a clinical history and symptoms consistent with toxoplasmosis. This test should not be used to screen healthy patients. Depending on the population, varying percentages of patients may be found to be positive.
Results should be interpreted with consideration of clinical and laboratory findings. A negative result does not indicate absence of disease. Reliable results depend on adequate specimen collection and the absence of inhibiting substances.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Negative for the presence of Toxoplasma gondii DNA
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Luft BJ, Remington JS: Toxoplasmic encephalitis in AIDS. Clin Infect Dis 1992 Aug;15(2):211-222
2. Sterkers Y, Varlet-Marie E, Marty P, et al: Diversity and evolution of methods and practices for the molecular diagnosis of congenital toxoplasmosis in France: a four years survey. Clin Microbiol Infect 2009 Nov 2
3. Villard O, Filisetti D, Roch-Deries F, et al: Comparison of enzyme-linked immunosorbent assay, immunoblotting, and PCR for diagnosis of toxoplasmic chorioretinitis. J Clin Microbiol 2003 Aug;41(8):3537-3541
4. Jones JL, Kruszon-Moran D, Sanders-Lewis K, Wilson M: Toxoplasma gondii infection in the United States, 1999-2004, decline from the prior decade. Am J Trop Med Hyg 2007 Sep;77(3):405-10