Assay Sheet
Test ID
2200 Toxoplasma gondii Real-time qPCR
CPT Code
87799
Clinical Utility
Toxoplasma gondii is highly problematic when primary infection occurs during the first trimester of pregnancy, often leading to fetal death or when reactivation occurs in immunocompromised patients, leading to life-threatening disease including encephalitis and extracerebral toxoplasmosis. Onset of disease in most patients is preceded by an increase in parasite load measured in peripheral blood specimens using quantitative PCR. Monitoring blood levels of Toxoplasma gondii DNA correlates well with treatment.
Procedure
Extraction of Toxoplasma gondii DNA from blood, CSF, other biological fluids, or tissues followed by amplification and detection using real-time, quantitative PCR. An internal control is added to ensure the extraction was performed correctly and the PCR reaction was not inhibited.
Specimen type & specimen handling
Whole Blood: 2 mls collected in EDTA or ACD tube. Ship at ambient temperature Monday thru Friday. Do not centrifuge or freeze. Specimen must be received within 96 hrs of collection.
Amniotic Fluid: 2 mls collected in a sterile, screw top tube. Ship at ambient temperature Monday thru Friday. Specimen must be received within 96 hrs of collection.
CSF: 2 mls collected in a sterile, screw top tube. Freeze and ship on dry ice Monday thru Friday. Specimen must be received within 96 hrs of collection.
Tissue: Place in sterile, screw top container; add small amount of sterile saline to keep moist. Paraffin embedded tissue is acceptable. Ship at ambient temperature Monday thru Friday. Fresh tissue must arrive within 96 hrs of collection.
Call ViraCor for authorization prior to sending any specimen type other than those listed above.
If another specimen type has received authorization for testing the following comment will appear in the final report: "The clinical utility of this result has not yet been demonstrated in the peer reviewed literature and is therefore unknown."
Causes for rejection
Whole blood frozen
Call ViraCor at 800-305-5198 if specimen is greater than 96 hrs old
Specimen types other than those listed above that were sent without prior authorization
Specificity
The primers and probes used in this assay are specific for known Toxoplasma gondii strains based on similarity search algorithms. Additionally, no cross reactivity was detected with any viral or protozoa pathogens.
Toxoplasma gondii Assay Range
500 copies/ml to 1 x 1010 copies/ml
Tissue specimen results will be normalized to copies/1,000 cells
Turnaround Time
Same day (within 8 to 12 hours of receiving specimen), Monday through Saturday
Shipping
Ship Monday through Friday. Friday shipments must be labeled for Saturday delivery. All specimens must be labeled with patient's name and collection date. Multiple tests can be run on one specimen.
Ship specimens FedEx Priority Overnight® to:
ViraCor Laboratories, 1001 NW Technology Dr, Lee's Summit, MO 64086
The CPT codes provided are based on ViraCor’s interpretation of the American Medical Association’s Current Procedural Terminology (CPT) codes and are provided for informational purposes only. CPT coding is the sole responsibility of the billing party. Questions regarding coding should be addressed to your local Medicare carrier. ViraCor assumes no responsibility for billing errors due to reliance on the CPT codes illustrated in this material. PCR tests are performed pursuant to a license agreement with Roche Molecular Systems, Inc. This assay was developed and the performance characteristics were determined at ViraCor Laboratories. This test is performed in a CLIA certified laboratory. FDA approval is not required for the performance of this test.
AS17-0808
Pathogen Overview
ABOUT TOXOPLASMA GONDII ORGANISM
Toxoplasma gondii is an obligate intracellular protozoan ubiquitous in birds and mammals. Toxoplasmosis is the disease that occurs when T. gondii invades and multiplies asexually as tachyzoites within the cytoplasm of nucleated cells. When host immunity develops, multiplication of tachyzoites ceases and tissue cysts form, which remain latent, especially in the brain and muscle. Sexual reproduction of T. gondii occurs only in the intestinal tract of cats; the resultant oocysts passed in the feces remain infectious up to a year in soil, depending upon the temperature and moisture content.
The 2 major routes of transmission in humans are oral and congenital. Humans become infected with T. gondii through direct contact with oocysts in cat feces or through eating meat contaminated with the extraintestinal form of T. gondii. Transmission of the infection from mother to fetus occurs almost solely in women who acquire the infection during pregnancy.
Nearly one quarter of adults and adolescents in the United States have been infected with T. gondii; the incidence of seropositivity increases with increasing age. The diagnosis of toxoplasmosis is most critical in 4 groups of patients: pregnant women who acquire infection during gestation, fetuses and newborns who are congenitally infected, immunocompromised patients, and patients with chorioretinitis.
TOXOPLASMA GONDII CLINICAL MANIFESTATIONS
Infections in healthy individuals are typically asymptomatic or associated with self-limited symptoms, such as fever, malaise, and lymphadenopathy, which usually resolves within weeks to months and does not require treatment. Infections in pregnant women, also asymptomatic, can be transplacentally transmitted to the fetus. If the fetus is infected in the first trimester, the result ranges from severe disease to spontaneous abortion or stillbirth; if infection occurs afterwards, disease manifestations can include encephalitis, mental retardation, blindness, and epilepsy.
Immunocompromised patients are at risk for primary infection or reactivation of latent infection. Transmission of T. gondii by organ transplantation from a seropositive donor to a seronegative recipient is an important potential cause of primary infection in solid organ transplant patients. Hematopoietic stem cell transplant patients and AIDS patients are at most risk for reactivation of a latent infection. Primary toxoplasmosis has been documented between day 1 and 13 months post-transplant; reactivations have been documented up to 7 years post-transplant. Interestingly, toxoplasmosis is sometimes seen only after prophylaxis for pneumocystis pneumonia (PCP) ceases, since the 2 diseases share therapeutic regimens. Common reactivated infections in transplant patients include disseminated toxoplasmosis, cerebral toxoplasmosis, pulmonary toxoplasmosis, and, occasionally, combined ocular and cerebral toxoplasmosis.
Diagnosis is especially difficult in immunocompromised patients, as clinical presentation varies and is often nonspecific. The most common symptoms are fever and altered mental state; pneumonitis and myocarditis are less common presentations. Patients with disseminated toxoplasmosis present with fever that is unresponsive to antibiotics, weakness, and fatigue. Chorioretinitis or multiorgan involvement presenting with acute respiratory failure and haemodynamic abnormalities similar to septic shock may also occur. Cerebral toxoplasmosis, the most common form of infection, presents as mental confusion, seizures, and typical deep-seated lesions of the brain. Disseminated cerebral infections may present with a radiological image of small miliary lesions. Pulmonary toxoplasmosis presents as respiratory distress and lesions in the lungs.
TOXOPLASMA GONDII LABORATORY DIAGNOSIS
T. gondii cannot be cultured in the clinical diagnostic setting, so serological testing has been the mainstay of toxoplasmosis diagnosis, though the method has many significant limitations. For example, IgG antibody detection can be used to identify immunocompromised patients at risk of reactivation but not for diagnosis of current toxoplasmosis, since any exposure to T. gondii at any point in time will result in positive antibodies. Discrimination between recent and more distant infections is not possible using serological methods. In immunocompromised patients, absence of specific antibodies does not rule out active disease since these patients may not be able to mount an appropriate humoral immune response. Risk for congenital toxoplasmosis may go undetected if the pregnant mother was tested during the active phase of infection, when IgG or IgM antibodies may not be detectable. An additional diagnostic method is microscopic examination of tissue, which can be very challenging to obtain. In cases of disseminated toxoplasmosis, the infected tissue could be in almost any organ.
Quantitative, real-time polymerase chain reaction (PCR) overcomes the limitations of serological testing and is a recent and very promising option. It has been shown to be a highly sensitive, specific, and rapid method to detect T. gondii DNA from a wide variety of specimen sources. In addition, monitoring levels of T. gondii DNA in patients correlates well with treatment, enabling physicians to track response to therapy over time and assess outcomes.
TOXOPLASMA GONDII TREATMENT
Transplant recipients most likely to acquire infection via the allograft should be tested for baseline toxoplasma IgG antibodies, along with the donor. A seropositive donor and seronegative recipient are at the highest risk; therefore, the transplant recipient should receive prophylaxis.
A combination of pyrimethamine and sulfonamides is the best evaluated therapy and is recommended as first line therapy. However, not all patients can tolerate this combination; therefore, pyrimethamine and clindamycin in combination are recommended as second-line therapy. After treatment of the acute phase infection, secondary prophylaxis should be administered as maintenance therapy, which usually consists as the same regimen at half doses until underlying immunosuppression has ceased.
Management of maternal and fetal infection varies widely. Spiramycin is often administered after diagnosis of a recently acquired maternal infection.
Selected References
Jones J, Kruszon-Moran D, Wilson M. Toxoplasma gondii infection in the United States, 1999–2000. Emerg Infect Dis. 2003;9(11):1371-1374.
Jones J, Lopez A, Wilson M, et al. Congenital toxoplasmosis: a review. Obstet Gynecol Surv. 2001;56(5):296-305.
Lin M, Chen T, Kuo T, et al. Real-time PCR for quantitative detection of Toxoplasma gondii. J Clin Mirobiol. 2000;38(11):4121-4125.
Martino R, Bretagne S, Einsele H, et al. Early detection of toxoplasma infection by molecular monitoring of Toxoplasma gondii in peripheral blood samples after allogeneic stem cell transplantation. Clin Infect Dis. 2005;(40):67-78.
Montoya J, Liesenfeld O. Toxoplasmosis. Lancet. 2004;(363):1965-1976.
Remington J, Thulliez P, Montoya J. Recent developments for diagnosis of toxoplasmosis. J Clin Microbiol. 2004;2(3):941-945.
Wulf M, Crevel R, Portier R, et al. Toxoplasmosis after renal transplantation: implications of a missed diagnosis. J Clin Microbiol. 2005;43(7):3544-3547.
PAO-16-08007 PCR tests are performed pursuant to a license agreement with Roche Molecular Systems, Inc.
Abstracts & Publications
Jones J, Kruszon-Moran D, Wilson M. Toxoplasma gondii infection in the United States, 1999–2000. Emerg Infect Dis. 2003;9(11):1371-1374.
Jones J, Lopez A, Wilson M, et al. Congenital toxoplasmosis: a review. Obstet Gynecol Surv. 2001;56(5):296-305.
Lin M, Chen T, Kuo T, et al. Real-time PCR for quantitative detection of Toxoplasma gondii. J Clin Mirobiol. 2000;38(11):4121-4125.
Martino R, Bretagne S, Einsele H, et al. Early detection of toxoplasma infection by molecular monitoring of Toxoplasma gondii in peripheral blood samples after allogeneic stem cell transplantation. Clin Infect Dis. 2005;(40):67-78.
Montoya J, Liesenfeld O. Toxoplasmosis. Lancet. 2004;(363):1965-1976.
Remington J, Thulliez P, Montoya J. Recent developments for diagnosis of toxoplasmosis. J Clin Microbiol. 2004;2(3):941-945.
Wulf M, Crevel R, Portier R, et al. Toxoplasmosis after renal transplantation: implications of a missed diagnosis. J Clin Microbiol. 2005;43(7):3544-3547.
