Use of TsolR13, a Novel qPCR Biomarker, to Diagnose Neurocysticercosis

TsolR13 is a novel real-time quantitative polymerase chain reaction (qPCR) target and may be a useful tool for diagnosing neurocysticercosis from plasma and cerebrospinal fluid (CSF), according to study results published in Clinical Infectious Diseases.

As a result of seizures caused by cysts found within brain parenchyma, global disability-adjusted life years due to neurocysticercosis is conservatively estimated at 2.8 million years. Further, this estimate does not account for disability caused by the most severe forms of the disease, which include ventricular neurocysticercosis disease and subarachnoid neurocysticercosis. Currently, serologic testing and imaging are used for the diagnosis of subarachnoid neurocysticercosis disease and ventricular neurocysticercosis; however, serology can only demonstrate parasite exposure, not disease severity, and imaging is frequently non-specific and can miss abnormalities associated with these 2 disease states.  

Given the reproducibility, specificity, scalability, and ability to test any tissue sample following DNA extraction, qPCR presents a viable platform for biomarker and diagnostic development. Therefore, this study identified highly repetitive Taenia solium sequences as biomarkers and developed a highly sensitive and specific qPCR method for detection of these biomarkers in plasma and CSF samples to aid in the diagnosis of ventricular neurocysticercosis and subarachnoid neurocysticercosis.

There were 13 candidate repeat sequences in the T solium genome; however, TsolR13 had the best efficiency in qPCR (98.25%) and thus was selected for additional clinical testing. A total of 43 patients —63.6% male — with subarachnoid and/or ventricular neurocysticercosis who had plasma and/or CSF samples at criteria-specific time points for active and/or cured disease were included in the study. 

Subarachnoid involvement of the sylvian fissure and/or basilar area of the brain was present in 68.2% of patients and ventricular disease was found in 31.8% of patients. A total of 82 samples from these patients were included in the study: 46 plasma samples and 36 CSF samples.

The analytic sensitivity of TsolR13 was 97.3% and the analytic specificity was 100%. Further, the clinical sensitivity in detecting active subarachnoid or ventricular disease in symptomatic patients was 81.3% in plasma and 100% in CSF. The predictive ability to distinguish active from cured disease was better for CSF than for plasma (in 94.4% vs 86.7% of patients cured qPCR was negative, respectively). Plasma/serum TsolR13 qPCR negativity as a test of cure showed a predictive value of 80.7%, which suggests plasma may be useful for establishing the diagnosis of neurocysticercosis. However, T solium DNA was detected in the plasma of 28% of patients during long-term follow-up, suggesting that qPCR plasma assessment may not be useful in the long-term monitoring of disease activity.

Overall, the study authors concluded that, “[W]e have developed a widely adaptable, scalable, sensitive and specific qPCR assay that may be used for both the diagnosis and disease monitoring in subarachnoid and ventricular [neurocysticercosis].”

Reference

O’Connell EM, Harrison S, Dahlstrom E, Nash T, Nutman TB. A novel, highly sensitive qPCR assay for the diagnosis of subarachnoid and ventricular neurocysticercosis and for assessing response to treatment [June 21, 2019]. Clin Infect Dis. doi:10.1093/cid/ciz541/5522280