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| COMMENTARY |
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| Year : 2020 | Volume
: 68
| Issue : 6 | Page : 1331-1332 |
Diagnosis CNS Viral Infections by Real-Time PCR: Further Exploration Needed
Ravindra Kumar Garg, Hardeep Singh Malhotra
Department of Neurology, King George Medical University, Lucknow, Uttar Pradesh, India
| Date of Web Publication | 19-Dec-2020 |
Correspondence Address:
Dr. Ravindra Kumar Garg
Department of Neurology, King George Medical University, Lucknow, Uttar Pradesh
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0028-3886.304086
How to cite this article:
Garg RK, Malhotra HS. Diagnosis CNS Viral Infections by Real-Time PCR: Further Exploration Needed. Neurol India 2020;68:1331-2 |
Viral infections of the central nervous system (CNS) constitute a significant proportion of infective ailments either in the form of meningitis or encephalitis, or both. Lack of in-house immune mediators as well as the presence of blood-brain barrier, confer complexity to the diagnostic efficacy of a given test. Not only does an accurate (and/or rapid) diagnosis help in establishing the etiology of the viral infection, it also provides an epidemiological overview of such infections in the given region. Compared to other parts of the world, most data in India gets generated from the tertiary-care or referral units and epidemiological studies/survey are scant.
To determine the etiology and epidemiology of viral infections of the CNS, Tiwari, et al.,[1] evaluated 150 cerebrospinal fluid (CSF) and 50 blood samples of patients suspected of having a viral etiology, belonging to the central part of India. They utilised quantitative real-time polymerase chain reaction (PCR), both one-step and two-step, to determine the causative agent viz. cytomegalovirus (CMV), Epstein-Barr virus (EBV), varicella-zoster virus (VZV), Japanese encephalitis virus (JEV), dengue virus, West Nile virus (WNV), and Chandipura virus. It was demonstrated that the diagnostic yield of the estimation was a meagre 14% (21/150), with VZV and JEV contributing to more than 2/3rd of positive results. The authors highlight that the PCR-positive group of patients had more severe disease and that it was advantageous to use plasmids over gDNA. They assert the utility of the SYBR green-based real-time PCR assay developed during the conduct of the present study.
Though results of the analysis highlight that 86% of samples went undetected, this may not be true in its entirety because of several reasons. Firstly, it must be explored whether the battery of investigations was comprehensive? Considering the worldwide epidemiological spectrum, the largest contributors to manifest as well as non-manifest CNS viral infection, herpes virus group and enteroviruses were not included in the estimation. Thus, for the given set of PCR performed it may in fact not be dismal.
Secondly, it is important to acknowledge that the group of neurotropic viruses is large and diagnostic strategies cannot be generalised. If we look at the applicability of the molecular tests, the most suited group of viruses are herpes virus and enteroviruses where the CSF-PCR is the diagnostic modality of choice. However, for JEV, VZV and WNV looking at the immune responses in the CSF as well as the serum will be complementary to PCR and increase the diagnostic yield of the test. It may be an altogether different scenario while estimating, as well as interpreting, an EBV infection. A serology might be more helpful in acute infection while a CSF-PCR in cases with a reactivation. Of note, a positive test for EBV might suggest an EBV infection per se or a secondary viral reactivation; thus caution needs to be exercised in diagnostic labelling. A similar situation might arise in patients suspected of having rabies where the choice of sample, CSF versus saliva versus biopsy, and the type of test, PCR versus antibodies, might be critical.[2]
Finally, the phase of CNS infection during which the sampling was done is to be kept in mind. The mere performance of a test does not guarantee a logical outcome and the test may be falsely negative. Ideally, antigen and nucleic-acid based tests should precede or at least be concurrent with the estimation of immune responses for the best yield.
Assessments by PCR have revolutionised the molecular diagnosis relevant to several infections but in order to have an in-depth analysis probably a metagenomic next-generation sequencing, with good DNA/RNA co-extraction methods, would be more appropriate in an appropriate research setting.[3]
| » References | |  |
| 1. | Tiwari RI, Bhullar SS, Chandak NH, Baheti NN, Daginawala HF, Singh LR, et al. Determination of etiology and epidemiology of viral central nervous system infections by quantitative real-time polymerase chain reaction in central India. Neurol India 2020;68:1323-30.  [Full text] |
| 2. | He T, Kaplan S, Kamboj M, Tang YW. Laboratory Diagnosis of Central Nervous System Infection. Curr Infect Dis Rep 2016;18:35. |
| 3. | Xing XW, Zhang JT, Ma YB, He MW, Yao GE, Wang W, et al. Metagenomic Next-Generation Sequencing for Diagnosis of Infectious Encephalitis and Meningitis: A Large, Prospective Case Series of 213 Patients. Front Cell Infect Microbiol 2020;10:88. |
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