Molecular diagnosis of viral infections of the central nervous system

Routine Broad-Range Fungal Polymerase Chain Reaction With DNA Sequencing in Patients With Suspected Mycoses Does Not Add Value and Is Not Cost-Effective

Context.—

New molecular diagnostic tests regularly become available, and they may be assumed to be superior to traditional diagnostic studies. The added cost of these studies should be considered in conjunction with the value provided for patient care.

Objective.—

To assess the cost and diagnostic value of broad-range polymerase chain reaction (PCR) and DNA sequencing for the diagnosis of fungal infections compared with traditional studies.

Design.—

We reviewed the cost and clinical impact of broad-range fungal PCR/DNA sequencing for 65 specimens for which this test, a direct fungal examination, fungal culture, and a histopathologic assessment were performed.

Results.—

The sensitivity, specificity, and positive and negative predictive values for each of the assays studied were, respectively: histopathology (83.3%, 100%, 100%, and 98.3%); direct examination (66.7%, 100%, 100%, and 96.7%); fungal culture (83.3%, 100%, 100%, and 98.3%); and broad-range fungal PCR/DNA sequencing (83.3%, 95.0%, 62.5%, and 98.3%). The cost for broad-range fungal PCR/DNA sequencing was $32,500, compared with $8,591.70 for all traditional tests combined, for the 65 specimens included in this review.

Conclusions.—

Broad-range fungal PCR/DNA sequencing did not detect any infecting fungal pathogen that was not detected by at least 1 of the traditional methods, but 3 false-positives occurred. Broad-range fungal PCR/DNA sequencing is not a substitute for traditional laboratory studies and should be used judiciously to promote care affordability.

[Evaluation of an Xpert EV (Cepheid®) molecular diagnostic technique for enteroviral meningitis]

INTRODUCTION

Polymerase chain reaction (PCR) assays have shown to be useful and quick for the diagnosis of enterovirus in aseptic meningitis. The aim of our study was to analyse the changes in clinical practice after the introduction of a real-time polymerase chain reaction (RT-PCR) technique using the Xpert EV (Cepheid^®) assay for the qualitative detection of enterovirus RNA in cerebrospinal fluid specimens from children with suspected viral meningitis.

METHODS

A retrospective study was performed in children older than 1year, diagnosed with enterovirus meningitis in a third level hospital from November 2006 to February 2013. The first period, before the availability of Xpert EV (Cepheid^®) (Group1, November 2006-August 2010) was compared with the later period (Group2, September 2010-February 2013). Clinical characteristics, the mean length of stay, and the cost per inpatient cases, were compared between the 2periods.

RESULTS

Forty-one patients (60.9% male) were included, with a median age of 64 months (interquartile range 28-96). Twenty-six patients (63.4%) were included in Group2. There were non-statistically significant differences in the epidemiological, disease severity, and laboratory characteristics between both periods of study. A significant difference was observed in the mean length of stay, with it being shorter in Group2 (48hours vs 40.5hours, P=.039), and a significant lower inpatient cost per case (€779.77 vs €656.05, P<.05).

CONCLUSION

Xpert EV (Cepheid^®) assay was useful for decreasing the length of hospital stay and the costs associated with hospitalisation in children with enterovirus meningitis.

Toll-like receptors in health and disease in the brain: mechanisms and therapeutic potential

The discovery of mammalian TLRs (Toll-like receptors), first identified in 1997 based on their homology with Drosophila Toll, greatly altered our understanding of how the innate immune system recognizes and responds to diverse microbial pathogens. TLRs are evolutionarily conserved type I transmembrane proteins expressed in both immune and non-immune cells, and are typified by N-terminal leucine-rich repeats and a highly conserved C-terminal domain termed the TIR [Toll/interleukin (IL)-1 receptor] domain. Upon stimulation with their cognate ligands, TLR signalling elicits the production of cytokines, enzymes and other inflammatory mediators that can have an impact on several aspects of CNS (central nervous system) homoeostasis and pathology. For example, TLR signalling plays a crucial role in initiating host defence responses during CNS microbial infection. Furthermore, TLRs are targets for many adjuvants which help shape pathogen-specific adaptive immune responses in addition to triggering innate immunity. Our knowledge of TLR expression and function in the CNS has greatly expanded over the last decade, with new data revealing that TLRs also have an impact on non-infectious CNS diseases/injury. In particular, TLRs recognize a number of endogenous molecules liberated from damaged tissues and, as such, influence inflammatory responses during tissue injury and autoimmunity. In addition, recent studies have implicated TLR involvement during neurogenesis, and learning and memory in the absence of any underlying infectious aetiology. Owing to their presence and immune-regulatory role within the brain, TLRs represent an attractive therapeutic target for numerous CNS disorders and infectious diseases. However, it is clear that TLRs can exert either beneficial or detrimental effects in the CNS, which probably depend on the context of tissue homoeostasis or pathology. Therefore any potential therapeutic manipulation of TLRs will require an understanding of the signals governing specific CNS disorders to achieve tailored therapy.

Diagnostic strategy used to establish etiologies of encephalitis in a prospective cohort of patients in England

The laboratory diagnostic strategy used to determine the etiology of encephalitis in 203 patients is reported. An etiological diagnosis was made by first-line laboratory testing for 111 (55%) patients. Subsequent testing, based on individual case reviews, resulted in 17 (8%) further diagnoses, of which 12 (71%) were immune-mediated and 5 (29%) were due to infection. Seventy-five cases were of unknown etiology. Sixteen (8%) of 203 samples were found to be associated with either N-methyl-d-aspartate receptor or voltage-gated potassium channel complex antibodies. The most common viral causes identified were herpes simplex virus (HSV) (19%) and varicella-zoster virus (5%), while the most important bacterial cause was Mycobacterium tuberculosis (5%). The diagnostic value of testing cerebrospinal fluid (CSF) for antibody was assessed using 139 samples from 99 patients, and antibody was detected in 46 samples from 37 patients. Samples collected at 14 to 28 days were more likely to be positive than samples taken 0 to 6 days postadmission. Three PCR-negative HSV cases were diagnosed by the presence of virus-specific antibody in the central nervous system (CNS). It was not possible to make an etiological diagnosis for one-third of the cases; these were therefore considered to be due to unknown causes. Delayed sampling did not contribute to these cases. Twenty percent of the patients with infections with an unknown etiology showed evidence of localized immune activation within the CNS, but no novel viral DNA or RNA sequences were found. We conclude that a good standard of clinical investigation and thorough first-line laboratory testing allows the diagnosis of most cases of infectious encephalitis; testing for CSF antibodies allows further cases to be diagnosed. It is important that testing for immune-mediated causes also be included in a diagnostic algorithm.

A dual reporter cell assay for identifying serotype and drug susceptibility of herpes simplex virus

A dual reporter cell assay (DRCA) that allows real-time detection of herpes simplex virus (HSV) infection was developed. This was achieved by stable transfection of cells with an expression cassette that contains the dual reporter genes, secreted alkaline phosphatase (SEAP) and enhanced green fluorescent protein (EGFP), under the control of an HSV early gene promoter. Baby hamster kidney (BHK) and Chinese hamster ovary (CHO) cell lines were used as parental cell lines because the former is permissive for both HSV serotypes, HSV-1 and HSV-2, whereas the latter is susceptible to infection only by HSV-2. The DRCA permitted differential detection of HSV-1 and HSV-2 by observation of EGFP-positive cells, as substantiated by screening a total of 35 samples. The BHK-based cell line is sensitive to a viral titer as low as a single plaque-forming unit with a robust assay window as measured by a chemiluminescent assay. Evaluations of the DRCA with representative acyclovir-sensitive and acyclovir-resistant HSV strains demonstrated that their drug susceptibilities were accurately determined by a 48-h format. In summary, this novel DRCA is a useful means for serotyping of HSV in real time as well as a rapid screening method for determining anti-HSV susceptibilities.

Why are young infants tested for herpes simplex virus?

BACKGROUND

The polymerase chain reaction (PCR)-based test to detect herpes simplex virus (HSV) genome in cerebrospinal fluid (CSF) has become the test of choice for diagnosing this infection. The utility of this test in young infants undergoing sepsis evaluations is unknown.

OBJECTIVES

We sought to identify the factors that prompted physicians to include HSV PCR in their evaluation of young infants undergoing lumbar puncture. In addition, the impact of ordering this test on patient management was assessed.

METHODS

This case-control study included infants 0 to 60 days who were evaluated by lumbar puncture at the Alfred I. duPont Hospital for Children over a 5-year period. Case patients had CSF HSV PCR ordered as part of their evaluation and control patients did not.

RESULTS

Eighty-eight case patients and 83 control patients were identified. The median patient age was 12 days and most patients (55%) were male. Both groups were similar in demographics. Herpes simplex virus infection was diagnosed by PCR in 3.4% of cases. The occurrence of a seizure (adjusted odds ratio [OR], 8.3; 95% confidence interval [CI], 1.7-41.0), the performance of CSF enteroviral PCR testing (adjusted OR, 4.7; 95% CI, 1.4-15.8), and the decision to obtain hepatic transaminases (adjusted OR, 5.6; 95% CI, 2.7-11.8) were associated with the decision to perform CSF HSV PCR testing. Use of health care resources associated with PCR testing was considerable.

DISCUSSION

The occurrence of a seizure, the performance of CSF enteroviral PCR testing, and the decision to obtain hepatic transaminases were independently associated with the decision to perform CSF HSV PCR testing. Features traditionally associated with neonatal HSV infection, such as elevated numbers of CSF white blood cells or red blood cells, did not appear to influence the decision to perform CSF HSV PCR testing. The yield of testing in this population was low. Clinicians should weigh the benefits of early diagnosis in a few patients against the consequences of excessive testing in this population.

Rapid routine detection of enterovirus RNA in cerebrospinal fluid by a one-step real-time RT-PCR assay

BACKGROUND AND OBJECTIVES

This study provides a one-step transcription/real-time (TaqMan probe) PCR assay (TM-PCR) with new consensus primer and probe sequences for generic detection of human pathogenic enteroviruses including difficult to detect ones like for instance Echovirus 30. The amplicon included parts of domain IV and V of the highly conserved internal ribosomal entry site. Generic detection was confirmed by testing a panel of 41 prototypes representing all five human enterovirus/poliovirus species.

STUDY DESIGN AND RESULTS

The 95% detection limit was found to be 100 copies per run using in vitro transcribed coxsackievirus B3 RNA. TM-PCR was compared to an in house nested-PCR assay implemented in detecting enterovirus RNA from CSF samples of patients suffering from meningitis and encephalitis. Concordant results were obtained in all samples (11 positive, 101 negative). Specificity was confirmed with laboratory strains of other neurotropic viruses, and by testing 76 CSF samples of patients with encephalomyelitis disseminata, which all gave negative results.

CONCLUSIONS

The new TM-PCR is a convincing alternative to conventional PCR protocols for the diagnosis of enterovirus meningitis. The one-step strategy limits hands on time and cross contamination risk combined with accelerated assay procedure of only 100 min.

Epidemiological study of non-polio enterovirus neurological infections in children in the region of Monastir, Tunisia

The epidemiological, virological, and clinical syndromes of 86 children younger than 13 years suspected of having neurological diseases and admitted to Fattouma Bourguiba Hospital of Monastir from January 2002 to November 2003 were analyzed. The presence of enterovirus was studied in cerebrospinal fluid (CSF) samples by reverse transcription-polymerase chain reaction (RT-PCR) and by isolation on cell culture. Sixty-one (71%) specimens were positive by RT-PCR, whereas 45 (52.3%) were detected by cell culture. Eighty percent (n = 36) of cultured enteroviruses were identified, whereas 20% were untyped. Echoviruses were isolated most frequently, with 32 cases (71.1%) in children. Echovirus 6 was the most commonly identified serotype (22.2%), followed by echovirus 13 (20%). The highest incidence on neurological infection (19.6%) occurred in children less than 6 months of age. The infected children were predominantly male (62.3%). Enteroviruses were detected in all the period of the year with the highest rate in the spring and summer months. Aseptic meningitis was the most commonly diagnosed disease (49%).

Herpes Simplex Virus Infections of the Newborn

Herpes simplex virus (HSV) infection in newborns is an important cause of death and permanent neurodevelopmental disability among young children. Neonatal HSV infections can be categorized as 1) mucocutaneous (skin-eyes-mouth), 2) disseminated, or 3) encephalitic. In addition, congenital HSV infection, a distinct clinical syndrome, accounts for approximately 5% of HSV infections identified in the neonatal period. Polymerase chain reaction greatly enhances the clinician's ability to diagnosis HSV infections, but as many as 25% of infants with neonatal HSV encephalitis have negative polymerase chain reaction studies of cerebrospinal fluid. Infants with proven or suspected HSV infections should receive acyclovir 60 mg/kg/day divided every 8 hours for 14 days if disease is restricted to the skin, eyes, or mucous membranes and for 21 days if the infant has disseminated infection or encephalitis. The benefit of long-term suppression therapy after completion of the initial treatment regimen has not been established definitively. Despite therapy with acyclovir, the best available anti-HSV drug, a substantial number of HSV-infected infants with disseminated infections or encephalitis die or have long-term neurodevelopmental sequelae.