Genetic variation of varicella-zoster virus: evidence for geographical separation of strains

Heteroduplex mobility assay was used to identify variants of varicella-zoster virus (VZV) circulating in the United Kingdom and elsewhere. Forty variable positions were identified. Sixteen substitutions were non-synonymous, resulting in an amino acid change, the majority of which were clustered within surface expressed proteins. Phylogenetic analysis distinguished at least three major clades (strains A, B, C) supported by significant bootstrap values. Apart from the United Kingdom and Brazil where all three strains were found, genotypes appeared to be closely associated with the geographical region in which they were sampled. Allelic co-segregation of widely spaced single nucleotide polymorphisms (SNPs) confirmed the genetic stability of the VZV. Recombination rates were difficult to calculate because of the low intra genotypic variation. However, one haplotype originating from Brazil is most parsimoniously explained as a recombinant between A and C strains, which co-occur in the region. Two further UK strains appeared to be recombinants between groups B and C.

Investigation of varicella-zoster virus variation by heteroduplex mobility assay

Heteroduplex mobility assays of 37 regions were performed on ten UK isolates of varicella zoster virus, four from cases of zoster, and six from cases of chickenpox. The variation between isolates was found to be 0.061%, which is at least five times lower than any other member of the human herpesvirus family. Fifteen of the 37 regions tested had 29 single nucleotide polymorphisms, and over half the polymorphisms were located in four gene fragments. Of the 29 SNPs, eleven were non-synonymous and these were clustered in six genes. Isolates from a child and her mother to whom she had transmitted the virus, were identical at every locus tested. All other viruses could be distinguished by a combination of SNPs and length polymorphisms of the repeat regions R1, R2 and R5.

CMV viral load measurements in whole blood and plasma--which is best following renal transplantation?

BACKGROUND

Quantitative commercial assays for cytomegalovirus (CMV) detection have recently been developed. Their role in the management of patients after transplantation needs to be evaluated. Widespread use of these assays will allow for comparison of results between centers and meaningful interpretation of the significance of viral load measurements.

METHODS

Sequential samples from 52 patients after renal transplantation were tested in the murex hybrid capture assay (HCA) and the Roche Amplicor CMV DNA assay (QPCR) and correlated with the development of CMV disease. A comparison of viral loads in plasma and whole blood was also made.

RESULTS

Both assays were sensitive and detected all cases of CMV disease. The specificity and positive predictive value increased from 0.34 and 0.36 to 0.85 and 0.96 for the HCA and 0.37, 0.37 to 0.72 and 0.63 for the QPCR following a receiver operator curve analysis. Higher viral loads were measured using the HCA compared to the QPCR. Response to ganciclovir was associated with a greater than 80% reduction in viral load by HCA or greater than 70% using the QPCR.

CONCLUSIONS

Both assays were highly sensitive. By using a receiver operator curve analysis a cutoff viral load can be determined which maximizes the clinical utility of these assays.

Use of molecular assays in diagnosis and monitoring of cytomegalovirus disease following renal transplantation

We compared two commercial molecular assays (the Murex Hybrid Capture CMV DNA assay [HCA], version 2, and the Roche Amplicor plasma PCR assay) with a standard shell vial assay in detecting and predicting cytomegalovirus (CMV) disease in a group of renal transplant patients and assessed the role of viral load measurements (using the HCA) in their management. The sensitivity of the HCA and Amplicor assay in terms of disease detection was 100%, compared to 71% for the shell vial assay. Both the HCA and the PCR assay detected all cases of disease, at medians of 11 and 12.5 days before the onset of symptoms, respectively. Significantly higher viral loads were detected in those patients with symptoms (7.9 x 10(5) copies/ml) than in patients without symptoms (7.9 x 10(4) copies/ml; P < 0.0001). There was also a trend towards higher viral loads in those patients with primary infections (7.8 x 10(5) copies/ml) than in those patients with reactivations of CMV disease or reinfections. Successful treatment with ganciclovir was associated with a >90% reduction in viral load. Both of these new assays are sensitive and easy to use. A comparison of accurate quantitation is also useful in monitoring responses to antiviral therapy.