|
|
||||||||
1 From the Rotterdam Eye Hospital, Rotterdam, The Netherlands; the 2 Institute of Virology, Erasmus University, Rotterdam, The Netherlands; and the 3 Medical Center Rijnmond-Zuid, Rotterdam, The Netherlands.
| Abstract |
|---|
|
|
|---|
METHODS. From 30 patients with RHK, sequential corneal HSV-1 isolates were genotyped by PCR amplification of the hypervariable regions located within the HSV-1 genes US1, US10/11, and US12. The clinical data from the patients obtained retrospectively were: ophthalmologic history, clinical picture during recurrences, number and time points of penetrating keratoplasty (PKP), and steroid or acyclovir treatment.
RESULTS. Whereas the sequential corneal HSV-1 isolates of 19 (63%) of 30 patients had the same genotype (designated as group 1), the sequential isolates of 11 patients (37%) were genetically different (designated as group 2). Among the clinical data analyzed, only the time point of PKP was significantly different between the patient groups. Although no patients in group 1 had undergone transplantation between samplings, 4 of 11 patients in group 2 underwent PKP during the inter-recurrence period in the same eye from which the corneal HSV-1 isolates were obtained.
CONCLUSIONS. The data demonstrate that RHK is frequently associated with corneal reinfection with a different HSV-1 strain and suggest that PKP is a risk factor for corneal HSV-1 superinfection.
| Introduction |
|---|
|
|
|---|
Recrudescent HSV infections are thought to result from reactivation of the HSV strain acquired during primary infection.4 5 6 However, reinfection with a new HSV strain (i.e., superinfection) at the site of primary infection has also been documented.6 7 The route or mode of HSV superinfection and its clinical consequences remain enigmatic. Genetically different HSV strains have been shown to induce different types of ocular lesions.8 Furthermore, newly acquired herpetic keratitis may develop after penetrating keratoplasty (PKP) in patients who undergo transplantation for reasons unrelated to HSV infection, suggesting the possibility of HSV-1 transmission through cornea transplantation.9 These issues underline the clinical importance of knowing whether recurrent corneal HSV-1 infections are caused by reactivation of latent virus or superinfection with a different virus strain. Molecular analyses of corneal HSV-1 isolates may allow distinction between both options.
The genome of HSV-1 consists of a unique long (UL) and a unique short (US) component, each of which is flanked by a pair of oppositely oriented repeat elements. Several hypervariable regions have been identified in the HSV-1 genome. These regions encompass unique tandemly repeated sequences, reiterations (Re) that vary in copy number and nucleotide sequences (Fig. 1) .1 10 11 Generally, two types of restriction fragment length polymorphism (RFLP) analyses are used to differentiate HSV-1 isolates. One type is the variation due mostly to a gain or loss of a restriction enzyme cleavage site. The other appears as variation in length of cleaved fragments derived from Re-containing genomic HSV-1 regions.11 Among the eight Re regions described for HSV-1, ReIV and -VIII (both located within the introns of genes US1 and US12) and ReVII (located within the protein coding region of genes US10 and US11) have been shown to remain stable during in vitro culture and have been used as sensitive and reliable markers to differentiate HSV-1 strains.12 13 14 15
|
| Materials and Methods |
|---|
|
|
|---|
Genotypic Analyses of Corneal HSV-1 Isolates
Genotypic analyses of the viral strains were performed by
amplification of the hypervariable regions within the HSV-1 genes
US1, US10/11, and US12.
This method is based on strain-to-strain differences in the number of
Re and point mutations within these hypervariable genomic
regions.10
12
13
15
DNA was extracted from the primary
corneal HSV-1 cultures, lysed in a guanidine isothiocyanate buffer
using a silica solution (Celite; Jansen Chemika, Beers,
Belgium), as described previously.15
The PCR primers
and conditions for amplifying and detecting by Southern blot analysis
of the hypervariable regions of the HSV-1 genes US1,
US10/11, and US12 have been
described.15
In case of small differences in length
between amplicons (i.e., PCR products) from individual samples, the PCR
products were run on denaturating (8 M urea) 6% acrylamide gels. The
lengths of the amplicons were estimated by comparison to a 100- and
25-bp DNA ladder (Gibco BRL, Grand Island, NY). To confirm similarities
or differences in amplicon length, all samples were finally
electrophoresed in order of increasing length.
Statistical Analyses
The statistical evaluation of the results was performed using
the Fisher exact test. Results were considered statistically
significant at P < 0.05.
| Results |
|---|
|
|
|---|
|
|
Comparison of Clinical Characteristics of Patients with RHK in
Patient Groups 1 and 2
Compared with previous reports on patients with
RHK,2
9
our cohort consisted mainly of patients with
severe entities of HSV-induced keratitis, such as herpetic stromal and
necrotizing keratitis. This is also reflected in the high number of
PKPs in the patient cohort (Table 2
; mean PKPs, 1.4 per patient; range, 06).
|
Comparison of Therapeutic Regimen for RHK in Patient Groups 1 and 2
The clinical outcome of corticosteroid treatment before or during
the convalescence period was not statistically different between both
groups. The potential effects of long-term (val)acyclovir treatment
were not numerous enough to be interpreted (data not shown).
Although the mean number of PKP per patient did not significantly differ between both groups, indicating that both groups were comparable in disease severity, a correlation between corneal HSV-1 superinfection and time point of PKP was observed. Whereas no patient in group 1 received a corneal transplant between the sampled recurrences, 4 of the 11 patients in group 2 underwent a PKP during the inter-recurrence period in the same eye from which the sequential corneal HSV-1 isolates were obtained (Table 2 ; P = 0.012). Patient 30 received a corneal allograft between the first and second sampled recurrence.
| Discussion |
|---|
|
|
|---|
Genotypic analyses of sequential corneal HSV-1 isolates from 30 patients with RHK demonstrated that 63% of the patients (patients 119; designated as group 1) had evidence of reactivation of the same HSV-1 strain. From five patients in group 1, the isolates were obtained from separate eyes. HSV-1 infection of the contralateral cornea most likely occurred through the external route (cross-infection). It was interesting that sequential isolates of 37% of the patients (patients 2030; designated as group 2) had a different genotype, suggesting corneal HSV-1 superinfection in the inter-recurrence period.
Alternatively, the instability of the analyzed hypervariable regions may account for these differences. HSVs, similar to other DNA viruses, have less genomic variability than RNA viruses and are genetically more stable after in vitro passages.11 15 In addition to standard RFLP, several hypervariable regions within the HSV-1 genome have been used to differentiate HSV-1 isolates genetically.11 Intratypic variation of the regions results from differences in the number of Re and point mutations.10 12 13 The stability of the eight HSV-1specific Re regions described varies extensively.11 Genotypic analyses of HSV-1 single-plaque clones compared with their parental strain have shown that the hypervariable regions located within the HSV-1 genes US1, US12, and US10/11 remain stable during in vitro culture.13 15 Moreover, the mean inter-recurrence period of patient group 1 (30.4 months) and the proofreading activity of Pfu DNA polymerase, implies that the intraindividual HSV-1 genotype differences are most likely not due to a genetic alteration of the initial strain or errors in amplifying these highly GC-rich DNA sequences, respectively.
Analogous to our study, reinfection with new HSV-2 strains has been described in two of three patients with recurrent HSV-2 genital herpes.7 The latter study and our data indicate that HSV superinfection is not as rare as previously suggested.4 5 6 To differentiate HSV strains, most investigators have used RFLP analyses with 6-bp recognizing restriction enzymes (REs).4 5 6 The lower efficacy of 6-bp RE, compared with the 4-bp RE, to differentiate HSV-1 strains may account for the different frequencies of HSV superinfection described.11
Generally, corneal HSV-1 infection results in the development of herpetic epithelial keratitis in approximately two thirds of patients.2 In the present study, however, the patient cohort consisted predominantly of patients with severe entities of herpetic keratitis (Table 2) . Selection of individuals with a higher susceptibility for corneal HSV-1 infection may have occurred. Alternatively, the patients in group 2 may have been superinfected with a more virulent HSV-1 strain.
Among the clinical data analyzed, only the time point of PKP was
significantly different between the patient groups. Although no
patients in group 1 had undergone transplantation between sampling, 4
of 11 patients in group 2 underwent PKP during the inter-recurrence
period in the same eye from which the corneal HSV-1 isolates were
obtained. The data suggest that PKP is a risk factor for corneal HSV-1
superinfection. Primary graft failure and endothelial abnormalities of
cultured eye bank corneas have been associated with the presence of
HSV-1 DNA in affected corneal allografts.16
The high
prevalence of HSV-1 DNA in eye bank corneas (
10%)16
has led to the hypothesis of HSV-1 latency in corneas. Although
expression of HSV-1 latency-associated transcript, a marker of latency,
has been detected in latently infected rabbit corneas and human HSK
corneas, corneal HSV-1 latency remains controversial.16
17
Recently, Zheng et al.18
have demonstrated HSV-1
transmission through PKP in an experimental rabbit model. HSV-1 DNA was
detected in recipient corneal rims and the innervating trigeminal
ganglion (TG) of naive rabbits that received corneal allografts
from latently infected rabbits. Moreover, infectious HSV-1 was
recovered from the tear film of the rabbits that had undergone
transplantation.18
Besides true ocular viral latency,
putative HSV-1 transmission through PKP may be due to coincidental
shedding of small amounts of infectious virus from the allograft or a
low level of viral replication in corneal resident cells in the
allograft at time of PKP.18
19
Alternatively, the TG may harbor a mixture of HSV-1 strains with which the patients were previously latently infected, before PKP. In animal model studies, corneal trauma (similar to PKP) has been shown to induce reactivation of HSV-1 causing corneal HSV-1 infection.20 21 Assuming that the human TG can be latently infected with multiple HSV-1 strains, PKP may serve as a powerful reactivation stimulus to certain portions of the TG, allowing multiple strains to reactivate.22
In conclusion, this study is the first to demonstrate a high frequency of corneal HSV-1 superinfection in patients with RHK. Although we could not determine the source or mode of corneal HSV-1 superinfection in patient group 2, the data suggest that PKP may be a risk factor for transmission of HSV-1 with subsequent reactivation of the donor-derived HSV-1 strain in the corneal allograft. Recently, we have genetically characterized HSV-1 DNA isolated from a donor cornea before and after PKP in a patient with newly acquired herpetic keratitis. The DNA sequences were identical in both strains, providing conclusive evidence for graft-to-host transmission of HSV-1 through corneal allograft.23
| Footnotes |
|---|
Submitted for publication May 18, 2001; revised September 24, 2001; accepted October 18, 2001.
Commercial relationships policy: N.
The publication costs of this article were defrayed in part by page
charge payment. This article must therefore be marked
"advertisement" in accordance with 18 U.S.C.
1734
solely to indicate this fact.
Corresponding author: Georges M. G. M. Verjans, Institute of Virology, Erasmus University Rotterdam, Dr. Molewaterplein 50, 3015 GE, Rotterdam, The Netherlands; verjans{at}viro.fgg.eur.nl
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
K. Umene and T. Kawana Divergence of reiterated sequences in a series of genital isolates of herpes simplex virus type 1 from individual patients J. Gen. Virol., April 1, 2003; 84(4): 917 - 923. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |