The molecular epidemiology of herpes simplex viruses

Geographical distribution of the herpes simplex virus type 1 BgKL variant in Japan suggests gradual dispersion of the virus from Shikoku Island to the other Islands

Restriction endonuclease fragment length polymorphism (RFLP) is useful for the epidemiological study of herpes simplex virus type 1 (HSV-1). We report here the identification of a major BglII RFLP variant of HSV-1, designated BgKL, found in 27.0% of 636 HSV-1 clinical isolates. We have also established its geographic distribution in Japan. BgKL has an unusually large BglII K fragment. SalI cleavage analyses showed that 97% of BgKL variant isolates lack both the SalI C-J and the F-J cleavage sites and have an unusually large SalI D or E fragment, and 91% of the BgKL variants lack both SalI G and H fragments. Furthermore, 96% of BgKL isolates have an unusually small KpnI M fragment. Therefore, BgKL is a marker for these five mutations in most HSV-1 isolates and is a useful HSV-1 RFLP marker. The BgKL variant was found in 59% of HSV-1 isolates from Shikoku Island, 44% of HSV-1 isolates from the Chugoku region of Honshu Island, 31% of HSV-1 isolates from Kyushu Island, 0% of HSV-1 isolates from Okinawa Island, 49% of HSV-1 isolates from Osaka, 27% of HSV-1 isolates from Shiga, 13% of HSV-1 isolates from the Chubu Region, and 9% of HSV-1 isolates from the Tohoku Region of Honshu Island. Differences in the frequency of BgKL between the Shikoku-Chugoku-Osaka area (49%) and Kyushu, between Kyushu and Okinawa, between the Shikoku-Chugoku-Osaka area and Shiga, and between Shiga and Tohoku are all statistically significant. The BgKL frequency decreases in a geographical gradient suggest that this HSV-1 variant was dispersed from Shikoku to the surrounding regions and then to more distant regions. The BgKL frequency in Tokyo was similar to the nationwide average. These are the first data to suggest a geographic and demographic dispersion pattern of HSV-1. Implications for the epidemiology and diversification of HSV-1 are discussed.

Comparison of polymorphism of thymidine kinase gene and restriction fragment length polymorphism of genomic DNA in herpes simplex virus type 1

The polymorphism of the thymidine kinase (TK) gene of herpes simplex virus type 1 (HSV-1) was analyzed and was compared with the restriction fragment length polymorphism (RFLP) of the whole genome to evaluate the relative efficiency of the TK gene as a potential probe for identification and discrimination of HSV-1. The effectiveness of using the polymorphism of the TK gene in classifying HSV-1 strains was comparable to that of RFLP analysis of 66 sites, suggesting that TK gene sequencing may have important applications in epidemiological studies of HSV-1.

Analysis of genomic polymorphism among herpes simplex virus type 2 isolates from four areas of Japan and three other countries

Genomic polymorphism of 307 epidemiologically unrelated strains of herpes simplex virus type 2 (HSV-2) from four areas of Japan and three other countries (Korea, Sweden and the U.S.A.) was analysed by using 16 variable markers selected from 97 restriction endonuclease (RE) sites with five REs. In addition to the 16 markers, 26 rare variable RE sites were found in 307 isolates. Five and four of 16 markers (RE sites) were found to differ in the frequency of isolates with the markers between isolates from Japan and Sweden and between those from Japan and the U.S.A., respectively, suggesting that they are genomically different from each other. In this manner, 307 HSV-2 isolates from four countries could be classified into 68 different genotypes (no. of isolates/no. of genotypes = 4.5). Some isolates from one country or more than two countries at times were classified into the same genotypes, which were referred to as predominant genotypes. The most predominant genotypes for isolates from Japan, Sweden and the U.S.A. were genotypes 30, 26 (32) and 3, respectively, indicating that they are different by the country. In genotypes 1 and 6, the frequency of isolates was found to be significantly different between Japan and Sweden and between Japan and the U.S.A., respectively. Nine out of 16 markers differed in the most genomically distant isolates, each of which was obtained in Sweden and Japan. In addition, high correlation coefficients (r) in the Japanese isolates were detected in different pairs of markers from those in the Swedish isolates, suggesting that isolates from these two countries are evolutionarily distant.

Genomic variation among herpes simplex virus type 1 strains: virus DNA analysis of isolates from Saudi patients

Fifty-two clinical isolates of herpes simplex virus type 1 (HSV-1) from Saudi Arabian patients were analysed by restriction endonuclease digestion of the virus DNA using the enzymes HindIII and BamHI, followed by hybridization with 32P labelled DNA of laboratory strain F. Of the isolates, 17 were resolved into four distinct cleavage patterns with HindIII restriction enzyme. The remaining 35 strains had the same cleavage pattern as the standard HSV-1-F. Further investigation of the 52 isolates with BamHI, which is a multicut enzyme and therefore capable of higher resolution, differentiated 47 of the 52 isolates and were assigned into nine cleavage groups. Comparing our findings with similar studies reported elsewhere suggest geographic clustering of HSV-1 strains. Fragments giving rise to the observed DNA polymorphism were mapped to the unique region of the long and short segments of the genome.

Two outbreaks of herpes simplex virus type 1 nosocomial infection among newborns

Two outbreaks of herpes simplex virus type 1 (HSV-1) infection occurred in three newborns at each of two hospitals, and two of the infants in each case died of disseminated HSV-1 infection. Restriction endonuclease profiles of HSV-1 DNAs isolated from the three in each instance were essentially identical, indicating that they were epidemiologically related. In the first instance, each of three infants born in the same hospital at intervals of approximately 2 years or 1 year was infected with HSV-1. In this case, it was suggested that periodically reactivated HSV-1 strains from hospital personnel had been transmitted to three newborns. In the second instance (infants G-36, G-37, and G-38), the radiant warmer that had been occupied by infant G-36, who was infected with HSV-1, was used for infant G-37. Infant G-38 was in another radiant warmer 2 m from the radiant warmer occupied by infant G-37. Therefore, it was suggested that the virus had possibly been transmitted via radiant warmer and by hospital personnel in the two instances.

Restriction endonuclease cleavage analysis of herpes simplex virus isolates obtained from three pairs of siblings

Cleavage of herpes simplex virus type 1-infected cell DNA with restriction endonucleases showed that profiles of paired isolates obtained from three groups of siblings were essentially identical. This finding is different from that for profiles of other paired isolates that are epidemiologically unrelated. One set of paired isolates of the three had completely identical profiles. However, two other sets of paired isolates yielded minor heterogeneity in fragments derived from the regions spanning the unique repeat junction and repeated regions of the herpes simplex virus type 1 genome. This suggests that the regions of the herpes simplex virus genome are variable during viral DNA replication. This finding also supports the hypothesis that the same variants tend to be transmitted and thereafter perpetuate within a family cluster.

Comparison of infectious JC virus DNAs cloned from human brain

We cloned JC virus DNA obtained directly from brain tissue of 10 cases of progressive multifocal leukoencephalopathy and compared DNAs by restriction endonuclease mapping. Before cloning, each DNA preparation was homogeneous with respect to restriction patterns, but with the cloned DNAs we found variability in three regions of the genome among DNAs from different cases. There was a region of hypervariability between 0.67 and 0.725 map units; no two DNAs were exactly alike in this region. We determined that the origin of DNA replication also was in this region at 0.69 +/- 0.02 map units. In 4 of the 10 DNAs examined there was a deletion of approximately 75 base pairs between 0.14 and 0.235 map units, the region presumed to contain the codons for the C-terminal ends of the structural protein Vpl and for T antigen. JC virus DNA from these same four cases had an additional HincII-HpaI site at 0.895 map units in the presumptive Vp3 and Vp2 coding regions. Overall, no two JC virus genomes were identical although all were from fatal central nervous system infections and were infectious in vitro. Our restriction patterns suggest that there are two subtypes of JC virus circulating in the population.

Risk, susceptibility and the epidemiology of proliferative neoplastic disease: descriptive vs. mechanistic approaches

Recently there has been a confusing and somewhat frustrating difference of opinion in epidemiology concerning the relative merit and utility of descriptive versus mechanistic knowledge in approaching the comprehension and control of human cancer. This distinction has both historical and evolutionary rationale; it generally being necessary to know something of WHAT is happening before one can be legitimately concerned with HOW it is happening. As outlined below, however, there is little justification for making value judgements based on this distinction, and the situation is more one in which descriptive approaches and mechanistic approaches are equally essential in the development of a systematic viewpoint, a viewpoint providing guidance to meaningful intervention.

Herpesvirus saimiri strain variability

Herpesvirus saimiri was isolated from 22 squirrel monkeys by cocultivation of peripheral lymphocytes with permissive owl monkey kidney monolayer cells. Comparison of virion DNA fragments produced from restriction endonuclease digestion was used as a sensitive measure of strain variability. Although all isolates contained similarities and common features, 19 of the 22 were readily distinguished. Three of the isolates, however, were indistinguishable and possibly were related epidemiologically. Distinct subtypes of H. saimiri were not evident by these criteria; Peruvian, Colombian, Guyanan, and Bolivian squirrel monkeys yielded isolates without characteristic features peculiar to the geographic region. Three of three colony-born squirrel monkeys that were tested yielded a strain of virus distinct from that obtained from the mother. In separate experiments, two of three animals chosen at random yielded a strain of virus different from that originally obtained 16 and 22 months previously; only one of the three animals examined yielded the same strain of virus 22 months after the original isolation. The degree of restriction endonuclease fragment variability among H. saimiri strains appeared to be greater than previously observed for other herpesviruses.

Molecular epidemiology of cytomegalovirus infections in women and their infants

We studied cytomegaloviruses (CMV's) isolated from mothers and their children to determine whether recurrent infections and transmission to the fetus in immune women are due to reinfection or reactivaton of endogenous virus. Twenty-one strains of CMV from six mother-baby pairs, from two congenitally infected siblings, and from repeat isolates from four women were examined for genetic relatedness, by means of restriction endonuclease analysis of purified viral DNA. Although CMV's from unrelated persons were always different, strains from five to six congenitally infected babies were identical or very closely related to those from their mothers. Strains from congenitally infected siblings were also concordant, as were repeat isolates form three of four women. Major differences in viral DNA were detected in strains recovered from the same woman or from a mother-baby pair in only two cases. Endogenous CMV appears to be most frequent source of recurrent infection and intrauterine transmission in immune women; reinfection also occurs, but less commonly.