Seroepidemiology and Molecular Epidemiology of Kaposi's Sarcoma-Associated Herpesvirus Among Jewish Population Groups in Israel

Batya Davidovici, Isabella Karakis, Dimitra Bourboulia, Samuel Ariad, Jian-Chao Zong, Daniel Benharroch, Nicolas Dupin, Robin Weiss, Gary Hayward, Batia Sarov, Chris Boshoff

Affiliations of authors: B. Davidovici, I. Karakis, B. Sarov (Epidemiology Department), S. Ariad (Oncology Department), D. Benharroch (Pathology Department), Soroka University Medical Center, Ben Gurion University of the Negev, Beer-Sheva, Israel; D. Bourboulia, N. Dupin, R. Weiss, C. Boshoff, The Cancer Research Campaign (CRC) Viral Oncology Group, Departments of Oncology and Molecular Pathology, University College London, U.K.; J.-C. Zong, G. Hayward, Department of Pharmacology and Molecular Sciences, The Johns Hopkins School of Medicine, Baltimore, MD.

Correspondence to: Batia Sarov, Ph.D., M.P.H., Department of Epidemiology, Faculty of Health Sciences, Ben Gurion University, Beer Sheva, Israel (e-mail: sbatia{at}bgumail.bgu.ac.il), or to Chris Boshoff, M.R.C.P., Ph.D., The CRC Viral Oncology Group, The Wolfson Institute for Biomedical Research, The Cruciform Building, University College London, Gower St., London WC1E 6BT, U.K (e-mail: c.boshoff{at}ucl.ac.uk). Correspondence regarding molecular variance can be addressed to Gary Hayward, Ph.D. (e-mail: ghayward{at}jhmi.edu).


    ABSTRACT
 Top
 Notes
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Background: The incidence of classic Kaposi's sarcoma among Jews in Israel is among the highest in the developed world. Kaposi's sarcoma-associated herpesvirus (KSHV or human herpesvirus 8) is causally linked to Kaposi's sarcoma. Very little is known about the prevalence of KSHV in the Middle East or about the modes of transmission in Mediterranean countries. Methods: From 1992 through 1995, sera were obtained from 1648 adults who had tested positive for hepatitis B virus (HBV) surface antigen 20 years earlier at blood donations; sera were also obtained from 2403 of their family members. All sera were tested for anti-KSHV antibodies with the use of an indirect immunofluorescence assay. To analyze the effects of various factors on the risk of KSHV infection for both the HBV-positive cohort and their families, logistic regression for cluster data and generalized estimating equations were used. All statistical tests were two-sided. Results: Among family members, the seroprevalence of antibodies against KSHV was 9.9% (95% confidence interval [CI] = 8.7% to 11.1%); among the former blood donors who had tested positive for hepatitis B, it was 22% (95% CI = 19.9% to 24.1%). Overall, the best predictor of KSHV status was the place of birth. The most important risk factors found for both husband and wife to test KSHV positive were their own places of birth and their spouse's seropositivity. For a child to test positive, the most important risk factor was maternal seropositivity. Conclusions: The crude prevalence rate of KSHV among the Jewish population in Israel is 9.9%. Important routes of KSHV transmission in the families studied are spouse to spouse and mother to child. The presence of KSHV in Jews in Israel of all ethnic origins and their high incidence of reported Kaposi's sarcoma suggest that KSHV was introduced into the Jewish population prior to the major Diaspora.



    INTRODUCTION
 Top
 Notes
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
The Diaspora of the Jewish people started more than 2500 years ago. Various genetic diseases appear to cluster predominantly in either Ashkenazi Jews (from Eastern and Northwestern Europe) or Sephardi Jews (from North Africa and the Mediterranean) (1,2). The genetic mutations leading to these diseases must have been introduced after the two main arms of the Diaspora separated.

Classic Kaposi's sarcoma (KS) is relatively common in both Sephardi and Ashkenazi Jews in Israel, and the incidence of classic KS in Israel is among the highest in the developed world (37). North African Jews (Sephardi) have a higher incidence of classic KS than Jews born in Israel or in Europe (7,8). For example, compared with Jews born in Israel, the relative risk (RR) of classic KS in Sephardi Jews from Morocco, Algeria, and Tunisia is 2.01 (95% confidence interval [CI] = 1.52 to 2.65); in Ashkenazi Jews from Central Europe, the RR is 0.45 (95% CI = 0.30 to 0.66) (7,8). Despite the Diaspora, which brought the dispersal of the Jewish people worldwide, various diseases, including classic KS, appear to cluster in both Ashkenazi and Sephardi Jews. These observations suggest that the agent or genetic events responsible for KS were introduced before the Diaspora.

KS-associated herpesvirus (KSHV), also called human herpesvirus 8, is the infectious cause of KS (9,10). The seroprevalence of the virus appears to be higher in populations with, or at risk of developing, acquired immunodeficiency syndrome (AIDS)-associated KS or classic KS (1113). In Africa, where KS is a common tumor in human immunodeficiency virus 1-infected individuals, KSHV infection is relatively common, and the seroprevalence increases steadily with age, starting even before puberty (1421).

In gay men, KSHV is probably transmitted during sex (12,22,23). KSHV DNA has been found in saliva, semen, and prostatic fluid (2427). In countries where classic KS is found, very little is known about the mode(s) of transmission and the risk factors associated with transmission of KSHV.

The prevalence of KSHV in Israel and in other Middle Eastern countries is unknown. The objectives of this study were as follows: 1) to determine the prevalence of KSHV in the Jewish population of Israel, 2) to analyze the association between the prevalence rate of KSHV and population characteristics as well as hepatitis B virus (HBV) serostatus, 3) to investigate KSHV intrafamilial transmission, and 4) to determine what KSHV strains are present in Jewish patients with KS.


    SUBJECTS AND METHODS
 Top
 Notes
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Study Populations for Serologic Study

Data from two large studies conducted by the Department of Epidemiology at Ben Gurion University, Beer Sheva, Israel, are included in this article. The serum samples were collected from study clinics in 16 cities and rural locations across central and southern Israel. This study was approved by the local and national ethics committees, and the subjects gave written informed consent.

Former blood donors. An historic cohort of 1648 healthy blood donors, determined to be positive for HBV surface antigen (HBsAg) by counterimmunoelectrophoresis (28) during the period from 1971 through 1975 during their army service, was recontacted and tested for HBV markers of infection during the period from 1992 through 1995 with the use of commercial enzyme-linked immunosorbent assays (Abbott Laboratories, Chicago IL). The actual sera of 1971–1975 were not available. Of the 1648 historic blood donors retested between 1992 and 1995, 1074 (65%) remained HBsAg positive, 376 (23%) were found to have antibodies to HBV (anti-HBs and anti-HBc), and 198 (12%) were negative for all markers of HBV infection. All participants in the study clinics were interviewed and underwent a physical examination by an hepatologist. Questions were asked about sociodemographic and behavioral characteristics, including age, sex, birthplace, residence history, years of education, occupation, reproductive history, previous blood transfusions, surgery, intravenous drug use, alcohol and smoking history, and morbidity related to viral hepatitis infections.

Family members. During 1992 through 1995, a total of 2403 family members (807 spouses and 1596 children) of the 1648 HBsAg-positive blood donors described above were also invited to the study clinics. The children included were all older than 2 years. These family members underwent an interview similar to that administered to the former blood donors. In total, between the former blood donors and their family members, there were 831 nuclear families with sizes varying from two to six members (Fig. 1Go). Of these 831 nuclear families, 202 were without children, and 559 included two spouses and at least one child. Seventy families with a single parent were excluded from the analysis of intrafamilial transmission of KSHV.



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Fig. 1. Diagram of the study population.

 
Serologic Test for KSHV

All serum samples taken from the two study groups in 1995 were stored at -20 °C and shipped on dry ice to the U.K. in 1998 for anti-KSHV antibody testing. One observer, who was unaware of each subject's personal characteristics and other test results, performed all serologic assays. The KSHV-positive, Epstein-Barr virus (EBV)-negative cell line BCP1 was used for an indirect immunofluorescence assay (IFA) to detect immunoglobulin G antibodies against the KSHV latent nuclear antigen-1 (29,30). Similar or identical assays have been used previously to report on the seroprevalence of KSHV (1113,17,18,29,3133). IFA was performed as we described previously (17). The KSHV-negative cell lines Raji and Daudi were used as controls.

Serum samples found to be positive for anti-KSHV antibodies at a dilution of 1 : 100 with the use of the IFA test were scored by UV microscopy into one of the following three grades according to the intensity of the fluorescent signal: +, ++, or +++. It was shown previously that this fluorescent signal intensity score correlates with the anti-KSHV antibody titer (17) and is, therefore, useful to determine the association of anti-KSHV antibody titer with various risk factors in large studies. To confirm that the fluorescent signal intensity correlated with antibody titer in this particular study, we selected 150 serum samples (50 scored as +, 50 scored as ++, and 50 scored as +++) for retesting at doubling dilutions, starting at 1 : 100 (13). The fluorescent signal intensity score was associated with antibody titer: The median titers were 1 : 200 for signal intensity +, 1 : 3200 for signal intensity ++, and 1 : 12 800 for signal intensity +++ (P<.0001).

Statistical Analysis

A total of 4051 serum samples, comprising 1648 former blood donors and 2403 of their family members, were analyzed. Since 88% of the former blood donors tested positive for at least one marker of HBV infection, they were considered to be a highly selected population. Among the family members, the prevalence of the HBsAg marker was 1.6%, which is similar to the observed rate in the Jewish population in Israel (2%) (Sarov B, Karakis I: unpublished observation). Therefore, the KSHV prevalence was analyzed separately for the two groups.

Standardization for both age and place of birth was performed by the direct method. The reference population used was the Israeli population (by 15-year age intervals) according to the Statistical Abstracts of Israel 1996 (34). Fig. 2Go, A, shows KS incidence standardized according to the age distribution of the world population (35). To allow the comparison of our observations with the KS incidence, we estimated the age-adjusted KSHV prevalence according to the same standard population (Fig. 2Go, C) (7).



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Fig. 2. A) Adjusted Kaposi's sarcoma rates among the Jewish population in Israel. This figure was adopted from data by Iscovich et al. (7). Adjustment was done for age according to place of birth; the reference population was the world standard population. B) Crude prevalence of Kaposi's sarcoma-associated herpesvirus (KSHV) positivity among the former blood donors. Because this was a selected population of hepatitis B-positive subjects, no adjustments were made. C) Crude and adjusted prevalence of KSHV positivity among the family member group. For comparability with panel A, we adjusted for age and place of birth by using the world standard population.

 
Univariate associations of various risk factors to anti-KSHV positivity, such as age groups, sex, educational level, place of birth, and HBV markers of infection, were assessed by the {chi}2 test for categorical variables and by analysis of variance for continuous variables.

To assess possible indications for intrafamilial transmission (between spouses and parent to child), we analyzed the data in family clusters. Families were divided into four categories according to their spouses' KSHV serostatus: both anti-KSHV positive or both anti-KSHV negative (concordant pairs), male spouse anti-KSHV positive and female spouse anti-KSHV negative, or vice versa (discordant pairs).

The effects of various factors on the risk of acquiring KSHV infection was assessed with the use of logistic regression with a correction for the "family clusters" (spouse pairs) and with a generalized estimating equation (GEE) approach (xtgee) of STATA 6.0 software (Stata Corp., College Station, TX) for the family clusters with at least one child. We studied the transmission of KSHV among members of differently sized families (with children). Our working hypothesis was that risk of acquiring KSHV infection by a positive family member is related to the family size, taking under consideration such factors as crowding or personal hygiene. This scenario does not permit the use of regular logistic regression analysis. The GEE method provides robust estimates for the standard errors of the regression covariates in the presence of intracluster dependence and families of various sizes (36). Multivariate models were constructed separately for the analyses of the parent-to-child and between-spouse transmission. The logistic regression, with a correction for correlated data designed for the transmission between spouses, included all the families (n = 761). In this model, the spouses' own characteristics were included, and the outcome was the KSHV status of each spouse. The GEE multivariate model for the parent-to-child transmission included only families with at least one child (n = 559). The dependent variable in the parent-to-child transmission model was the KSHV status of each child. Each parent's KSHV serostatus and other characteristics were used as explanatory variables.

In addition, a refined definition for KSHV positivity was used and was based on estimated titers, graded according to the intensity of the fluorescent signal as low (+), medium (++), and high (+++) separately or low (+) versus high (++ and +++ combined). Since we had three levels on the scale of fluorescent intensity (ordinal variables), we analyzed them as categorical variables. This definition was used in the evaluation of the association between HBV and anti-KSHV and also as an explanatory variable in the model for parent-to-child transmission (described previously in the section entitled "Serologic Test for KSHV") (17).

All statistical tests were two-sided and were considered to be statistically significant at P<.05.

Subtyping KSHV Strains in Israel

To study the KSHV strains present in the different Jewish ethnic groups in Israel, we retrieved 26 paraffin-embedded biopsy specimens (one from Castleman's disease and 25 from KS) from the Department of Pathology, Soroka University Medical Center, Beer Sheva, which serves the entire Negev region. Blocks were selected to represent different Jewish ethnic groups (from Russia, Poland, Turkey, Iraq, Yemen, and North Africa). DNA was extracted from 50-µm paraffin-embedded tissue of all 26 biopsy specimens and shipped to the laboratory of Gary Hayward at The Johns Hopkins School of Medicine, Baltimore, MD, for the analysis of KSHV variance. Polymerase chain reaction (PCR) was performed to amplify the open reading frame K1 (ORF K1) of KSHV, as described previously (37). In summary, DNA was amplified by PCR, and amplicons were sequenced with the use of the primers and procedures described previously (37). Sequencing was done on a model 310 machine (Applied Biosystems, Foster City, CA). The sequence data used for the analysis of the KSHV subtypes encompassed translations of nucleotide sequences encoding amino acids from positions 36 to 240 of the total 289-codon hypervariable ORF K1 membrane-signaling protein. The alignments, dendrogram, and distance values were generated in the MacVector version 6.5.3 (Oxford Molecular Group, Ltd., Oxford, U.K.) implementation of the ClustalW program (Fig. 3Go). The biopsy specimens from 26 Jewish subjects were compared with prototype variants, selected from among KS lesions and primary effusion lymphoma (PEL) cell lines as described previously by Zong et al. (37).



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Fig. 3. Linear phylogenetic tree comparing the open reading frame K1 proteins of 23 Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) genomes present in KS lesions and a multicentric Castleman's disease sample from Israeli patients of Ashkenazi origin (one to 11 from Russia or Poland) or of Sephardi origin (12 to 26 from North Africa, Iraq, or Turkey) relative to the previously assigned prototype strains described by Zong et al. (37). Certain prototype strains are typical representatives of large subtypes and clades from sub-Saharan Africa (B1, A5), Austronesia (D1), and China/Korea (C3`). All other A and C strains are representative of genotypes found principally in Caucasian patients and distributed throughout Europe, the United States, and the Mediterranean basin. The numbers in the boxes correlate with the patient numbers in Table 4Go. Primary effusion lymphoma (PEL) cell lines previously described: BC3, BCBL1, HBL6/BC1, BCBLB, BCBLR, and BCP1 (37). KS samples previously characterized: 431K/N, TKS10, SKS2, ASM70/78, SKS1, TKS1, SKS9, OKS3, and BKS20 (37).

 

    RESULTS
 Top
 Notes
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
KSHV Seroprevalence in the Group of Family Members

The mean age ± standard deviation (SD) of 2403 subjects (807 spouses and 1596 children of the former blood donors) tested for KSHV was 23.13 years ± 14.51 years (range, 2–77 years). Sixty-three percent were females, and 37% were males. The prevalence of KSHV in this group was 9.9% (95% CI = 8.7% to 11.1%).

KSHV prevalence was associated directly with age (P = .011) (Table 1Go, A) and varied with country of birth (Table 1Go, A, and Fig. 2Go; P = .005). The age-adjusted prevalence (with the use of the general population of Israel in 1995 as standard) was 11.4% higher than the crude prevalence. When we adjusted for both age and place of birth according to the general population of Israel, the prevalence (9.8%) was comparable to the crude prevalence.


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Table 1. Prevalence of anti-Kaposi's sarcoma-associated herpesvirus antibodies*
 
KSHV Seroprevalence Among the Historic Group of Blood Donors

The mean age ± SD of the 1648 formal blood donors tested for KSHV was 45.2 years ± 7.4 years (range, 36–80 years). Since blood donors in Israel in 1972 were mainly male soldiers recruited for compulsory service in the army, males constituted 90.5% of this historic group of blood donors. The overall prevalence of KSHV in this group was 22% (95% CI = 19.9% to 24.1%). KSHV prevalence was directly associated with age (Table 1Go, B) and was statistically significantly associated with country of birth (Table 1Go, B, and Fig. 2Go; P<.0001).

Association Between Anti-KSHV Antibodies and HBV Infection

In the historic blood donor group, 88% (1450 of 1648) were found in 1995 to have HBV-positive markers of infection. The prevalence of KSHV was significantly higher (22.7%) among the currently HBV-seropositive former blood donors compared with 14.1% of those who tested HBV negative (P = .008; prevalence ratio [PR] = 1.76; 95% CI = 1.13 to 2.73). Among the 1074 HBsAg chronic carriers, 22% (n = 240) were positive for KSHV. Among the 376 subjects with anti-HBV antibodies (anti-HBs and anti-HBc), 24% (n = 89) were seropositive for KSHV. KSHV seroprevalence differed significantly among the three HBV subgroups ({chi}2 = 6.6; P = .01). Furthermore, those who still tested HBsAg positive in 1995 (therefore, chronic carriers) were most likely to have high titers (+++) of anti-KSHV antibodies (P = .002) (Table 2Go).


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Table 2. Association between anti-KSHV antibody titer and HBV serostatus at the follow-up test in 1995 in the former blood donor group*
 
Intrafamilial Transmission of KSHV

Between spouses. The 761 families that were included in the spouse-to-spouse transmission analysis were divided into two groups: the 559 families with two spouses and at least one child and the 202 couples without children (Fig. 1Go). Since no difference in the anti-KSHV seropositivity was observed between these two groups, they were analyzed together. In 34 couples (4.5%), both spouses tested KSHV positive. Among 190 discordant pairs, we found 136 KSHV-positive male spouses and 54 KSHV-positive female spouses. Overall, the association between the spouses' KSHV serostatus was found to be statistically significant (McNemar's {chi}21 = 35.39; P<.0001; PR = 2.52; 95% CI = 1.82 to 3.52).

We further analyzed the contribution of the family environment to prediction of KSHV seropositivity in the male or female spouse. The following potential predictors were included in a multivariate logistic regression model with a correction for the family clusters: age, place of birth, educational level (high school versus higher education [referent group]), HBV markers of infection (HBV positive versus HBV negative), and the spouse's KSHV serostatus. Only the male's place of birth (North African origin versus others) (PR = 2.26; 95% CI = 1.4 to 3.66) and his spouse's KSHV seropositivity (PR = 2.09; 95% CI = 1.19 to 3.67) were found to be associated with the male's KSHV. Variables associated with the female's KSHV serostatus were her place of birth (Europe and the Americas versus others: PR = 0.326; 95% CI = 0.106 to 1.00) and her male spouse's KSHV serostatus (PR = 2.364; 95% CI = 1.37 to 4.06).

Parent-to-child transmission. To study the possibility of parent-to-child transmission of KSHV, we investigated the 559 families with at least one child (Table 3Go).


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Table 3. Association between parental Kaposi's sarcoma-associated herpesvirus (KSHV) serostatus and the KSHV serostatus of their children in 559 Israeli Jewish families*
 
KSHV prevalence was higher among fathers (22.4%) than among mothers (11.8%) (P<.0001). Pairs of parents fell into categories of concordant or discordant KSHV status as follows: both father and mother KSHV positive (n = 24), only the mother KSHV positive (n = 42), only the father KSHV positive (n = 101), or both parents KSHV negative (n = 392) (Table 3Go). By univariate analysis, KSHV positivity among children was more likely when at least one of the parents was positive compared with neither (P<.0001).

To investigate an association between children and parents, in family clusters of different sizes, we used the GEE (xtgee) method. The most important predictor of a child's testing KSHV positive was maternal seropositivity referring to each parent's KSHV serostatus individually (P = .004). Other predictors that were statistically significantly associated with a child's KSHV seropositivity were maternal high anti-KSHV antibody titer (defined as ++ or +++ versus +) (P = .019) and years of maternal education (P = .008). If the mother tested KSHV positive, her ethnic origin (place of birth) did not contribute independently to the child's risk of testing KSHV seropositive.

KSHV Variation in KS Biopsy Specimens

The characteristics and KSHV subtypes of the 26 biopsy specimens tested for KSHV variation are summarized in Table 4Go. The KSHV K1 sequences were grouped into subtypes and clades as described previously (37,38). Fig. 3Go shows a phylogenetic tree from 23 of the 26 KS DNA samples amplified. Case numbers 2, 14, and 18 in Table 4Go are not represented in Fig. 3Go. Although these three cases clearly belong to the subtypes stated in Table 4Go, their sequence data were incomplete to be included in the phylogenetic tree analysis (Fig. 3Go).


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Table 4. Characteristics of Kaposi's sarcoma biopsy specimens tested for Kaposi's sarcoma-associated herpesvirus (KSHV) strain variation in Israel
 

    DISCUSSION
 Top
 Notes
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
We have shown here that the prevalence rate of anti-KSHV antibodies in this large group (n = 2403) of healthy Jewish subjects in Israel is 9.9% (95% CI = 8.7% to 11.1%). Although this group was initially recruited to the study as family members of former HBV-infected blood donors, they have a similar prevalence of markers of HBV infection and a similar proportional age distribution to the general Jewish population of Israel [(39,40); Sarov B, Karakis I: unpublished observation]. We, therefore, consider the 9.9% prevalence of KSHV detected in this group to be a satisfactory estimate of that in the Israeli Jewish population.

IFAs have been used widely to measure antibody responses in human sera against KSHV latent nuclear antigen-1 (LNA-1) (17,18,29,31,32). LNA-1 is the major immunogenic latent protein (41,42) in human sera, and the LNA-1 IFA used here is considered to be adequately sensitive and specific for large seroepidemiologic studies.

The prevalence rates of KSHV vary greatly in different regions of the world beyond the expected contribution of the variability that might be explained by the use of different serologic methods (31,43). The prevalence of KSHV infection in the general population in Mediterranean countries is intermediate (12% in Greece and 14% in Italy); in contrast, the KSHV prevalence in the general population is 1%–4% in Western countries (the United States and the U.K.) and in the Far East and more than 50% in central, eastern, and southern Africa (13,14,16,17,21, 29,31,33,44). The estimated prevalence rate of 10% found in our population is similar to rates observed in other Mediterranean countries. Despite the fact that the Jewish population in Israel is composed of immigrants from more than 100 countries, the crude estimated prevalence and specific prevalence estimates for different ethnic groups remained in the range of Mediterranean countries. These findings are consistent with the high incidence rate of classic KS in Israel and the relatively high incidence of both classic and iatrogenic (specifically, transplant-related) KS in people of Jewish ancestry all over the world (5,6).

In both groups studied, the seroprevalence of KSHV increased with age. This finding indicates that horizontal routes of transmission probably occur throughout life. In African populations where KSHV is endemic, viral acquisition often occurs before puberty (14,16,17,21), and the risk of KSHV infection also increases with age (17). In contrast, in North America, KSHV infection is very uncommon before adolescence (45).

Of all the potential risk factors studied by the univariate analysis in the group representing the Jewish population in Israel, the prevalence of KSHV was associated most strongly with place of birth (P = .005) (Fig. 2Go). The highest rates of anti-KSHV antibodies were found in those born in North Africa, and the lowest rates were found in those born in Europe or North America. This observation is in agreement with the particularly high incidence of KS observed among the North African Jewish immigrants in Israel (7) (Table 1Go, A and B; Fig. 2Go).

In Israel, the best measure of socioeconomic status is years of schooling. The blood donor population group was compared with the general population in Israel, and their educational level was not found to be different from the average educational level reported in Israel. Therefore, this group does not represent one of low socioeconomic status. The seroprevalence rate of KSHV in this subgroup was 22% (95% CI = 19.9% to 24.1%). The most likely explanation for the higher prevalence of KSHV in this selected blood donor group is their high HBV infection rate. One study from Uganda (14) suggested a higher detection of anti-KSHV antibodies in children with HBV infection. This finding implies that both KSHV and HBV are transmitted via similar routes in this population or that factors associated with HBV infection also favor KSHV transmission. Furthermore, we found that chronic carriers of HBV infection (HBsAg positive) were more likely to have higher anti-KSHV antibody titers as measured by fluorescent signal intensity (P = .018; Table 2Go), supporting the hypothesis of an association between these two viral infections. It could be that factors associated with HBV chronic infection facilitate re-exposure to or reactivation of KSHV, resulting in an increased anti-KSHV antibody titer, compared with HBV-negative subjects. In both study groups, there was no association between the detection of anti-KSHV antibodies and previous surgery, blood transfusions, tattoos, or intravenous drug use (data not shown).

Intrafamilial Transmission: Spouse-to-Spouse Transmission

For both males and females, the most important risk factors for testing KSHV positive were their own place of birth and their spouse's KSHV serostatus. These findings indicate that KSHV is transmitted between spouses in the Jewish population. The direct association of KSHV infection with age supports this conclusion. However, a spouse's HBV serostatus was not associated with the probability of the other spouse testing seropositive for KSHV.

Various studies [reviewed in (33,46)] have suggested that KSHV is transmitted during sex in homosexual men. Sitas et al. (17) found a statistically significant association between KSHV seropositivity and the number of heterosexual partners among black cancer patients in South Africa. To our knowledge, this is the first study to indicate that KSHV is transmitted between heterosexual married couples in a Mediterranean population with Western standards of living. The relatively low overall prevalence of KSHV indicates that horizontal transmission is probably not as efficient as that of most other herpesvirus infections.

Parent-to-Child Transmission

In this analysis, maternal KSHV seropositivity was the most important factor associated with the child's KSHV positivity (P = .004). All of the children were older than 2 years when they were first tested for KSHV; thus, transplacental (passive) transfer of maternal antibodies against KSHV was not detected. When a child was found to test positive for anti-KSHV antibodies, we can, therefore, assume that the child was exposed to the virus; i.e., the antibodies to KSHV were produced by the child's own immune system. Children were more likely to test KSHV seropositive when their mothers had a higher anti-KSHV antibody titer (defined as ++ or +++ versus +). The prevalence rate of KSHV in children was inversely associated with the mother's years of schooling (P = .008). Further analysis will determine whether sibling-to-sibling transmission of KSHV is important in this family environment, as was shown to be the case in an African population living in French Guiana (47). The HBV serostatus of the parents was not associated with the probability of their children testing KSHV positive. Paternal transmission of KSHV does not appear to be important in this population.

Molecular Variation

Nucleotide sequence analysis of the ORF K1 gene has shown that KSHV clusters into at least four major subtypes—A, B, C, and D—that have close associations with the geographic or ethnic backgrounds of infected patients (37,48). The A and C subtypes were described previously in Western AIDS and classic KS biopsy specimens. The B subtype, common in sub-Saharan Africa (37), was not seen in any biopsy specimen from Israel, indicating that the introduction of KSHV into this population was at a different time point from that when the virus spread within Africa (Table 4Go, Fig. 3Go).

Within the A and C subtypes, more than 12 distinct clades of KSHV strains were described (38). Of 15 patients of Sephardi origin from North Africa, Turkey, Yemen, and Iraq, 12 were found to belong to the C subtype (Table 4Go, Fig. 3Go). The C2 clades were described previously among Saudi Arabian iatrogenic KS and Scandinavian classic KS samples (37). The two patients from North Africa who seem to have the "wrong" virus (i.e., A1`) relative to their ethnic classification (cases 13 and 14) immigrated to Israel at relatively young ages, indicating that they might have acquired KSHV infection within Israel by contact with a Jew of non-North African origin rather than in their country of birth (Table 4Go).

A single tightly conserved cluster referred to as the A1` clade was detected in samples from seven of the 11 Russian and Polish Ashkenazi Jewish patients tested and in two of the 12 from North Africa (Table 4Go, Fig. 3Go). Infections with all of the represented clades could have been common before the Diaspora; however, those who migrated to Northern Europe may have represented a small founder group, most of whom happened to carry the A1` clade, resulting in its widespread occurrence among their descendants. Alternatively, the A1` clade may itself have evolved as a distinctive cluster relative to other A1 variants only within the past 2500 years as a consequence of familial transmission within the relatively genetically isolated population that settled in Russia and Central Europe and became the Ashkenazi branch of the Diaspora. Because classic KS is still found relatively more commonly among Jews in Eastern and Central Europe compared with the non-Jewish population (7) (Nagy K: personal communication), it is unlikely that the A1` clade was transmitted to Jews by local non-Jewish groups. However, transmission of specific KSHV clades from Ashkenazi Jews to the local non-Jewish populations might have occurred (49).

In this study, we estimated the prevalence of KSHV in Israeli Jewish population groups and identified risk factors such as age, place of birth, HBV infection, and maternal KSHV seropositivity as major predictors of KSHV positivity. We also provide clues to the specific viral subtypes and clades found in Jewish patients with KS according to their origin.


    NOTES
 
Supported by the U.K. Medical Research Council (G9825083), The Cancer Research Campaign, and Glaxo Wellcome (C. Boshoff).

We thank the following investigators for their contributions to the study: Drs. Dharam Ablashi and Harold Cooper (ABI Inc., Columbia, MD); Drs. Noya Galai, Lechaim Naggan, and Shulamith Bar-Shani (Department of Epidemiology, Ben Gurion University of the Negev); and Dr. Micha Barchana (Israel Cancer Registry, Ministry of Health, Jerusalem).


    REFERENCES
 Top
 Notes
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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Manuscript received November 4, 1999; revised November 17, 2000; accepted December 5, 2000.


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