Risk factors for high anti-HHV-8 antibody titers (≥1:51,200) in black, HIV-1 negative South African cancer patients: a case control study

Human herpesvirus 8 (HHV-8, also known as Kaposi's sarcoma-associated herpesvirus) is understood to be the necessary, causal agent in the development of Kaposi's Sarcoma (KS) [1‐3]. HHV-8 has been detected in the lesions of nearly all patients with Kaposi's sarcoma [4, 5] and it predicts the development of Kaposi's sarcoma when found in the blood [3, 6].

Not all individuals infected with HHV-8 develop KS suggesting the presence of a co-factor in the development of the malignancy [7, 8]. HIV infection, other immunosuppression, male gender and older age all increase risk [9, 10]. To explain the geographical variation in KS incidence world-wide, researchers have proposed additional co-factors. In particular, researchers have suggested that infection with HHV-8 later in life, high socioeconomic status and/or exposure to substances in the water or soil may be potential co-factors increasing risk for KS in adulthood [11‐13]. High anti-HHV-8 antibody titers have been correlated with high HHV-8 viral load and increased risk for development of KS [14‐16], but risk factors other than age and length of infection for elevated titers have not been determined [17, 18]. The aim of our study was to identify risk factors for high titers to HHV-8 (≥1:51,200) as a means to better understand risk factors for Kaposi's sarcoma among HIV-seronegative, black adults in South Africa. Using a database of information on over 2000 HIV-1 negative black, South African hospitalized cancer patients, we conducted a case control study of risk factors for high titers to HHV-8 (≥1:51,200) using patients with high titers as cases and HHV-8 infected patients with low titers as controls (median titer 1:200).

The primary aim of this study was to identify risk factors for high HHV-8 titers in HIV-seronegative, black South African adults as means to identify potential co-factors in the development of Kaposi's sarcoma. Studies have found that the risk of KS is increased with increasing anti-HHV-8 titers [13, 14]. Similarly, high anti-HHV-8 titers have been correlated with high HHV-8 viral load, as it is believed that the titer of antibodies against HHV-8 reflects viral load [16]. As has been described by Sitas et al., 1999, the relationship between high anti-HHV-8 titers and KS may be similar to the relationship between EBV and African Burkitt's lymphoma [28] and nasopharyngeal cancer [29]. For these two cancers, high antibody titers correlate well with the risk of disease.

In addition to HIV infection, which dramatically increases risk for KS, which has been well described, the discrepancy between the geographical distribution of KS both prior to and with the AIDS epidemic suggests the presence of an additional co-factor in the development of this malignancy [7, 30]. As Dedicoat and Newton note, HHV-8 is common in Botswana (76–87% seroprevalence) and the Gambia (29–84% seroprevalence) but KS was rare in these areas prior to the HIV epidemic. Among the community of approximately 45,000 Ethiopian Jews in Israel, HHV-8 seroprevalence is between 39–57%, however, there has been only one case of KS documented from 1982 to 1998 [8].

We examined approximately 50 potential risk factors in relation to high anti-HHV-8 titers. In our final analysis, only those factors that were significant at the 1% level were considered in the multivariate model. Risk factors that were significant for high anti-HHV-8 titers included older age and socioeconomic variables. The associations we found between age and increased risk for high HHV-8 titers concur with results from other studies [18, 31]. In contrast with the findings of Plaincoulaine et al. 2002, however, we found no greater risk for high HHV-8 titers in males than females. Looking at a subset of our sample above age 65, we also found no greater risk for males than females with high titers being 43.9% (68/155) in men and 42.9% (54/126) in women (χ² (1df) = 0.28, p = 0.59). Other studies have found that the incidence of KS is higher in males than females in endemic areas such as sub-Saharan Africa and the Mediterranean region [10, 32, 33]. As we found no difference between males and female in risk for high anti-HHV-8 titers, to explain this discrepancy, there may be additional risk factors for the development of KS.

Increasing titers associated with increasing age may be related to the natural aging process or may be a marker for length of infection as suggested by other studies [17]. It is difficult to speculate about length of infection with this cross-sectional, prevalence data. Risk factors for high titers potentially include sexual risk factors. Although we did not find any associations between lifetime number of sexual partners and high anti-HHV-8 antibody titers, we did find an association between being separated/divorced and increased risk for high anti-HHV-8 antibody titers. Being separated or divorced could be a proxy for having more sexual partners, particularly for women, who may find themselves impoverished after divorce and in need of engaging in survival sex or sex work. Alternatively, being divorced or separated may suggest low socioeconomic status.

High HHV-8 titers were associated with variables measuring socioeconomic status. Using electricity 20 years ago was protective. Electricity was used by a fraction of the urban and rural black South African population 20 years ago and was a good marker of socioeconomic status at that time. In our study, only 11.7% (257/2191) had access to electricity 20 years ago. This contrasts with the almost universal access to electricity in urban areas of Gauteng province (the province where 76.6% (1681/2191) of the sample lives) as reported in the 1996 census [34]. Having been born in an urban area was marginally associated with increased risk (p = 0.08) as was using cheaper, non-brick building materials such as tin, mud or wood for home construction (p = 0.09). Crowding may be more of a problem in urban areas and in poorer households and could be a risk factor for high titers. Research has indicated that stressors can increase EBV antibody titers through the steady-state expression of latent herpes viruses [35, 36]; it is possible that stressors correlated with low SES may account for an increase in anti-HHV8 titers. However, high anti-HHV-8 antibody titers may also be a marker of length of infection [17] particularly as those who were living in a higher SES environment 20 years ago are protected against having high HHV-8 titers. As this study is based on prevalent HHV-8 infection, we can only hypothesize about the timing and length of infection in relation to risk for high anti-HHV-8 antibody titers.

Interestingly, an association with the consumption of maize beer was a significant risk factor for high titers. Given the association between consumption of traditionally brewed alcoholic beverages and high serum ferritin iron concentrations in black South Africans [37, 38], consumption of traditional beers may facilitate the development of Kaposi's sarcoma. It has been reported that traditional beers have high concentrations of ionized, bio-available iron (between 82.0 mg/l) as a result of being brewed and fermented in iron-clad pots [39, 40]. Ziegler et al. has reported that there may be an association between exposure to the iron-rich soils of East and Central Africa and the development of KS [12]. In a case-control study of KS in HIV positive Ugandan patients, Ziegler et al. found that those who drank home-made beer less than once a week had an OR of 2.65 95%CI (1.9–3.8) although there was no trend in risk with increased consumption [11]. Our association with maize beer, however, could be a chance finding since approximately 50 significance tests were performed. Unlike the protective association found between smoking and decreased KS risk by Goedert et al. [41], we found no association between smoking and high anti-HHV-8 antibody titers.

As this case control study was based on prevalent HHV-8 infection, it is important to emphasize the limitations of using this type of data. We were unable to establish a temporal relationship between high anti-HHV-8 antibody titers and the multitude of predictors evaluated in this study. Additionally, as some of our conclusions differ from studies that have evaluated risk factors for KS, there may be different risk factors for KS and anti-HHV-8 antibody titers that should be evaluated in future studies.

The associations we found between age, socioeconomic status and consumption of traditionally brewed alcoholic beverages and high anti-HHV-8 titers need to be examined in a prospective study. If there is an association between the development of KS and consumption of traditionally brewed beers due to the high levels of bio-available iron in these beers, public health campaigns could be directed at the replacement of iron containers with earthenware pots [42]. Additionally, specifics of the low socioeconomic environment that may increase risk for high anti-HHV-8 antibody titers such as crowding need to be examined in prospective study.

HHV-8: Human herpesvirus 8.

KS: Kaposi's sarcoma

FS conceived of the study, participated in its design, coordination and supervised the statistical analysis. JW was involved in the design of the study and performed the statistical analysis. RN was involved in the design of the study and supervised the statistical analysis. MU and LS were involved in the design of the study. MP, PR and RS supplied patients for this study. MH provided pathology reports and participated in the study design. DB performed the immunofluorescence assays. All authors read and approved the final manuscript.