The HIV and AIDS epidemic has dramatically increased the frequency of different malignancies particularly Kaposi's sarcoma (KS) and certain malignant lymphoma (ML) which are associated with the novel human herpesvirus type 8 (HHV-8)/Kaposi's sarcoma-associated herpes virus (KSHV) and have become a major health concern in sub-Saharan Africa including Tanzania 123. The prevalence of HHV-8 varies from high-endemicity (30–70%) areas (sub-Saharan Africa), intermediate (5–20%) [Mediterranean] and low (≤ 5%) (Northern Europe, USA, south-east Asia and Japan) reflecting the KS and HIV epidemiology 45. HHV-8 has a high (≈50%) prevalence in the healthy Tanzanian population (blood donors) although the prevalence in Tanzanian patients with and without tumors is poorly documented 6. Seroconversion to HHV-8 precedes and therefore is predictive of KS development 4 and serodetection may also help to confirm KS diagnosis in suspect and/or borderline tumour lesions. HHV-8 transmission is known to occur both horizontally (orally, sexually and parenterally) and vertically (mother-to-child) particularly in endemic areas 78. Obviously, large-scale HHV-8 screening would be beneficial and allow preventive/therapeutic interventions including possible anti-HHV-8 vaccination in at-risk populations, but this is not yet well documented in Africa, particularly Tanzania. Previous studies on HHV-8 in Tanzania were based on polymerase chain reaction (PCR) assay which is not readily and widely available in resource-constrained developing countries 569. Furthermore, the tested non-KS Tanzanian sera in the previous study by Massambu et al., (2003) 6 were very few calling for the current larger study of hospital patients (KS, non-KS neoplasia and non-malignant clinical conditions), for comparison with our previous reports including that on healthy blood donors, which was based on immunofluorescence assay (IFA) and real-time PCR 5, The use of IFA necessitates culturing and subsequent processing of a HHV-8+ body cavity-based lymphoma (BCBL-1) cell line or another B-cell line (BCP-1) which may not be readily available and affordable in Tanzania particularly on a routine/large scale screening basis. Enzyme-linked immunoassays (ELISA) do not involve the use of cell cultures and thus provide an easy and more affordable screening method for HHV-8 infection. HHV-8 sero-detection technology is still a developing area and new assays like ELISAs may not yet have been tested in the high-endemicity African sera as compared to IFA 410. Our present study therefore, compares IFA and ELISA for HHV-8 serology of indigenous Tanzanians thus establishing an assay for possible routine use. Furthermore, although it is known that HIV transactivates HHV-8/KSHV infection mostly by its Tat protein, the association of HHV-8 and HIV with non-KS neoplasia and non-malignant (reactive) conditions in Tanzania has not yet been examined and is therefore evaluated in the present study 6.

All the three studied Tanzanian disease groups showed comparable demographical features and the male predominance in all KS types is concordant with previous findings by us and others 568. The relatively high seroprevalence for HHV-8/KSHV in patients with non-KS tumors and non-neoplastic (reactive) conditions has not been previously documented in Tanzania and is compatible with a relatively high endemic incidence of HHV-8 infection 56.

The rather high prevalence of HIV infection in two-thirds of the studied cohort patients at MNH is alarming but also reflects a KS diagnostic selection bias. The dramatic (8-fold) difference in the male:female ratio of EKS (1:27) and AKS (1:3) confirms previous reports from Tanzania, eastern Africa and elsewhere 81112131415. This sex ratio decline in AKS apparently, reflects an increased frequency of HIV infected sexually active females, compared to males of the same age group and a suggested biological gender resistance for females to non-HIV forms of KS [EKS, classic (CKS) and iatrogenic (IKS)] which clearly show a male predominance particularly in homosexuals 2811141617. The finding that most non-KS tumors in our selected cohort were HIV negative emphasizes the notion that essentially, KS today is an AIDS-defining malignancy.

As expected by their KS diagnosis, the HHV-8 seroprevalence (90%) in the studied cohort sera was higher than that in the healthy non-hospitalized population of about 50% in Tanzania 56 and of 70% in sub-Saharan Africa 4. The slightly lower seroprevalence observed in our previous PCR study could be attributed to the small KS sample size compared to that in our present study 6 but differences in assay sensitivity/specificity should also be considered 4. Obviously, this high HHV-8 frequency in patients at MNH implies a potential high risk of parenteral/iatrogenic transmission for both patients and staff, particularly during blood transfusion and other invasive procedures, as well as in intravenous (IV) drug users 4518.

The higher (93%) HHV-8 prevalence among KS cases compared to non-KS tumors and reactive lesions supports a causal relationship between the virus and primarily KS but other lymphoid tumors as primary effusion lymphoma (PEL) or body cavity-based lymphoma (BCBL) and multicentric Castleman's disease (MCD) which may also be associated with HHV-8 2519 were surprisingly not evident in our study.

Evidently, the finding that HHV-8 was more prevalent in males in all disease groups is concordant to our previous reports and others 5681120 on HHV-8 seroprevalence in KS and that KS is predominantly a male disease in cutaneous AIDS-associated (AKS), African endemic (EKS), classical (CKS) and iatrogenic [IKS]/post-transplantation Kaposi's sarcoma 681120 although, we have recently reported an increased frequency of females with oral AKS (OAKS) 8. Furthermore, we have shown previously that HHV-8 is not only more frequent in males, but that they appear to have higher viral (HHV-8) loads than females in both sera and tissue lesions by both immuhistochemistry and real-time PCR 68. Reasons for this sex differences are yet not fully clarified although various biological and socio-behavioral factors were suggested 68. Recently in a comparative genomic hybridization (CGH) and interphase-fluorescence in-situ hybridization (interphase FISH) study, we have reported cytogenetic differences between male and female KS patients including the loss of chromosome Y observed in all early and the majority of late male AKS and EKS representing a clonal genomic change 21. Moreover, in early stage disease loss of Y chromosome was the only recurrent change found 21. These features are apparently, mainly related to early male KS pathogenesis and may therefore indicate cytogenetic reasons for the sex differences in KS 21. Furthermore, the higher seroprevalence of the oncogenic HHV-8 among male KS patients may also relate to the higher frequency of KS in males 682021.

Interestingly, the male predominance for HHV-8 seroprevalence in our current study was also seen in non-KS and non-neoplastic patients suggesting a possible higher susceptibility/permissiveness of males to KSHV/HHV-8 infection and/or a high viral transmission among male homosexuals and intravenous (IV) drug users usually, mostly males 8182223. However, the association of sex with KS development and HHV-8 infection is yet to be fully elucidated.

Our finding that HHV-8 antibody seroprevalent patients at MNH were 3-times more often HIV co-prevalent than the HHV-8 seronegative cases is consistent with other reports 41824 indicating corresponding seroepidemiology for these viruses, partly explaining the much increased risk of KS development among those HIV and HHV-8 co-infected as compared to those infected with either or neither of the viruses 2481824. Furthermore, the findings support also the notion of HIV and HHV-8 cross-talk, partly achieved through the transactivation of KSHV by HIV-Tat as reported previously by us and others 26925. This HIV-HHV8 cross-talk, calls for exploration for the development and application of possible combined anti-HIV, anti-HHV-8 and anti-KS prevention and therapeutic strategies among high-risk groups including HIV-infected and AIDS patients.

The finding that IFA showed greater sensitivity than ELISA is probably due to that IFA methods shows antibodies to both lytic and latent antigens and that lytic are reportedly more sensitive 5. However, our finding that ELISA had apparently, higher positive predictive value as well as specificity and still had a high sensitivity was unexpected and particularly favourable as it makes HHV-8 screening more affordable in a resource-constrained country like Tanzania, mostly lacking the cell culture and fluorescence microscopy facilities needed in IFA. Consequently, ELISA can allow larger-scale screening of HIV high-risk groups including blood/organ donors and thereby prevent KS development through early antiviral interventions (including vaccination) 45. However, these findings are prone to observer errors, sampling bias (hospital data) including the fact that HHV-8 screening is a field that is still evolving methodologically 4. Nevertheless, the IFA method also appears to afford visual evaluation of the percentage seroprevalence of lytic as well as latent anti-HHV-8 antibodies apparently, allowing categorization of patients as being in the productive and potentially infective (lytic) and non-productive but oncogenically more significant latent phase 2 and may therefore be useful when such characterization is desired for clinical or public health interventions.

Our finding that all sera from early stage (patch-plaque) KS were positive for anti-HHV-8 antibodies while all negative sera were from LANA+ biopsies of nodular KS patients, further supports our previous notion of stage-dependent tissue-serum discrepancy in viral antigen and antibody expression probably due to virus tissue retention, immune-segregation and/or selective clearance during KS evolution 619.

Again, the clear relationship between HHV-8 and HIV infections and KS prevalence underlines the interaction between the two viruses being possibly facilitated in part, by similar transmission patterns and also, their transactivation capacity 24619.

HHV-8 seroprevalence in patients at MNH Tanzania appears to be high as expected, in HIV+ and HIV- KS cases and males but also in the HIV seronegative non-KS tumors. ELISA showed a combination of high HHV-8 sensitivity as well as higher PPV and specificity compared to IFA which however showed higher sensitivity. An apparent stage-dependent tissue-serum discrepancy in HHV-8 antigen and antibody expression seems to support the notion of immune-segregation and/or selective virus clearance during the evolution KS. HHV-8 screening of patients at risk of KS and of blood and organ donors particularly in high endemic areas will evidently help prevent development of KS.

The authors declare that they have no competing interests.