Background: Herpes virus type 8 (HHV-8) is associated with rare clinical conditions in immunosuppressed individuals, including solid organ transplant (SOT) recipients. Kaposi’s sarcoma (KS) is usually associated with reactivation of pre-existing infection, but where infection is acquired through the transplanted graft, severe disease such as visceral KS, Multicentric Castleman Disease (MCD) and Kaposi Sarcoma Inflammatory Cytokine Syndrome (KICS) can occur within months from transplantation. These remain infrequent events, but with potential to cause high morbidity in recipients who develop disease following graft-related primary infection.
Methods: Several cases of fatal and non-fatal donor-derived HHV-8 infection were investigated in the UK, leading to an independent expert safety committee review and a recommendation to commence serological screening in deceased organ donors. Post-donation testing comprises of lytic and latent indirect immunofluorescence testing in plasma; reactive samples are tested for viral DNA by polymerase chain reaction (PCR). An antibody reactive donor result triggers recipient follow up according to a national protocol, for early identification of infection and disease manifestation. Baseline serology, followed by serology and PCR at set time points allows identification of seroconversion and primary viraemia in recipients.
Results: Between May 2023-April 2025, 3021 donors were tested. In the absence of a confirmatory gold standard, serology results are expressed as reactivity rates: the overall antibody reactivity rate was 7.48%, with 4.17% being inconclusive, 1.62% low reactive and 1.62% positive; the latter is in keeping with the expected seroprevalence in our donor population. The 226 sero-reactive samples were tested by PCR, with HHV-8 DNA detectable in 9 (0.30%). 473 recipients commenced follow up, with de novo infection detected in 19; of note, all transmissions were linked to the 9 donors with detectable viral DNA. Transmission rate via kidney transplant was 47% (7/15), none developed disease to date and follow up is ongoing. Transmission rate via liver transplantation was 100% (9/9); 4 recipients remain asymptomatic and 5 developed HHV-8 related illness and died (56% mortality). 2/2 simultaneous kidney-pancreas and 1/1 bilateral lung recipients became infected and remain asymptomatic.
Discussion: Determinants of transmission via the transplanted graft, and of disease development in recipients are yet to be clearly defined. Donor screening and recipient follow up has been very challenging but awareness of HHV-8 infection in the context of SOT has been raised; multidisciplinary efforts will hopefully bring experience in monitoring and managing patients, with the aim to improve outcomes. Using the information gained through the screening program, we are currently considering strategy options to improve safety, whilst avoiding unintended negative impact on donation and transplantation.