A systematic review of Human T-cell Lymphotropic Virus type-1 (HTLV-1) seroprevalence worldwide and an update on HTLV-1 diagnoses and associated diseases in England and Wales.

BackgroundHuman T-cell lymphotropic virus type-1 (HTLV-1) is a retrovirus, mainly transmitted sexually, which causes adult T-cell leukaemia/lymphoma (ATLL) and HTLV-1 associated myelopathy (HAM). We aimed to update global HTLV-1 seroprevalence estimates, estimate the number of people living with HTLV-1 (PLHTLV) in England and Wales (E&W), and present E&W HTLV-1 surveillance data.MethodWe systematically reviewed countries with new HTLV-1 prevalence data since the 2015 European Centres for Disease Control report, including studies of adults in the general population, pregnant women and blood donors (Ovid MEDLINE, 01/09/2014-17/02/2023). Global seroprevalence and UK census data were used to estimate the number of PLHTLV in E&W for 1991 and 2021. Reference laboratory and hospital data were combined to describe patterns in new HTLV-1 diagnoses, and associated diseases, in 2013-2022, in E&W. Diagnoses in 2013-2022 were compared with 1993-1997 using Incidence Rate Ratios (IRR).ResultsNew seroprevalence data were found for Pakistan (0.19%, blood donors), Malawi (0.96%, healthy mothers), Jordan (0.00%, blood donors), Vietnam (0.00%, blood donors) and New Caledonia (0.60%, general population); 4/5 studies had a high risk of bias. Among 749 newly-diagnosed PLHTLV in E&W (2013-2022), most were women (58%, 434/749) and tested in London (64%, 480/749). Where recorded, Black Caribbean ethnicity predominated (61%, 228/373); 51% (396/619) were symptomatic, most commonly with ATLL (47%, 187/396). Comparing 1993-1997 with 2013-2022, the IRR was 1.26 (95%CI 1.09-1.46) overall, 1.60 (95%CI 1.17-2.23) for ATLL and 0.35 (95%CI 0.23-0.51) for HAM. Assuming all cases were due to migration from endemic countries, the estimated number of PLHTLV in E&W increased from 11,654 (range 3,804-19,504) in 1991 to 28,846 (range 10,365-47,328) in 2021.ConclusionsIn E&W, rising annual ATLL diagnoses are consistent with an increase in the estimate of the number of PLHTLV, necessitating enhanced public health interventions. The reduced IRR for HAM requires further investigation.