Extracts from the WHO HTLV-1 Key Facts Document 3-2021

The World Health Organization WHO just released a Key Facts document on HTLV-1 infection (references below) as follow up to their February, 2020 Technical Report.  Here are some highlights for blood bankers:

HTLV-1 is efficiently transmitted by blood transfusion with a rate of 28-63% from a donor with HTLV-1 and up to 87% from a tissue transplant. 

Testing can be made more complicated due to the length of time between contracting the virus andthe seroconversion required for the virus to appear on tests. This period has been reported to be aslong as 65 days.

Mandatory HTLV-1 antibody screening of all blood donations has been implemented in 23 countries.

Because HTLV-1 is almost always cell associated, leukoreduction may be as effective as blood donation screening in preventing transmission.

Following current practices, screening tests for HTLV-1 should be followed by confirmatory tests for the diagnosis of HTLV-1.  Most screening tests use immunoassays, which rely on detecting anti-HTLV-1 antibodies. Commonly used confirmatory tests detect antibody responses to specific HTLV-1antigens.  Test types include the Western Blot, radioimmunoprecipitation assay (RIA) and linear immunoblot assay LIA.  However, the Western Blot test has been found to give unreliable results.  Several  studies have proposed transitioning from using Western Blot for confirmation in routine testing to using line immunoassay or NAT.

In my laboratory in Qatar, we detected approximately 8-10 cases of infection per year on a donor testing base of 36,000 for the year 2019.  These were confirmed cases by LIA.  In addition to the universal leukodepletion of all components to the CE-mandated level of < 1E6, we also pathogen-inactivated platelet components and plasma.


  1. Technical Report Human T-Lymphotrophic Virus Type 1, WHO, February 2020
  2. Key Facts Human T-Lymphotrophic Virus Type 1, WHO, 3/3/21