Human T-cell lymphotropic virus-1
Human T‐cell lymphotropic virus‐1 (HTLV‐1) is the first human retrovirus to be identified. It was originally detected in 1977 from a patient with skin T‐cell lymphoma and a patient with a newly described condition, adult T‐cell leukaemia.
This retrovirus causes an aggressive malignancy of the blood and blood-forming organs, known as adult T-cell leukaemia/lymphoma (ATL). HTLV-1 also causes a progressive neurological condition known as HTLV-1-associated myelopathy or tropical spastic paraparesis (HAM/TSP). Serological studies show that infection with HTLV‐1 is endemic in some countries and rare in others, with considerable intraregional variation.
Most high-income countries have introduced HTLV-1 screening of blood donations, but few public health measures have been implemented. More concerted global public health actions are needed to contain this infectious disease.
HTLV-1 technical report and findings
In 2019, WHO organized a global meeting of stakeholders involved in HTLV-1, including leading nongovernment organization partners such as the International Retrovirology Association, and national partners such as the National Centre for Global Health and Medicine of Japan. The meeting aimed to review global and regional epidemiology, examine transmission routes of HTLV-1 infection, and identify public health approaches.
Based on studies from endemic regions It is estimated that somewhere between 5 million and 10 million people are living with HTLV-1 infection.
HTLV-1 infections are transmitted by direct contact via breastfeeding, sexual contact and blood transfusions. HTLV-1 is a lifelong infection. Mother-to-child transmission of HTLV-1 occurs primarily through breastfeeding, with limited evidence of intrauterine transmission or transmission during delivery. Acquisition of HTLV‐1 in adult life is relatively less common. Studies suggest that ATL occurs after decades of infection.
A range of tests are available for HTLV-1. Screening tests include enzyme immunoassay and the HTLV-infected cell culture-based indirect immunofluorescence assays. Confirmatory tests are polymerase chain reaction, Western blot, radioimmunoassay and line immunoassay. Pro-viral load measured by polymerase chain reaction is a useful prognostic marker used in the management of HTLV-1.
Prevention and management of clinical syndromes
Current prevention measures include cessation of breastfeeding by infected mothers and HTLV-1 antibody screening for blood transfusion.
The clinical manifestations of HTLV-1 are ATL and HAM/TSP. Other rare clinical presentations are infective dermatitis and uveitis. The median survival for people diagnosed with acute and lymphomatous ATL is less than 12 months. The median time from onset of HAM/TSP to death is 9.7 years. ATL is not curable with currently available treatment options. Antiviral therapy with interferon, in combination with zidovudine, chemotherapeutic agents and biological agents such as mogamulizumab, have shown promise in the treatment of ATL. Prednisolone is currently the mainstay of therapy for the management of HAM/TSP.
Proposed global public health response to HTLV-1
Controlling transmission of HTLV-1 infections can reduce the disease burden. HTLV-1 prevention can be integrated into blood safety, sexually transmitted infection services, and prevention of mother-to-child infection in prevalent settings.
Vaccination strategies are expected to reduce the disease burden in endemic settings. Efforts should be directed towards testing approaches and strategies for HTLV-1 detection that are appropriate to the setting and the purpose.