HTLV-1 infection

HTLV-1 was the first human retrovirus discovered. It infects CD4 T cells and persists by integrating into their DNA, so infection is lifelong. The NHS England specification describes it as a chronic infection that may remain asymptomatic in most carriers but can cause serious complications in a minority. It is more common in people from or with links to endemic regions, including parts of the Caribbean, South America, sub-Saharan Africa, Japan and parts of the Middle East, and carriers are found in the UK among migrants, their children and partners.

Because the infection is often silent, many people only find out through blood donation screening, investigation of unexplained neurological symptoms, or testing of a relative or partner.

The NHS England document lists transmission by blood exposure such as transfusion or needle sharing, by sexual contact, from mother to child and through occupational exposure such as needlestick injuries. Breastfeeding is the main route of mother-to-child spread, and prolonged breastfeeding is associated with higher risk, which is why advice for carriers addresses infant feeding. UK blood services screen donations for HTLV, which has made transfusion transmission rare here.

The virus lives within cells, so it is not spread by casual contact, coughing, sharing food or hugging.

Adult T-cell leukaemia/lymphoma is an aggressive blood cancer that develops in a small proportion of carriers, typically after decades of infection and most often in those infected in infancy. HTLV-1-associated myelopathy, also called tropical spastic paraparesis, is a slowly progressive inflammation of the spinal cord causing stiff, weak legs, back pain and bladder and bowel problems; it affects a small percentage of carriers. HTLV-1 is also linked to inflammatory conditions of the eyes, skin, lungs and joints, and to strongyloides hyperinfection.

A UK cohort study from the National Centre for Human Retrovirology in London followed 296 initially symptom-free carriers between 1991 and 2024 and found that 4 developed HAM, a cumulative incidence of 1.35 per cent; all four had high viral loads at baseline, which is why viral load is monitored. Figures for lifetime risk vary between studies and populations, so a specialist can explain what is known for an individual rather than relying on a single quoted percentage.

• Adult T-cell leukaemia/lymphoma: enlarged glands, skin lesions, high calcium, abnormal white cells.

• HAM: progressive leg stiffness and weakness, urinary urgency, constipation.

• Other associations: uveitis, dermatitis, bronchiectasis and arthritis.

Diagnosis is by antibody testing with confirmatory tests, followed by measurement of the viral load in some centres. NHS England's specification notes that testing is recommended for people from endemic regions, those with unexplained neurological symptoms and sexual partners of infected people. HTLV-1 is not routinely screened in antenatal care in the UK. Referral is to an infectious diseases or specialist centre, which arranges periodic review, blood counts and neurological assessment.

Specialist HTLV clinics also address sexual health, family testing and infection control, and may link patients with support organisations.

There is no cure and no vaccine. Management focuses on monitoring for the development of disease, symptomatic treatment of complications and counselling about transmission. HAM is managed by neurology and rehabilitation teams with attention to spasticity, bladder function and mobility. ATL is treated by haematology teams with chemotherapy, antiviral combinations or other approaches depending on subtype.

The NHS England document advises that carriers inform sexual partners and use barrier contraception, and that breastfeeding is not recommended because of transmission risk through breast milk. Carriers should not donate blood, organs or tissue.

See a GP promptly for new stiffness or weakness in the legs, bladder changes, unexplained lumps, skin rashes that persist or unexplained weight loss if you know you carry HTLV-1. Call 999 for sudden weakness, loss of bladder control with back pain or collapse.