[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other RNA viruses](https://durgical.com/en/microbiology/groups/other-rna-viruses/) › Human T-lymphotropic virus type 1

[Microbiology](https://durgical.com/en/microbiology/) · [Other RNA viruses](https://durgical.com/en/microbiology/groups/other-rna-viruses/)

# Human T-lymphotropic virus type 1

- Virus
- Enveloped
- For completeness

A retrovirus that infects T cells. Most carriers never fall ill, but it can cause leukaemia or a slow paralysis of the legs.

Updated 2026-11-01

Also called: HTLV-1, HTLV-I

## Key points

- Deltaretrovirus that infects CD4 T cells
- Tax protein: oncogenesis
- Adult T-cell leukaemia/lymphoma with hypercalcaemia and flower cells
- Tropical spastic paraparesis (myelopathy)
- Focus on Colombia's Pacific coast (Tumaco)

## At a glance

**Shape**
Spherical

**Genome**
Single-stranded, positive-sense RNA, diploid

**Envelope**
Enveloped

**Family**
Retroviridae, genus Deltaretrovirus

**Size**
About 100 nm

## Morphology

- Enveloped virus with reverse transcriptase and integrase, like HIV
- Infects mainly CD4 T cells and spreads from cell to cell

## Transmission

- Prolonged breastfeeding (the main mother-to-child route)
- Sexual contact
- Transfusion of cellular blood products and organ transplant
- Shared needles

**Reservoir:** Humans

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- The Tax protein switches on T-cell growth genes and can lead to malignant transformation
- Clonal expansion of infected cells rather than mass production of free virions
- Chronic spinal cord inflammation from infected lymphocytes and the immune response

## Diseases it causes

- HTLV-1-associated myelopathy / tropical spastic paraparesis
- Adult T-cell leukaemia/lymphoma

## Clinical picture

- Most infected people stay symptom-free for life
- Tropical spastic paraparesis: progressive leg weakness and stiffness, low back pain, neurogenic bladder and bowel
- Adult T-cell leukaemia/lymphoma: lymph nodes, hepatosplenomegaly, skin lesions, hypercalcaemia
- Others: uveitis, infective dermatitis, higher risk of severe strongyloidiasis

## Diagnosis

- Screening with an immunoassay (ELISA)
- Confirmation with Western blot, line immunoassay or proviral DNA PCR, which separates HTLV-1 from HTLV-2
- In myelopathy: CSF antibodies and spinal MRI
- In leukaemia: "flower cells" on the blood film

## Treatment

There is no effective antiviral treatment for the infection. Myelopathy is managed with corticosteroids and rehabilitation; leukaemia/lymphoma with chemotherapy, zidovudine with interferon in some subtypes, and monoclonal antibodies in specialized centres.

Drug class only; doses and regimens are set by the clinician from the current guideline.

## Prevention

- Screening of blood and organ donors
- Avoiding or shortening breastfeeding by mothers with HTLV-1 when safe alternatives exist
- Condoms and not sharing needles
- No vaccine

## In Colombia

Colombia's Pacific coast, especially Tumaco (Nariño), is a recognized HTLV-1 focus: "Pacific spastic paraparesis" was described there from 1981 and later linked to the virus. Colombia screens blood banks for HTLV.

## Memory aid

HTLV-1 takes two slow roads: stiff legs (paraparesis) or leukaemia with high calcium; Tax drives both.

## Test yourself

Think of the answer, then tap the question to see it.

## Which neurological disease does HTLV-1 cause?

HTLV-1-associated myelopathy or tropical spastic paraparesis, with progressive leg weakness and stiffness.

## Which HTLV-1 protein is linked to malignant transformation of T cells?

The Tax protein, which switches on cell growth genes.

## Which region of Colombia is a classic HTLV-1 focus?

The Pacific coast, especially Tumaco in Nariño.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/human-t-lymphotropic-virus-type-1/)

## Related

- [Human immunodeficiency virus](https://durgical.com/en/microbiology/human-immunodeficiency-virus/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Other RNA viruses](https://durgical.com/en/microbiology/groups/other-rna-viruses/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Human T-lymphotropic virus-1](https://www.who.int/news-room/fact-sheets/detail/human-t-lymphotropic-virus-type-1) (World Health Organization (WHO), 2025); [Association between lymphocytotropic virus type I (HTLV-I) infection and Pacific spastic paraparesis](https://colombiamedica.univalle.edu.co/index.php/comedica/article/view/6098) (Colombia Médica (Universidad del Valle), 1986).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/microbiology/human-t-lymphotropic-virus-type-1/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/human-t-lymphotropic-virus-type-1/