Human T-lymphotropic virus

HTLV-1 and HIV-1 EM 8241 lores

Human T-lymphotropic virus (HTLV) is a type of retrovirus that infects T cells, a type of white blood cell, in the human immune system. First identified in the early 1980s, HTLV is known to cause several diseases, including adult T-cell leukemia/lymphoma (ATL) and HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). There are four main types of HTLV, designated as HTLV-1, HTLV-2, HTLV-3, and HTLV-4, with HTLV-1 being the most pathogenic and widely studied.

Transmission

HTLV is transmitted through bodily fluids, including blood, breast milk, and semen. The primary routes of transmission are sexual contact, mother-to-child transmission (especially through breastfeeding), and blood transfusion or sharing of contaminated needles. The virus integrates into the host's DNA, making it a permanent part of the host's genetic material.

Pathogenesis

Once HTLV infects a host, it primarily targets CD4+ T lymphocytes. The virus integrates its DNA into the host cell's genome, which can lead to cellular transformation and proliferation. This process is associated with the development of ATL in a small percentage of HTLV-1 infected individuals, typically after a long latency period. HTLV-1 can also induce a chronic inflammatory response in the nervous system, leading to HAM/TSP.

Clinical Manifestations

The majority of HTLV-infected individuals remain asymptomatic carriers throughout their lives. However, a minority develop serious conditions such as ATL or HAM/TSP. ATL is characterized by aggressive cancer of the T cells, while HAM/TSP is a neurological condition that leads to progressive weakness and paralysis of the lower extremities, urinary incontinence, and muscle spasms.

Diagnosis

Diagnosis of HTLV infection is primarily based on serological testing to detect antibodies against the virus. Polymerase chain reaction (PCR) tests can also be used to identify viral DNA in the blood, providing a direct evidence of infection.

Treatment and Management

There is currently no cure for HTLV infections. Treatment focuses on managing symptoms and complications. For ATL, chemotherapy and antiviral therapy with interferon-alpha and zidovudine may be used. Management of HAM/TSP includes the use of corticosteroids to reduce inflammation and relieve symptoms.

Prevention

Preventive measures against HTLV transmission include screening blood products, promoting safe sex practices, and advising infected mothers against breastfeeding. There is currently no vaccine available for HTLV.

Epidemiology

HTLV-1 is endemic in certain parts of the world, including Japan, the Caribbean, parts of Africa, and Iran. HTLV-2 is more common among indigenous populations in the Americas and in certain groups of intravenous drug users.

Research Directions

Research on HTLV continues to focus on understanding the virus's life cycle, pathogenesis, and effects on the immune system. Efforts are also underway to develop effective treatments and a vaccine to prevent HTLV infection.