Human T-lymphotropic virus (HTLV) is a family of retroviruses that infects humans, primarily targeting T-lymphocytes, a type of white blood cell that plays a significant role in the immune system. HTLV has a global presence, with an estimated 5 to 10 million people infected worldwide. While sharing some characteristics with human immunodeficiency virus (HIV) as a retrovirus, HTLV is distinct in its mechanisms and the diseases it causes.
Understanding HTLV Types and Transmission
The HTLV family includes four recognized types: HTLV-1, HTLV-2, HTLV-3, and HTLV-4. HTLV-1 and HTLV-2 are the most studied types, with the disease potential of HTLV-3 and HTLV-4 still under investigation.
HTLV spreads primarily through direct contact with infected bodily fluids, including blood, breast milk, and semen. Common transmission routes include:
- Mother-to-child transmission, mainly through breastfeeding, with rates around 20–30%.
- Sexual contact, particularly male-to-female.
- Sharing needles or syringes among intravenous drug users.
- Contaminated blood transfusions.
HTLV is not spread through casual contact such as sneezing, coughing, or sharing utensils.
Conditions Associated with HTLV
Most individuals infected with HTLV remain without symptoms throughout their lives. However, a small percentage, approximately 5%, may develop serious health conditions, often years or decades after initial infection. HTLV-1 is known to cause two main diseases: Adult T-cell Leukemia/Lymphoma (ATL) and HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP).
Adult T-cell Leukemia/Lymphoma (ATL) is an aggressive blood cancer that can manifest in various forms. This condition is more commonly linked with vertical transmission from mother to child.
HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP) is a progressive neurological disorder. This condition often leads to symptoms such as progressive weakness and stiffness in the legs, lower back pain, and issues with bladder or bowel control. The lifetime risk of developing HAM/TSP is around 2% for HTLV-1 infected individuals, with a higher incidence in women. Other less common conditions associated with HTLV-1 include uveitis and infective dermatitis. HTLV-2 is less frequently linked to severe diseases, though some associations with milder neurological conditions have been suggested.
Diagnosis of HTLV
Diagnosing HTLV infection typically begins with a screening test, such as an enzyme-linked immunosorbent assay (ELISA), which detects antibodies produced by the body in response to the virus. If the screening test yields a positive result, further confirmatory tests are necessary to confirm the infection and distinguish between HTLV-1 and HTLV-2. These more specific tests often include Western blot or polymerase chain reaction (PCR).
Blood donors are routinely screened to prevent transmission through transfusions. Pregnant women in regions where HTLV is common may also be tested to assess the risk of mother-to-child transmission. Individuals presenting with symptoms suggestive of HTLV-associated diseases, such such as unexplained neurological issues or certain blood disorders, may undergo testing.
Managing and Preventing HTLV Infection
Currently, there is no cure for HTLV infection, meaning that once a person is infected, the virus remains in their body for life. Management of HTLV infection focuses on treating the associated diseases and monitoring asymptomatic carriers for early signs of disease progression. For individuals who develop Adult T-cell Leukemia/Lymphoma (ATL), treatment options may involve chemotherapy, antiviral medications, and in some cases, stem cell transplantation.
For HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP), management primarily involves symptomatic treatment, which can include corticosteroids and other immunomodulating drugs to help manage inflammation and neurological symptoms. Regular medical monitoring for asymptomatic carriers is important to detect any signs of disease development early, allowing for timely intervention.
Prevention strategies are important in controlling the spread of HTLV. Practicing safe sexual behaviors, including consistent condom use, significantly reduces the risk of transmission. Avoiding the sharing of needles or syringes is also an important preventive measure, particularly for individuals who inject drugs. All blood products undergo screening before transfusion to ensure they are free of HTLV. To minimize mother-to-child transmission, avoiding breastfeeding is recommended in high-risk situations when safe alternatives are available.