HTLV (Human T-lymphotropic virus)
Date: 2 سال قبل
HTLV (Human T-lymphotropic virus)
The human T-lymphotropic virus or human T-cell leukemia-lymphoma virus (HTLV) family of viruses are a group of human retroviruses that are known to cause a type of cancer called adult T-cell leukemia/lymphoma and a demyelinating disease called HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). The HTLV genome is diploid, composed of two copies of a single-stranded RNA virus whose genome is copied into a double-stranded DNA form that integrates into the host cell genome, at which point the virus is referred to as a provirus.
How is HTLV infection transmitted?
HTLV infection can be transmitted via 3 main routes:
· Via unprotected sexual contact.
· Via contaminated blood transfusions or blood products1, sharing contaminated needles and other injection equipment, self-flagellation, or receiving an organ or tissue transplant from an infected donor.
· HTLV virus can be passed from an infected mother to her baby mainly via breast feeding (predominantly with prolonged breast feeding beyond 6 months of age) and less commonly during the pregnancy (intra-uterine transmission).
What diseases does HTLV cause?
In the majority of infected individuals there is an asymptomatic carrier state (silent but ongoing infection), with only a small proportion (about 5 to 9%) developing disease associated with HTLV-1 during their lifetime.
HTLV-1 infection gives rise to two main disease entities:
· Adult T-cell leukaemia/lymphoma (ATLL) which is a form of blood cancer
· HTLV-associated myelopathy (HAM)
ATLL occurs in approximately 5% and HAM in approximately 3% of carriers.
In a smaller number of patients, other inflammatory conditions such as uveitis (inflammation of the eye), arthritis (inflammation of joints), myositis (inflammation of muscles), alveolitis (inflammation of lungs) and dermatitis (inflammation of skin) can be seen.
The HTLV-2 disease spectrum is less clear, but lung conditions, myelopathy (inflammation of the spinal cord) and dermatitis, have been reported.
Sometimes, as HTLV causes mild immunosuppression, patients may develop diseases caused by other infectious agents that are able to thrive in a host with a suppressed immune system (e.g. parasitic infections such as Strongyloides stercoralis).
What tests are performed?
- Serology: Once individuals are infected with HTLV, their immune system starts producing antibodies that are specifically directed against the virus. By detection of these antibodies using laboratory tests, whether or not a person is infected with this virus can be determined. Using the development of antibodies to detect infection is called serology.
- Molecular: Sometimes a test to detect the genetic material of the virus is used. This can be useful in situations such as having indeterminate serology (inconclusive antibody) test results or when antibodies to both HTLV-1 and HTLV-2 are detected. The measurement of HTLV-1 viral load in patients found to be infected is also useful to determine risk of disease and sometimes to aid with the diagnosis and treatment of an HTLV-1-associated disease. Detection and quantification of HTLV-genetic material is called molecular diagnostics.
Prevention and treatment
There is currently no vaccine for HTLV-1, although development of a vaccine is considered feasible. However, animal models may not be suitable to study vaccine effects in HTLV-1. No candidate HTLV-1 vaccine has proceeded to a clinical trial with an efficacy endpoint so far.
No treatment is currently recommended for people with asymptomatic HTLV-1 infection. Treatment should instead focus on the symptoms of associated diseases, namely ATL and HAM/TSP, and screening for comorbidities and coinfection.