What is HTLV-II?HTLV-II stands for "Human T-Lymphotropic Virus type II". This virus infects a type of white blood cell called T-lymphocytes which are important in fighting infections. A virus is a tiny organism that cannot be seen without magnification. Viruses do not have a metabolism (life support) of their own and can only live and multiply within a living cell. Once a new virus is formed it is released from that cell and must find a new cell to infect.
Who is infected with HTLV-II?HTLV-II infection has been found in Western Africa and may have originated there. It is thought to have migrated during ancient times with native American Indians to North and South America.
In modern times HTLV-II infection has spread among injecting drug users (IDUs) particularly in America, South Vietnam and Europe. In Europe the highest rates of HTLV-II are found amongst injecting drug users in Eire, Spain, Italy and Scandinavia.
The exact number of people infected in the UK is not known but is much less then the number infected with HTLV-I. For example, only 1 in 100,000 blood donors in the UK was found to carry HTLV-II compared with 1 donor in 20,000 for HTLV-I. How these people have become infected with HTLV-II is often uncertain as on many occasions no risk factors are identified.
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How does HTLV-II infection occur and how can infection be prevented?HTLV-II infection is transmitted from person to person by one of four possible routes:
How would I know if I am infected?Most people who are infected with HTLV-II are unaware of this infection. You may have been tested or may wish to be tested because:
What happens after somebody has been infected with HTLV-II?Cells responsible for the body's defence against infections will recognise the virus as foreign to the body and try to clear the infection. However the body is unable to clear the HTLV-II virus completely. A balance between the virus and the body will be reached, where virus reproduction continues but is controlled by the immune system. This state is called asymptomatic carriage because the infection does not cause disease. In a very few cases, however, symptoms will develop.
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Does HTLV-II cause any disease?The vast majority of persons infected with HTLV-II, greater than 99%, do not develop any disease due to HTLV-II. The virus appears to remain in the body throughout life without causing any harm. HTLV-II disease associations are less well established than those of HTLV-I but HTLV-II has been associated with myelopathy - an inflammation of nerves in the spinal cord - which leads to stiffness and weakness of the legs, backache, a "weak" bladder and constipation. The damage appears to be caused by chemicals released from immune cells fighting the infection which inadvertently harm the nerves. A study of HTLV-II infected carriers in North America shows that people infected with HTLV-II have a small increased risk of bacterial infections, particularly of the chest and bladder.
Can HTLV-II infection be treated?Treatment is not required for asymptomatic patients who are usually followed up in the clinic annually. The various symptoms of myelopathy are treated as required and drugs which may reduce the amount of the virus in the blood or reduce inflammation can also be tried. At present there is no cure for the infection.
What is the difference between HTLV-I and HTLV-II?HTLV-I and HTLV-II are closely related viruses but tend to infect different populations and are associated with different diseases and different rates of disease. Although both can cause a myelopathy, an inflammation of the spinal cord, this is much more common with HTLV-I. HTLV-I, but not HTLV-II, can also cause leukaemia - a blood cancer.
The screening tests detect both HTLV-I and HTLV-II infections. Further tests are used to distinguish the two viruses.
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