What is HTLV-2?
HTLV-2 stands for "Human T-Lymphotropic Virus type 2". 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. Less is known about HTLV-2 than is known about HTLV-1.
Who is infected with HTLV-2?
HTLV-2 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-2 infection has spread among injecting drug users (IDUs) particularly in America, South Vietnam and Europe. In Europe the highest rates of HTLV-2 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 than the number infected with HTLV-1. Less than 10% of all HTLV diagnoses in the UK have been due to HTLV-2 and only 1 in 100,000 blood donors in the UK was found to carry HTLV-2 compared with 1 donor in 20,000 for HTLV-1. How these people have become infected with HTLV-2 is often uncertain as on many occasions no risk factors are identified.
How does HTLV-2 infection occur and how can infection be prevented?
HTLV-2 infection is transmitted from person to person by one of four possible routes:
• From an infected mother to her baby. Most infections occur through breastfeeding. Research from Brazil and Argentina suggests that around 30% of breastfed infants become infected. If a mother is infected she should avoid breastfeeding and use formula feeds only. A few infections occur either before delivery or during labour.
• HTLV-2 infection is not routinely tested for in the UK ante-natal clinics so if you are pregnant and think you may be a carrier, you need to speak to your doctor or midwife.
• Between sexual partners through unprotected (no condoms) intercourse. The use of condoms, which protect against other infections, is likely to prevent most sexual transmission of HTLV-2.
• Through transfusion of blood from a HTLV-2 infected donor. Only blood products that contain white blood cells, such as whole blood, red blood cells and platelets contain the virus. Plasma is not infectious.
• By the sharing or re-use of needles and syringes to inject drugs. The use of disposable equipment for injections prevents transmission.
• Persons with HTLV-2 infection should not donate blood, organs or sperm and should not carry an organ donor card.
• HTLV-2 infections are detected by the screening tests used by the National Blood Service in the UK to identify HTLV-1 infection in blood.
• One suspected case of HTLV-2 transmission to a healthcare worker has been reported but this has not been proven.
How would I know if I am HTLV-2 infected?
Most people who are infected with HTLV-2 are unaware of this infection. You may have been tested or may wish to be tested because:
• You are a blood or tissue donor and have been screened for HTLV-1 and HTLV-2 as well as other infections.
• A family member or your partner is infected with HTLV-2 and you have been tested through a contact-tracing programme.
• You have developed symptoms which resemble those the virus can cause.
• You have been found to have another viral infection with similar routes of transmission e.g. Hepatitis C virus or HIV.
The only way to find out if you are infected is to perform a special blood test which detects HTLV-2 antibodies. The presence of HTLV antibodies is proof of infection. The test may show negative if infection has only just occurred. If recent infection is suspected the antibody test should be repeated three months later (see section on HTLV-1 window). The screening test for HTLV-1 also detects HTLV-2 and confirmatory tests are required to distinguish between these infections. This is important as the risk of disease differs substantially between these two viruses, being much lower for HTLV-2.
What happens after somebody has been infected with HTLV-2?
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-2 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.
Does HTLV-2 cause any disease?
The vast majority of persons infected with HTLV-2, greater than 99%, do not develop any disease due to HTLV-2. The virus appears to remain in the body throughout life without causing any harm. HTLV-2 disease associations are less well established than those of HTLV-1 but HTLV-2 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-2 infected carriers in North America shows that people infected with HTLV-2 have a small increased risk of bacterial infections, particularly of the chest and bladder.
Can HTLV-2 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 reduce inflammation can also be tried. At present there is no cure for the infection. Any treatments to reduce or eliminate the virus would have to be extremely safe since infection is rarely associated with any health problem.
What is the difference between HTLV-1 and HTLV-2?
HTLV-1 and HTLV-2 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-1. HTLV-1, but not HTLV-2, can also cause leukaemia - a blood cancer.
The screening tests detect both HTLV-1 and HTLV-2 infections. Further tests are necessary to distinguish the two viruses.
The National Centre for Human Retrovirology Clinic Imperial College Healthcare NHS Trust, Ground Floor, Winston Churchill Wing, St Mary's Hospital, Praed Street, London W2 1NY