What is being tested?
Human T-lymphotropic virus (HTLV) infection is associated with certain rare diseases of T lymphocytes (T-cells), a type of white blood cell that is an important part of the body’s immune system. This test detects an HTLV infection in order to help identify the virus as the underlying cause of an individual’s leukemia, lymphoma, rare nervous system disorder, chronic pulmonary infection, uveitis, infectious dermatitis, or other inflammatory disorder.
Two types of HTLV are most commonly identified through testing: HTLV-I and HTLV-II. It is estimated that 15-20 million people worldwide are infected with HTLV. The prevalence of HTLV-1 infection is greatest in Japan, sub-Saharan Africa, the Caribbean islands, and Central and South America. HTLV-II appears to be endemic among Native American populations and is prevalent among intravenous (IV) drug users in North America and Europe.
In the United States, about 22 out of every 100,000 people are infected with HTLV, with HTLV-II infection being more common than HTLV-I infection. HTLV-II infection is associated with female sex, older age, non-white race/ethnicity, lower educational level, and residence in the Western and Southwestern U.S. Some Native American Indian populations have infection rates as high as 13%. Those most likely to be infected with HTLV-I have immigrated to the U.S. from a country where HTLV-1 infection is prevalent, are children of such immigrants, are IV drug users, or are sex workers.
An HTLV-I infection can be passed from mother to child during pregnancy or breastfeeding. Both HTLV-I and HTLV-II infections can be sexually transmitted or spread through exposure to contaminated blood as occurs with sharing of needles during IV drug use, although the majority of drug use-related infections are linked to HTLV-II. Both types may be passed through a blood transfusion or an organ transplant, but infection due to these procedures is now rare in the United States because all donors are tested for HTLV-I/II.
Other risk factors for HTLV infection include: living in parts of the world where HTLV is more common (such as those listed above); having a sexual partner who came from one of these areas; having multiple sex partners; being an IV drug user; being Native American Indian; or having a history of blood transfusions.
Both HTLV-I and HTLV-II preferentially infect T-lymphocytes. Most people infected with HTLV-I or HTLV–II will have few to no symptoms but can pass the infection on to others. After the initial infection, the virus never completely goes away but remains in the body in an inactive (latent) form. A small percentage of those infected go on to develop one of several associated diseases, typically months to many years or even decades after their initial exposure, and may then become acutely or chronically ill.
HTLV-I is associated with:
- Adult T-cell leukemia/lymphoma (ATL), a type of white blood cell cancer that may progress rapidly or slowly and cause symptoms such as fatigue, fever, and enlarged lymph nodes
- HTLV-I–associated myelopathy/tropical spastic paraparesis (HAM/TSP), a rare condition that can cause weakness in the lower limbs, muscle spasms, nerve pain, and urinary incontinence
- In some cases, other conditions such as uveitis, HTLV-I–associated infective dermatitis, rheumatoid arthritis, and Sjögren syndrome
HTLV-II is less clearly linked with specific diseases but may be associated with certain lung conditions, neurological disorders, arthritis, asthma, and dermatitis.
The body responds to an HTLV-I or HTLV-II infection by producing antibodies. These antibodies can be detected in the blood during testing. The viruses may also be directly tested using molecular tests (polymerase chain reaction, PCR) that detect the genetic material of the viruses.
How is it used?
Human T-lymphotropic virus (HTLV) testing is used to detect an infection by HTLV-I or HTLV-II. When the virus enters the body, it preferentially infects T-cell lymphocytes. The body’s immune system responds by producing antibodies that target the virus. Most individuals who are infected do not develop an active illness, but a rare few will develop a condition related to a disorder of the T-cells.
HTLV testing may be used in a few different ways:
- In people with risk factors for HTLV (such as living in parts of the world where HTLV infection is more common, having a sexual partner who came from one of these areas, having multiple sex partners, being an IV drug user, being a Native American Indian, or having a history of blood transfusions), testing may be used to follow-up abnormal findings from a complete blood count (CBC) and WBC differential, such as an increased number of immature and/or abnormal lymphocytes.
- To diagnose the cause of a T-cell-related disorder if a person has symptoms consistent with HTLV-I–associated myelopathy/tropical spastic paraparesis (HAM/TSP), especially if the person has risk factors associated with this condition; in some cases, cerebrospinal fluid (CSF) may be tested for HTLV.
- To determine the source of an affected individual’s infection; since HTLV can be passed from mother to baby during pregnancy, the mother of an affected child may be tested for HTLV-I or HTLV-II to determine if she is the likely source of the child’s infection. Likewise, the sexual partner of an affected person may be tested.
Two types of HTLV testing are available, antibody and molecular testing:
- Typically, an EIA (enzyme immunoassay) test method is used initially to detect HTLV-I and HTLV-II antibodies in the blood. If the initial test is positive, a second method, such as Western blot, is ordered to confirm the finding and to help distinguish between HTLV-I and HTLV-II.
- In cases where HTLV-I and HTLV-II cannot be distinguished, molecular testing (polymerase chain reaction method, PCR) that detects the genetic material of the virus may be performed.
In the U.S., all donated blood is screened for HTLV. If a person who has donated blood tests positive for HTLV-I/II, then confirmatory testing may be performed to determine if the initial screening result is a false positive or if the person who donated the blood has an HTLV-I/II infection.
When is it ordered?
HTLV testing may be performed when a person has symptoms or findings that suggest that the person has a condition associated with an HTLV-I or HTLV-II infection, especially when that person also has identified risk factors.
Signs and symptoms of adult T-cell lymphocytic leukemia or lymphoma may include:
- Night sweats
- Increased number and abnormal immature lymphocytes
- Enlarged lymph nodes
Symptoms of HTLV-I–associated myelopathy/tropical spastic paraparesis (HAM/TSP) may include:
- Weakness in the lower limbs
- Muscle spasms and contractions
- Lower back pain
- Muscle stiffness
- Urinary, bowel, and sexual dysfunction
Testing may be performed on:
- A mother when her child has been diagnosed with an HTLV infection
- The sexual partner(s) of a person when that person has been diagnosed with an HTLV infection
- A person when he or she has been told that the blood that the person donated was positive for HTLV-I/II
- A person when he or she has risk factors and symptoms that the healthcare practitioner suspects may be linked to an HTLV infection, such as uveitis, dermatitis, or arthritis
What does the test result mean?
HTLV testing is usually done in a stepwise fashion and usually includes an initial test followed by confirmatory testing, depending on the results.
If initial HTLV testing is negative, then it is unlikely that the individual has an HTLV infection and the person’s symptoms are likely due to another cause. Typically, no further testing is necessary.
If someone has HTLV-I or HTLV-II antibodies on both initial and confirmatory testing, then it is likely that the person has an HTLV infection. If the person also have symptoms linked to an HTLV-associated condition, then it is likely that this infection is the underlying cause.
A person with positive initial and confirmatory results but no symptoms, such as someone who has been tested because she is the mother of an affected child or the sexual partner of an affected person, or someone whose donated blood was positive and confirmatory testing is also positive, is likely to have the infection. However, in the vast majority of cases, the person will never develop an illness. These people can, however, pass the infection on to other people and should take necessary precautions.
Those who have a positive initial HTLV-I/II test and a negative confirmatory test likely have a false positive and not an HTLV infection. Those with an indeterminate confirmatory test result should be retested in several weeks to determine if they have developed antibodies. If the confirmatory testing is negative or still indeterminate, then it is unlikely that the person has an HTLV infection.
A positive HTLV-I/II molecular test indicates that the person tested has an HTLV-I or HTLV-II infection. If the molecular result is negative, then the person is less likely to be infected, but it cannot be ruled out as the amount of virus in the blood may have been too low to detect at the time of the test.
The following table summarizes some typical results that may be seen with HTLV testing:
|Initial Antibody Testing (HTLV I/II)||Confirmatory Testing (Western blot)||Additional Testing||Likely Interpretation|
|Positive||Negative||Repeat Western blot negative||False positive on initial test|
|Positive||Positive HTLV-I||N/A||HTLV-I infection|
|Positive||Positive HTLV-II||N/A||HTLV-II infection|
|Positive||Indeterminate||Molecular test (PCR) positive or repeat Western blot positive for HTLV-I or HTLV-II||HTLV-I or HTLV-II infection|
|Positive||Indeterminate||Molecular test (PCR) negative or indeterminate and repeat Western blot negative or still indeterminate||Likely false positive on initial antibody testing|
Is there anything else I should know?
The HTLV-I/II viruses become inactive (latent) in the body after an infection, but they are never totally eradicated. For this reason, a person who has tested positive will not be able to donate blood.
HTLV-II antibodies may show a positive result on a test for HTLV-I antibodies (cross-reaction). This means that even though a person has really had an HTLV-II infection, initial testing may show an HTLV-I positive test result.
Should everyone be tested for HTLV-I/II?
No. The incidence of HTLV-I/ll is low in the United States and most people who are infected do not ever become ill, so it is not considered necessary. However, since the viruses can be passed from one person to another through blood transfusions and organ transplants, all donated blood (since 1988) and all relevant donated organs are tested for HTLV-I/II.
Should I be tested for HTLV-I/II if I have some of the risk factors?
This would be something to discuss with your health care practitioner. If you have risk factors, such as you have lived in one of the countries where these infections are more common, have had multiple sex partners, have been an IV drug user, or are a Native American Indian, then you and your healthcare practitioner may want to consider it.
I found out I am positive for HTLV. What precautions should I take to avoid infecting others?
You can take several steps to avoid spreading the infection, according to the Centers for Disease Control and Prevention:
- Tell your health care practitioner that you have been infected; he or she can speak with you about necessary precautions.
- Do not donate blood, tissues, organs, or sperm.
- If you are a new mother, do not breastfeed.
- Do not share needles or syringes.
- Use condoms to prevent sexual transmission.
Can I get HTLV-I/II from donating blood?
No, blood collection is performed using a sterile needle. You cannot get an HTLV infection from donating.
The names HTLV and HIV look and sound similar – are these diseases related?
They both belong to the same group of viruses known as retroviruses and can be passed through blood and sexual contact, but they are only very remotely related, and HTLV does NOT cause AIDS and does not have the same devastating effects on a person’s immune system that HIV does.
HTLV and HIV do, however, share a historical naming convention. HTLV-III was the name given to HIV (human immunodeficiency virus) when it was first identified. The virus was later reclassified and the name was changed to HIV. Since that time, the term HTLV-III has been re-used to designate a different HTLV virus. The newly designated HTLV-III virus, as well as an HTLV-IV virus, have been identified and are being studied, but testing of them is only being done on a research basis.
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