Human T-Cell Lymphotropic Virus

Sample

1. The serum of the patient is needed.
2. A random sample may be used.

Purpose of the test (Indication)

1. This is used to diagnose a certain type of leukemia (T-cell leukemia).
2. To diagnose demyelinating neurological disease.

Definition of Human T-Cell Lymphotropic Virus (HTLV)

1. HTLV-I
   1. This virus is closely related to retroviruses and is mostly like HIV-I.
   2. Its transmission is also like HIV-I.
   3. HTLV-I  lymphotropic, the retrovirus is the causative agent of cutaneous T-cell lymphoma in adults and nervous system degenerative disorder called tropical spastic paraparesis.
2. HTLV-II
   1. It is not conclusively associated with specific diseases.

Pathophysiology of Human T-Cell Lymphotropic Virus (HTLV)

1. These are oncogenic RNA retroviruses :
   1. HTLV-I is associated with T-cell leukemia/ lymphoma.
      1. It is endemic in certain parts of the Japan and Caribbean basin.
      2. There are large lymphocytes, multilobulated nuclei like monocytes.
      3. It is rarely associated with neurologic conditions like tropical spastic paraparesis.
   2. HTLV-II is associated with:
      1. There are no clearcut associations but seen in a few following condtions.
      2. Demyelinating neurological disorder (tropical spastic paraparesis).
      3. Hairy cell leukemia.
2. This is human retrovirus belongs to the Retroviridae family in the genus Deltaretrovirus.
   1. Retroviruses are RNA viruses with the presence of reverse transpeptidase enzyme which converts RNA virus to DNA virus which incorporates into the genome of the host and mostly affects T-lymphocytes.

HTLV-I and difference from the HIV-I:

1. HTLV-I does not cause depletion of the T-helper cells (CD4+ cells).
2. It is generally not associated with immunosuppression.
3. It does not cause AID syndrome.
4. The presence of the antibodies does not indicate HIV-I infection or risk of AIDS.
5. This is endemic in southern Japan, a Caribbean island, South America, and areas of Africa.

Distribution of the HTLV-I/II

1. HTLV-I is found predominantly in:
   1. Southern Japan.
   2. Some of the Caribbean islands.
   3. Parts of Central and South America.
   4. Sub-Saharan Africa.
   5. >10% of the people in the endemic area are seropositive. This virus is found in 50% of the relatives of virus-positive leukemic patients.

Mode of spread. This is like HIV:

1. Body fluids contaminations.
2. Intravenous drug use.
   1. HTLV-I is seen in I/V drug users in the USA (20% to 25%).
   2. HTLV-I has also been seen in prostitutes (7%).
3. Sexual transmission.
4. Breastfeeding. There is a risk of 20% spread to infants depending upon the duration of breastfeeding.
5. In the USA HTLV-I has been found in:
   1. Patient with ATL (adult T- cell leukemia).
   2. Intravenous drug users.
   3. Donated blood products.
      1. There are 40% to 60% chances of seroconversion in the contaminated blood.
      2. While more risk to the immunocompromised patient.
6. Even in healthy persons.
7. In the case of transplantation of the liver, kidneys, and lungs.

HTLV-I role for T-L leukemia/lymphoma:

1. HTLV-I genome structure consists of gag, pol, env, and long terminal repeat (LTR), like other retroviruses.
2. There is another region labeled as the tax (TAX) gene.
   1. This tax gene can cause viral replication and also acts of LTR.
   2. There is a transcription of the viral mRNA.
   3. tax protein also activates several host genes in the lymphocytes.
   4. There is activation and the proliferation of the T-lymphocytes (CD4⁺).
   5. THis HTLV-I virus causes the expansion and the nonmalignant proliferation of the T-L (CD4⁺).
   6. There increased risk for mutation and gene instability.
   7. Ultimately there is the emergence of the monoclonal T-L emergence and leads to T-L leukemia/lymphoma.

Normal

• Antibodies are negative.

Lab Diagnosis of Human T-Cell Lymphotropic Virus:

1. Serologic tests show HTLV-I antibodies by ELIZA.
2. HTLV-I antibodies are seen in:
   1. Adult T-cell leukemia/lymphoma.
   2. Degenerative neurological diseases are called Tropical spastic paraparesis in Caribean islands.
      1. It is seen in 5% of the general population and 15% of the older people.
   3. HTLV-I myelopathy is seen in Japan.
      1. <15% of the general population of Japan and <30% of the older people.
   4. It is seen is prostitutes in the USA
   5. These are seen in I/V drug abusers.
   6. It is seen in multiple blood transfusions.
   7. Rarely seen in homosexuals males.
   8. These antibodies are not seen in hemophiliacs.
   9. It is seen in 0.025% of random blood donors.
3. These tests also detect HTLV-II.
4. Western blot test is done to confirm the serologic tests.
5. The nucleic acid probe with PCR enhancement is the most sensitive test to differentiate HTLV-I and HTLV-II.

Positive HTLV antibodies are seen in:

1. Acute HTLV infection.
   1. HTLV-I
2. Adult T-cell leukemia.
3. Tropical spastic paraparesis.
4. Hairy cell leukemia.

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