• HTLV-I is a member of the Family Retroviridae, genus Deltaretrovirus.
• The virion is roughly spherical, enveloped and contains 2 identical strands of positive sense, single-stranded RNA.
• Worldwide distribution, but predominantly found in southern Japan, Africa and the Caribbean. Seroprevalence in the USA is <1%.
• Transmission occurs from mother to child at birth or through breast feeding, through blood transfusions, contaminated needles, and sexual contact.
• Retroviruses have a unique method of replicating, which involves a reverse transcriptase (RT) that transcribes the genomic RNA into a complementary DNA copy (termed a provirus) which then integrates into the host cell genome.
• Transmission is generally via infected lymphocytes rather than cell-free virus. HTLV-I infects CD4 lymphocytes and dendritic cells, with viral entry via direct cell-to-cell contact.
• HTLV-I does not induce T cell death (as with HIV) but rather causes cell transformation and cell proliferation.
• Infection is usually asymptomatic with approximately 5% developing disease.
• Two well recognized diseases are associated with infection: adult T-cell leukemia/lymphoma (ATLL) and a chronic degenerative neurologic disease known as HTLV-I associated myelopathy (HAM) also known as tropical spastic paraparesis (TSP). ATLL generally has a long latent period of approximately 20-30 yrs, however, it is usually fatal within a year of diagnosis.
• Serology: detection of specific antibody in serum samples (reactive screening tests should be verified by a confirmatory test)
• PCR: detection of proviral DNA in whole blood samples.
• The best therapy for ATLL is unclear, although zidovudine (AZT) plus interferon alpha have been effective in some patients.
• Anti-viral therapy for HAM is not effective, treatment is primarily symptomatic.
Prevention and Control:
• Similar to HIV precautions, screening of the blood supply, clean needle programs, safe sexual practices.
• Maternal transmission via breast milk: bottle feed or freeze/thaw breast milk prior to use.