Inactivated Wild-Type Human T-Lymphotropic Virus (Type II)

Human T-lymphotropic virus (HTLV) is a retrovirus primarily transmitted through contact with infected body fluids, including blood transfusions, unprotected sexual intercourse, and breastfeeding from infected mothers. Vertical transmission from mother to child is a significant route of transmission, particularly in endemic areas such as Japan, the Caribbean, and parts of Africa. Unlike HIV, HTLV does not replicate extensively in the blood, but instead integrates its proviral DNA into the host T-cell genome, leading to lifelong infection. The virus primarily targets CD4+ T lymphocytes but can also infect CD8+ T cells and dendritic cells. HTLV-1 is the most pathogenic subtype and is associated with adult T-cell leukemia/lymphoma (ATLL) and HTLV-1-associated myelopathy/tropical spastic paraplegia (HAM/TSP).

HTLV has the typical spherical structure of a retrovirus, with viral glycoproteins (gp46 and gp21) embedded within its lipid envelope, facilitating viral entry into host cells. Its core consists of two identical single-stranded RNA genomes and essential enzymes, including reverse transcriptase, integrase, and protease. The HTLV genome is approximately 9 kb long and encodes structural proteins (Gag, Pol, Env) and regulatory proteins (Tax, Rex). It is flanked by long terminal repeats (LTRs) that regulate viral transcription. Unlike HIV, HTLV lacks the vpu gene but possesses unique regulatory genes, such as Tax, which activates viral replication and host cell pathways, and HBZ, which promotes immune evasion and tumor formation. The virus replicates primarily through clonal expansion of infected cells rather than through the production of large quantities of virions, which contributes to its persistence and low mutation rate.