HTLV-1 is the causative agent of (a) adult T-cell leukemia (ATL), (b) HTLV-1-associated myelopathy/tropical spastic paraparesis, (c) HTLV-associated uveitis, and (d) HTLV-1-associated infective dermatitis.
Adult T-cell leukemia (ATL) is seen in approximately 1 in 20 persons infected by HTLV-1 over a period of 30–50 years. The condition is a malignancy of the CD4 helper T cells, which can be acute or chronic. Acute ATL comprises 55–75% of all the ATL cases. Lymphade-nopathy (both in the periphery and within the body cavities) repre-sents the classic form of ATL. Hepatosplenomegaly, hypercalcemia, and lytic bone lesions are the other manifestations. Death is caused due to opportunistic infections, pulmonary complications, and sepsis. Chronic ATL is a less common manifestation.
HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a slowly progressing degenerative disease that primarily affects the corticospinal tract of the thoracic spinal cord. The incubation period of HAM/TSP can be as short as 3 months when infection is transmitted by blood transfusion, but is usually 3 years. Patients with HAM/TSP may present with weakness and stiffness in lower limbs, urinary inconti-nence, and lower back pain.
HTLV-associated uveitis is a less frequent manifestation. The condition is associated with the presence of HTLV-infected lymphocytes in vitreous fluid of the eye.
HTLV-associated infectious dermatitis is a chronic and severe form of dermatitis seen during childhood. HTLV-2 has not been associated with any lymphoproliferative disease in humans. It is doubtful that HTLV types 3 and 4 cause any human disease.