Complex sentence: Infection with HTLV-I, like infection with other retroviruses, probably occurs for life and can be inferred when antibodies against HTLV-1 are detected in the serum.
Split into simpler sentences: Infection with HTLV-I, like infection with other retroviruses, probably occurs for life. A patient infected with HTLV can be diagnosed when antibodies against HTLV-1 are detected in the serum.