How did viruses evolve? Are they a streamlined form of something that existed long ago, or an ultimate culmination of smaller genetic elements joined together?

Human retroviruses and AIDS ... Human immunodeficiency virus reverse transcriptase and protease sequence database. Nucleic Acids Res. 27, 348–352 (1999).

Also has developed a new reverse transcriptase inhibitor called "ADAM," and analogs of it are being created ... Studies the envelope proteins of viruses, including retroviruses and the Ebola virus.