EXTREME STREAMLINING. “Some polintoviruses have given up the virus lifestyle altogether by losing the genes involved in virion formation and becoming pure transposons (Polintons). A striking example is the extraordinary expansion of capsid-less Polintons in Trichomonas vaginalis, where they constitute up to 30% of the host genome.”
http://onlinelibrary.wiley.com/doi/10.1111/nyas.12728/full