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[Japo]

Originally Posted by Lulu_Jane

The list of incurable diseases is actually pretty huge.

Plus,

Because reverse transcription lacks the usual proofreading of DNA replication, this kind of virus mutates very often. This enables the virus to grow resistant to antiviral pharmaceuticals quickly, and impedes, for example, the development of an effective vaccine against the retrovirus HIV.

http://en.wikipedia.org/wiki/Retrovirus