adeno-associated virus or AAV – AAV is a defective parovirus with a single-stranded DNA genome and a naked protein coat. AAV is in the dependovirus division of the parvovirus family. One of the main distinguishing features of AAV is that it requires a helper virus (for example, herpes or adeno virus families) for productive growth, in the absence of a helper virus no progeny virus is produced but the AAV integrates into the host chromosome at a very low frequency.