"adeno-associated virus" is a small single strand DNA virus. It belongs to the family of the Parvoviridae and in the genus Dependovirus. The viral particle is composed of one positive or negative polarity strand of DNA in a capsid. The mean size of an AAV particle is 18 to 22 nm. AAVs are the only non-autonomous parvoviruses. When we speak of "rAAV", this means the recombinant AAV virus, i.e. modified to become a vector (and thus is no longer infectious).