Adeno associated virus is a helper virus , associated with Adenovirus. It is commonly called AAV. It cannot replicate on its own, it requires a cell to be co-infected with Adenovirus in order to replicate. In the absence of co-infection with Adenovirus, the AAV goes into a latent phase . This latent phase makes AAV attractive for gene therapy applications as a gene of interest in AAV can persist in the host cell genome for a long period. AAV is a small parvovirus, its wildtype genome is 4.7kb. This is the upper limit for its use in gene therapy applications as well.