Adeno-Associated Virus (AAV)

Parvoviridae, dependovirinae


"Dependency is a beautiful thing."

However, this is an EM of herpes virus, a helper virus.
Picture courtesy of Linda M. Stannard, Univ. of Cape Town,
The dependoviruses are an interesting genera of viruses in that they require co-infection by another "helpers" virus in order to successfully replicate. However, even during a productive infection, there is no disease associated with AAV infection. Because of this, the incubation period for the virus is not known. There are no vaccines and there is no treatment or prophylaxis either, since there really isno need for either.

Adeno-associated virus attacks a wide range of cells, using integrins as its binding receptor (integrins are common to many cells in the body as they are used for cell adhesion and signalling). In order for the virus to begin replicating, they host cell must also be infected with either an adenovirus or a herpesvirus to push the cell into mitosis. Interestingly enough, during productive infection, AAV inhibits the lytic replication and the oncogenicity of the helper virus. In the absence of a helper virus, AAV stably integrates into the host genome and waits (considered a latent infection if the virus actually causes disease). The virion itself is very hardy, as it can survive outside a host cell for several weeks. AAV is transmitted via respiratory and fecal/oral routes.

One real risk associated with AAV infection inolves the simple fact that the virus does integrate itself into the host genome. Any AAV recombinants that lose their integration-site specificity can then integrate randomly into the host genome. This insertional mutagenesis could lead to the formation of cancer or other cellular problems, though this has never been documented. This also has positive implications as well: AAV is a great candidate for use as a vector for gene therapy in man. Since it can integrate into human genomic DNA without causing disease, it can be used to replace defective genes in people with genetic disorders. The anti-tumor activity that it displays with its helper virus may also be useful in fighting certain virally-induced cancers.