Papovaviridae

Papovaviridae

The Papovaviridae was a family of DNA viruses that included two genera: Polyomavirus and Papillomavirus. This family is no longer used in current virus taxonomy, as the two genera have been reclassified into separate families. However, understanding the historical classification of Papovaviridae is important for comprehending the evolution of virus taxonomy and the characteristics of these viruses.

History and Classification

The name "Papovaviridae" was derived from the first two letters of three viruses: Papillomavirus, Polyomavirus, and Vacuolating virus (SV40). The family was established in the 1960s when these viruses were grouped together based on their similar properties, such as their small size, circular double-stranded DNA genomes, and ability to induce tumors in animals.

In the late 20th century, advances in molecular biology and virology led to a better understanding of the genetic and structural differences between papillomaviruses and polyomaviruses. As a result, the International Committee on Taxonomy of Viruses (ICTV) reclassified these viruses into separate families:

• Papillomaviridae: This family includes the papillomaviruses, which are known to cause warts and are associated with various cancers, such as cervical cancer.
• Polyomaviridae: This family includes the polyomaviruses, which are known to cause diseases in immunocompromised individuals and have been studied for their oncogenic potential.

Characteristics

Genome

The viruses that were once classified under Papovaviridae have circular, double-stranded DNA genomes. The genome size varies between the two genera, with papillomaviruses having genomes of approximately 8,000 base pairs and polyomaviruses having genomes of about 5,000 base pairs.

Structure

These viruses are non-enveloped and have icosahedral capsids. The capsid is composed of protein subunits that protect the viral DNA and facilitate its entry into host cells.

Replication

Replication of these viruses occurs in the nucleus of the host cell. They rely on the host cell's machinery to replicate their DNA and produce viral proteins. The life cycle of these viruses is closely linked to the differentiation state of the host cell.

Pathogenesis

Papillomaviruses

Papillomaviruses infect epithelial cells and are known for causing benign tumors, such as warts. Some types of human papillomaviruses (HPVs) are associated with malignant tumors, including cervical cancer, anal cancer, and oropharyngeal cancer.

Polyomaviruses

Polyomaviruses can cause disease in immunocompromised individuals. For example, the JC virus can cause progressive multifocal leukoencephalopathy (PML), a demyelinating disease of the central nervous system. The BK virus can cause nephropathy in kidney transplant recipients.

Research and Clinical Implications

The study of these viruses has provided significant insights into viral oncogenesis, the process by which viruses can induce cancer. Vaccines have been developed against certain high-risk types of HPV, significantly reducing the incidence of cervical cancer.

Also see

• Papillomaviridae
• Polyomaviridae
• Viral oncogenesis
• Human papillomavirus
• SV40

Virus classification

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Diagram of a virus structure