History and Taxonomy of Papillomaviridae

Warts have been around for… well, basically forever. The ancient Greeks and Romans were no dummies about the infectious nature of warts— but it wasn’t until the early 1900s that a cell-free filtrate was shown to transmit the benign lesions. Richard Shope investigated the cottontail rabbit papillomavirus and discovered the first DNA tumor virus in the 1930s. Interesting bit of Papillomaviridae trivia: it's believed that rabbits infected with the cottontail rabbit papillomavirus are the source of the rumored "jackalope" animal. The protruding warts caused by this virus creates a horn-like effect.

Image above: A proposed origin for the "Jackalope" animal-- in reality, one sick bunny

In the 1950s and 1960s sadly little work was done on Papillomaviruses, however the area experienced a sort of molecular age renaissance following the advent of molecular cloning in the 1970s.

Link to Interactive Papillomaviridae Timeline

Taxonomy and Classification

Papillomaviridae and Polyomaviridae used to be classified together in one viral family named Papovaviridae. No more. In 1994, they were officially split into different taxa forever! Here’s the breakdown of key similarities and differences:

They have a lot in common:

    1. Double-stranded DNA virus with circular genomes
    2. 72 pentamer icosohedral viruses
    3. Both hexavalent and pentavalent capsomers in the capsid
    4. Non-enveloped (naked!)
    5. Virion replication and assembly in the nucleus
    6. Common genetic organization of viral genomes

They are very different:

    1. Different genome sizes— Papillomaviridae 8kbp, Polyoma 5kbp
    2. No major genetic sequence homology
    3. Different capsid sizes— again, Papilloma bigger at 52-55 nm, Polyoma measuring between 40-45 nm
    4. Papillomaviridae encodes all of its genes on one strand: Polyoma does not

Within the family Papillomaviridae, papillomaviruses have mainly been clasiffied by the host species that they infect. Generally speaking, papillomaviruses are very host specific. What's more, within a single host species there are usually multiple strains of papillomavirus that infect that host.

The whole family currently contains 12 genera, named by letters in the Greek alphabet. Within this type of classification, Human Papillomaviruses (HPV) strains can be found in 5 of the 12 genera: alpha, beta, gamma, mu, and nu. The other 7 genera contain only animal viral pathogens. HPV members of the alpha genus primarily infect genital mucosoal surfaces and external genitalia, while human viruses belonging to the beta, gamma, mu, and nu genera tend to infect non-genital skin.

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