Canine Papilloma Virus
A Microbial Biorealm page on the genus Canine Papilloma Virus
Part of the Papillomaviridae family
Description and significance
Canine Papilloma Virus, more commonly referred to as dog warts, is a common virus in dogs as well as other mammals. It is typically found in the mouths of dogs and is known to be extremely painful. The virus appears as sores, or warts, that are a variety of shapes and sizes. Multiple papillomas, papillomatosis, of skin or mucosal surfaces are more common in younger animals whereas single papillomas are more common in older animals. Dogs are more susceptible when they have weaker immune systems and because the disease is transferred orally from dog to dog, it is important to not allow infected dogs to share food bowls, drinking water and to monitor how they are interacting with other dogs in day to day encounters. The disease is spread by contact with an infected dog, but is transmissible only to dogs and not to other humans or animals. The most preventative method of keeping a dog healthy from the virus is making sure the dog’s immune system is as strong as possible. This means ensuring that the canine is up to date on all of its yearly vaccinations and has regular physical examinations with a veterinarian. In addition, it is important to check the mouths and teeth of canines on a fairly regular basis for sores. The virus is sneaky in that it can lay dormant in a canine for weeks before showing signs of infection and can also re-occur again after an initial breakout. The disease is also capable of clearing up, meaning displaying no visible signs on the dog physically, but still continuing to be active inside the dog.
The papilloma virus genome is a double stranded circular DNA molecule that is approximately 8,000 base pairs in length. All papilloma viruses have similar genomic organizations and usually exhibit five homologous genes with one another. However, despite these similarities, the nucleotide sequences of different species papilloma viruses may differ by more than 50%. There is basically no inter-species transmission of papilloma.
Cell structure, metabolism & life cycle
Papilloma viruses are small, double stranded DNA viruses and because of this are very stable, which is probably why they are known to evolve so slowly. They are highly host and tissue tropic and replicate exclusively in the basal layer of body surface tissues in structures known as keratinocytes. Keratinocytes form the outer most layer of the skin and are made of stratified squamous epithelia. In order to replicate they use the replication machinery of their hosts. Papilloma viruses are non-enveloped which means that the outer shell of the virus is not covered with a lipid membrane. Proteins, L1 and L2, are responsible for formation of this outer structure. In dogs, there are six distinct papilloma viruses and this number varies across different mammalian species. The canine papilloma virus is known to have a fairly long incubation period, about 1-2 months duration.
Ecology (including pathogenesis)
Papilloma viruses enter canines through small wounds on the skin or mucosal surface. This is when the virus is initially attached to the host and after successful invasion of the canine body moves into the keratinocyte. In the keratinocyte the papilloma virus can replicate repeatedly and this structure can also maintain the virus genome for decades, which is problematic to the host. The canine that is infected will display warts on all mucosal surfaces, especially the mouth area.
An interesting feature about canine papilloma virus is that in dogs, there are three different clinical signs of the virus: canine mucous membrane papillomatosis, cutaneous papillomas and cutaneous inverted papillomas. These three different types of the virus affect young, old and mature dogs respectively. Multiple warts on the oral mucous membranes, from the lips to the esophagus, characterize canine mucous membrane papillomatosis. In severe cases, these warts can greatly interfere with swallowing and mastication. Warts that develop from cutaneous papillomas are similar to those developed in mucous membrane papillomatosis, with the exception of these warts tending to be more solitary and not found clustered together. The last clinical sign of the virus is cutaneous inverted papillomas in which lesions are aggregated mostly on the abdomen rather than any other part of the canine body.
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