Introduction:
Papillomaviruses (PVs) are fascinating double-stranded circular DNA viruses that have intrigued researchers for decades. These tiny infectious agents have a unique genome structure, consisting of early (E) and late (L) genes. With their species specificity, PVs tend to exhibit a preference for certain types of epithelium and even specific body locations[^1^]. PVs can infect a wide range of species, including mammals, birds, and reptiles[^3^]. While most species get infected by multiple PV types within different genera, some viruses specialize in closely related hosts, leading to similar lesions[^2^]. In this article, we will delve into PVs in domestic cats, examining their impact on feline health.
The Life Cycle of PVs:
PVs have developed a sophisticated life cycle that closely aligns with the division and differentiation of cells in mucocutaneous stratified epithelium[^4^]. The journey begins with a microtrauma that allows the PV to enter the basal cells. The expression of E1 and E2 genes initiates self-replication, infecting the surrounding basal cells[^4^]. Persistence of PV infection occurs in basal cells, but viral replication only takes place when a basal cell terminally differentiates and enters the suprabasilar layer of the epithelium[^4^]. At this stage, the PV interferes with cell regulation, preventing cells from differentiating, and instead forcing them to divide and replicate the virus[^4^]. As the infected cells near the surface, the virion is assembled, and the viral particles are released into the environment through normal epithelial cell degeneration[^4^].
Visible Lesions and Immune Response:
The development of visible lesions following PV infection depends on the level of epithelial replication and viral replication stimulated by the virus[^5^]. In many cases, PV infections result in slow viral replication and mild increases in epithelial cell replication, which are clinically undetectable[^5^]. These asymptomatic infections seem to be prevalent in both humans and domestic animals[^6^]. However, some PV types exhibit rapid replication, leading to marked epithelial replication. The thickening and folding of the epithelium caused by rapid viral replication manifest as hyperplastic viral papillomas, commonly known as warts[^1^][^7^].
PV infections generally elicit a mild inflammatory response, especially when slow replication and asymptomatic cases are involved[^8^]. The body mounts a cell-mediated immune response to detect and attack infected cells, limiting PV replication[^9^]. This immune response aids in the resolution of hyperplastic lesions induced by PV infection. However, the timing of the immune response onset varies, which explains why some oral papillomas in dogs can persist for up to a year[^10^]. Although the immune system controls PV replication, the virus can persist in basal cells and continue replicating at a low rate. Notably, skin infections by human betapapillomaviruses remain invisible in immunocompetent individuals, whereas immunosuppression can lead to multiple hyperplastic plaques[^6^][^11^]. Similarly, PV-induced pigmented plaques on the skin have been associated with chronic immunosuppressive therapy in dogs[^12^]. Additionally, PV infections trigger the production of serum antibodies, protecting against subsequent infections by the same PV type[^13^].
PVs and Cancer:
Beyond the development of hyperplastic papillomas, PVs can influence the development of cancer[^4^]. In humans, PVs are the leading viral cause of cancer, with high-risk alphapapillomaviruses accounting for approximately 5% of all human cancers, including cervical squamous cell carcinomas (SCCs) and oral SCCs[^14^]. Similarly, PVs have been linked to neoplasia in various domestic species, such as horses, dogs, cattle, pigs, and sheep[^15^][^16^][^17^][^18^][^19^]. However, it is important to note that the majority of PV infections in humans and animals do not result in neoplasia. Other factors, such as the speed of the immune response or other promoters of neoplasia, play critical roles in determining whether a PV infection leads to cancer[^8^][^20^].
PVs in Domestic Cats:
Infections by PVs are widespread in cats, similar to other species[^21^]. However, PV-induced diseases appear to be relatively rare compared to other domestic animals[^22^]. Researchers have investigated the potential PV etiology within feline lesions, leading to several fully sequenced PV types that are known to infect cats. These PV types will be reviewed, and the diseases associated with PVs in cats will be explored. The article concludes with a consideration of the potential use of vaccines to prevent PV-induced diseases in cats.
To learn more about PVs in cats and their impact on feline health, visit Katten TrimSalon.
[^1^]: Reference 1
[^2^]: Reference 2
[^3^]: Reference 3
[^4^]: Reference 4
[^5^]: Reference 5
[^6^]: Reference 6
[^7^]: Reference 7
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[^9^]: Reference 9
[^10^]: Reference 10
[^11^]: Reference 11
[^12^]: Reference 12
[^13^]: Reference 13
[^14^]: Reference 14
[^15^]: Reference 15
[^16^]: Reference 16
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[^20^]: Reference 20
[^21^]: Reference 21
[^22^]: Reference 22