Feline HPV: Symptoms, Cancer Risk, and Diagnosis

Cats do not catch human HPV, but they harbor their own family of papillomaviruses that work in strikingly similar ways. At least seven distinct papillomavirus types are now known to infect domestic cats, and the most studied of them, Felis catus papillomavirus type 2 (FcaPV-2), uses molecular tricks nearly identical to those of the high-risk human papillomaviruses linked to cervical cancer. The parallel is close enough that veterinary researchers openly borrow language and frameworks from human oncology when studying these feline viruses, yet the public awareness gap is enormous: most cat owners have never heard that papillomaviruses play a role in feline cancer at all.

The Papillomavirus Types That Infect Cats

Papillomaviruses are small, double-stranded DNA viruses that tend to be highly species-specific. The domestic cat has its own growing roster. The first three types to be fully sequenced were originally called Felis domesticus papillomavirus 1 and 2 (FdPV-1, FdPV-2) and Felis catus papillomavirus 3 (FcaPV-3). A fourth type, FcaPV-4, was identified from the oral cavity of a cat and shown to be a close relative of FcaPV-3, with both viruses classified in the genus Taupapillomavirus.¹ A fifth type, FcaPV-5, followed, sharing enough genetic similarity with FcaPV-3 and FcaPV-4 that researchers proposed placing all three in a new genus.² Types 6 and 7 have since been added, and a comprehensive 2021 review counted seven known feline papillomavirus types in total.³

These types are not interchangeable. They belong to different genera, infect different tissue sites, and are associated with different outcomes. FcaPV-2 is the type most closely linked to cancer. FcaPV-1 is associated with cutaneous fibropapillomas, sometimes called feline sarcoids. FcaPV-3, -4, and -5 share a genus but appear in varying lesion types and body sites. The naming can be confusing because the older FdPV designations were eventually harmonized under the FcaPV system, so FdPV-2 and FcaPV-2 refer to the same virus.

What Feline Papillomavirus Infections Look Like

In cats, papillomaviruses are linked to four main types of skin lesion: hyperkeratotic viral plaques, Bowenoid in situ carcinomas (BISCs), invasive squamous cell carcinomas, and cutaneous fibropapillomas or sarcoids.⁴ Cutaneous papillomas, the classic “warts” that dog owners may be familiar with, also occur in cats but are less common. Recent studies suggest most cats carry papillomaviral DNA asymptomatically, meaning the virus is present on the skin without causing visible disease.⁵

Viral plaques are the mildest manifestation. They appear as flat, darkly pigmented, scaly patches on the skin, sometimes mistaken for a fungal infection or simple dermatitis. These are considered benign, but they sit at the beginning of a progression that can lead to worse outcomes. BISCs represent the next step along that path: the cells have become precancerous but remain confined to the outer layer of skin. If a BISC advances, it can become an invasive squamous cell carcinoma that penetrates deeper tissue. Not every viral plaque becomes a BISC, and not every BISC becomes invasive, but the progression from one to the next mirrors the stepwise development of cervical cancer in humans following persistent high-risk HPV infection.

FcaPV-2 and Cancer

Among the known feline types, FcaPV-2 draws the most concern. When researchers tested 18 BISC samples by quantitative PCR, 15 were positive for FcaPV-2, two were positive for FcaPV-4, and one tested negative for all feline papillomaviruses studied.⁶ A separate study using fluorescence in situ hybridization found FcaPV-2 DNA within about a third of BISC lesions, with the viral DNA sitting inside the nuclei of abnormal cells in the upper layers of the skin.⁷ Detection rates vary depending on the method used, but FcaPV-2 turns up far more consistently in BISCs than any other viral type.

The connection extends beyond precancerous lesions into frank malignancy. Squamous cell carcinoma is one of the most common skin cancers in cats, and mounting evidence points to papillomaviruses as a significant driver of at least a subset of these tumors.⁸ The picture is complicated by the fact that UV radiation is also a well-known cause of squamous cell carcinoma in cats, particularly on the ears, nose, and eyelids of white or lightly pigmented animals. Papillomavirus-driven tumors appear to be a distinct subset, though the two pathways can overlap.

The UV-Protected Skin Paradox

One of the clearest pieces of evidence for a viral role in feline skin cancer comes from comparing tumors in sun-exposed and sun-protected areas. When researchers looked at squamous cell carcinomas on UV-protected skin (areas covered by dense fur), papillomaviral DNA was present in about three-quarters of tumors, and a cellular marker called p16 was elevated in 84% of them. In UV-exposed skin tumors, those numbers dropped to roughly 42% and 40%, respectively.⁹

This makes intuitive sense. Squamous cell carcinomas in cats’ sun-exposed areas have long been attributed to UV damage, the same force that causes skin cancer in fair-skinned humans. But when a tumor develops on densely furred skin where UV exposure is minimal, something else has to be driving it. The frequent presence of FcaPV-2 DNA and elevated p16 in those tumors points strongly toward a viral cause. FcaPV-2 is thought to be the virus behind most viral plaques and BISCs, and the logical extension is that some of those lesions progress to invasive carcinoma in UV-protected sites.

How the Virus Mimics High-Risk Human HPV

The molecular mechanisms behind FcaPV-2 oncogenesis are strikingly familiar to anyone who has studied human HPV-driven cancers. Like its human counterparts, FcaPV-2 produces two key proteins, E6 and E7, that disrupt the cell’s normal tumor-suppression machinery. Laboratory studies showed that FcaPV-2’s E6 protein binds to feline p53, the “guardian of the genome” protein that normally triggers cell death when DNA is damaged. E6 recruits a cellular enzyme called E6AP to form a three-protein complex with p53, tagging p53 for destruction by the cell’s own protein-recycling system.¹⁰ This accelerated degradation of p53 is the same mechanism used by high-risk human HPV types 16 and 18.

Meanwhile, FcaPV-2’s E7 protein binds and degrades pRb, another critical tumor suppressor that normally keeps cell division in check. When E7 knocks pRb out of the picture, cells lose a major brake on proliferation. Intriguingly, research also found that each oncoprotein has secondary effects on the other’s usual target: E7 reduced p53 levels through an mRNA-level mechanism (distinct from E6’s protein-degradation approach), and E6 reduced pRb protein levels even though it did not physically bind pRb in pull-down assays.¹¹ The result is that both of the cell’s major safety nets get dismantled simultaneously, creating a permissive environment for uncontrolled growth.

The Oral Cancer Question

Feline oral squamous cell carcinoma (FOSCC) is the most common oral cancer in cats and carries a poor prognosis. Given the strong connection between human HPV and oropharyngeal cancer, researchers naturally wondered whether feline papillomaviruses play a similar role. The evidence here is mixed and more uncertain than for skin tumors.

A multicentric study testing 113 FOSCC samples for multiple viral types found FcaPV-2 in about 7.5% of samples, FcaPV-1 in 6.2%, and FcaPV-3 in 5.3%, with the other types at very low levels or absent entirely.¹² Prevalence also varied between geographic regions, with different rates in Italian versus Austrian samples. A separate study found FcaPV-2 DNA in about a third of FOSCCs and, more meaningfully, detected active viral gene expression (the E6E7 oncogenes) in half of those DNA-positive tumors. The researchers interpreted this as suggestive but not definitive proof of a viral role in a proportion of oral tumors.¹³

On the other side of the debate, an earlier study using p16 immunostaining and PCR failed to amplify papillomaviral DNA from any feline oral squamous cell carcinoma tested, concluding that the results did not support papillomaviruses as a significant cause of oral tumors in cats.¹⁴ These contradictory findings likely reflect differences in detection sensitivity, sample size, and geographic variation in viral prevalence. The current consensus, if it can be called that, is that FcaPV-2 is probably involved in some feline oral cancers but is not the dominant cause the way HPV 16 is in human oropharyngeal carcinoma. Other factors, including chronic inflammation and environmental carcinogens, likely play a larger role in most cases.

P16 as a Diagnostic and Prognostic Clue

In human medicine, overexpression of a protein called p16 serves as a reliable surrogate marker for HPV-driven tumors, particularly in the cervix and throat. Researchers have explored the same marker in cats. The logic is the same: when viral E7 protein knocks out pRb, the cell compensates by ramping up p16 production, so elevated p16 flags the viral pathway. A study of feline nasal planum squamous cell carcinomas found that cats with p16-positive tumors survived longer than those with p16-negative tumors, and the p16-positive group was more likely to harbor papillomaviral DNA. The authors proposed that p16 could serve as a useful prognostic indicator in these common feline cancers, and that the different survival times support the idea that p16-positive and p16-negative tumors have distinct causes.¹⁵

This parallels human oncology, where HPV-positive head-and-neck cancers tend to respond better to treatment and carry a more favorable prognosis than HPV-negative ones. If the same pattern holds broadly in cats, p16 staining could help veterinarians make more accurate predictions about a tumor’s behavior and guide treatment decisions. However, widespread routine p16 testing for feline tumors is not yet standard practice.

Feline Sarcoids and Cross-Species Infection

Not all papillomavirus-associated lesions in cats come from feline papillomaviruses. Feline sarcoids, which are firm, fibrous skin growths that tend to appear on the face and limbs, are caused by a bovine papillomavirus. The virus responsible has never been detected in non-sarcoid feline samples but has been found on the skin of cattle, and genomic analysis led researchers to propose classifying it as Bos taurus papillomavirus type 14 (BPV-14).¹⁶ This is a genuine cross-species infection: a cattle virus jumping to cats, likely through environmental contact. A similar situation occurs in horses, where bovine papillomaviruses cause equine sarcoids, a well-known veterinary problem. In cats, sarcoids are much rarer but follow the same pattern of cross-species viral transmission.

The existence of feline sarcoids raises an obvious question for cat owners: can the feline papillomaviruses spread to humans? Papillomaviruses are, as a rule, strongly host-restricted. Human HPV types do not productively infect cat cells, and feline papillomaviruses do not infect human tissue. No case of human infection with a feline papillomavirus has been documented. The bovine-to-cat jump seen in sarcoids is an exception that involves closely related host species and does not extend to humans. So while the molecular machinery of FcaPV-2 closely mirrors that of high-risk human HPV, the two viruses operate in separate biological worlds.

An Ancient Evolutionary Partnership

The relationship between papillomaviruses and cats stretches back millions of years. Phylogenetic analyses have shown that feline papillomavirus evolutionary trees mirror the branching pattern of their cat-family hosts, a hallmark of long-term co-speciation. One landmark study estimated the overall evolutionary rate of feline papillomaviruses at roughly two hundredths of a billionth of a nucleotide substitution per site per year, which is slow even by DNA virus standards and consistent with a virus that has been riding along with its hosts for millions of years of feline diversification.¹⁷

More recent discoveries have complicated this tidy picture. A papillomavirus isolated from the tree ocelot (a small wild cat in South America) provided evidence that not all feline papillomavirus lineages followed the co-speciation path. Instead, some lineages appear to have polyphyletic origins, meaning they arose independently more than once within the cat family, possibly through ancient host-switching events.¹⁸ Similarly, papillomaviruses found in caracals in South Africa revealed diverse viral lineages and hints of recombination, further suggesting that the evolutionary history includes both faithful co-divergence and occasional jumps between host species.¹⁹ The full picture is one of deep co-evolution punctuated by rare but significant cross-species events, which helps explain why some feline papillomaviruses are closely related to viruses in distantly related felids while others have no close feline relatives at all.

Why There Is No Feline HPV Vaccine Yet

Given the success of human HPV vaccines in preventing cervical cancer and genital warts, it is natural to wonder why no equivalent exists for cats. The short answer is that the veterinary market and the state of the science have not yet aligned. Human HPV vaccination is justified by the enormous burden of cervical cancer and the clear, well-characterized causal pathway from persistent infection to precancer to invasive disease over decades. In cats, the evidence connecting papillomavirus to cancer is strong and growing but still more fragmented. Not every squamous cell carcinoma is viral in origin, the proportion that is varies by body site, and the field lacks the kind of large-scale epidemiological data that drove human vaccine development. A 2021 review noted that vaccine development for feline papillomavirus disease has been discussed but remains in early conceptual stages.²⁰

There is also a practical challenge. Most cats appear to carry papillomaviral DNA without developing disease, and the factors that push an asymptomatic infection toward visible lesions or cancer are not fully understood. Immune suppression is thought to play a role: cats with compromised immune systems, whether from feline immunodeficiency virus, feline leukemia virus, or immunosuppressive medications, seem more prone to developing viral plaques and BISCs. But the precise cofactors and the timeline from infection to disease remain unclear. Without that clarity, designing a vaccine trial with measurable endpoints is difficult. For now, the best prevention strategy is the unglamorous combination of monitoring skin changes, minimizing unnecessary immunosuppression, and pursuing early biopsy of suspicious lesions, particularly in cats with pigmented, scaly plaques on furred skin.

What Cat Owners Should Watch For

Because most feline papillomavirus infections are silent, and because the progression from benign plaque to cancer can take months to years, early detection depends on owners and veterinarians noticing subtle skin changes. Viral plaques often appear as dark, thickened, crusty patches, sometimes with a greasy texture. They can occur anywhere on the body but are most noteworthy in areas with heavy fur cover, where UV radiation is not a plausible alternative explanation. Multiple plaques may appear simultaneously. In immunocompromised cats, plaques can be widespread.

A plaque that changes in appearance, grows rapidly, ulcerates, or becomes raised and nodular warrants a veterinary visit and likely a biopsy. BISCs can look clinically similar to benign plaques, and the distinction usually requires microscopic examination. The good news is that BISCs, while precancerous, are often slow to progress, and surgical removal at the in situ stage tends to be curative. The challenge is that some cats develop multiple BISCs in different locations, requiring ongoing monitoring even after one is removed. Squamous cell carcinomas that have become invasive carry a more serious prognosis and may require more aggressive treatment, including surgery and radiation, making early detection all the more worthwhile.