| Papilloma viruses are small, double-stranded DNA viruses of the Papovaviridae family. Some mammals have several distinct papilloma viruses—humans have >20; cattle, 6; dogs, 3; and rabbits, 2. Different papilloma viruses often have considerable species, site, and histologic specificity. The virus is transmitted by direct contact, fomites, and possibly by insects. Papillomas have been reported in all domestic animals, birds, and fish. Multiple papillomas (papillomatosis) of
skin or mucosal surfaces generally are seen in younger animals and are usually caused by viruses. Papillomatosis is most common in cattle, horses, and dogs. Single papillomas are more frequent in older animals, but they may not always be caused by viral infection. |
| When lesions are multiple, they may be sufficiently characteristic to confirm the diagnosis; however, there are many simulants of warts, and a definitive diagnosis requires identification of the virus or its cytopathic effects on individual cells—a change known as koilocytic atypia or koilocytosis. |
| In cattle, warts commonly are found on the head, neck, and shoulders, and occasionally on the back and abdomen. The extent and duration of the lesions depend on the type of virus, area affected, and degree of susceptibility. Warts appear ~2 mo after exposure and may last ≥1 yr. Papillomatosis becomes a herd problem when a large group of young, susceptible cattle become infected. Immunity usually develops 3-4 wk after initial infection, but papillomatosis occasionally recurs,
probably due to loss of immunity. |
| Although most warts appear as epidermal proliferations that have a keratotic surface resembling a cauliflower (verruca vulgaris), some bovine papilloma viruses (bovine papilloma types 1 and 2) involve dermal fibroblasts and keratinocytes and appear as a papulonodule with a warty surface. Such fibropapillomas may involve the venereal regions where they can cause pain, disfigurement, infection of the penis of young bulls, and
dystocia when the vaginal mucosa of heifers is affected. |
| A form of persistent cutaneous papillomatosis with smaller numbers of papillomas may be seen in herds of older cattle. A bovine papilloma virus has been demonstrated in bladder tumors associated with bracken fern ingestion (
Bracken Fern Poisoning : Introduction) and in upper GI tract papillomas of cattle in Scotland. It is believed that the papilloma virus acts as a co-carcinogen. When bovine papilloma virus type 1 or 2 is injected into the skin of horses, a dermal tumor similar to
equine sarcoid develops. |
|
In horses, small, scattered papillomas develop on the nose, lips, eyelids, distal legs, penis, vulva, mammary glands, and inner surfaces of the pinnae, often secondary to mild abrasions. They can be a herd problem, especially when young horses are kept together, but regress in a few months, as a foal’s immune system matures. When they develop in older horses, they often persist for >1 yr. So-called aural plaques are also thought to be a flat
form of papilloma (verruca planum). Equine papillomas are disfiguring but benign. They need to be distinguished from verrucous equine sarcoid (
Soft-tissue Sarcomas). |
| In dogs, 3 clinical presentations of canine papilloma virus infection have been described. The first is
canine mucous membrane papillomatosis, which primarily affects young dogs. It is characterized by the presence of multiple warts on oral mucous membranes from lips to (occasionally) the esophagus and on the conjunctival mucous membranes and adjacent haired skin. When the oral cavity is severely affected, there is interference with mastication and swallowing. A viral etiology has been clearly established for these lesions. The second presentation is
cutaneous papillomas, which are indistinguishable from the warts that develop on or around mucous membranes. However, they are more frequently solitary and develop on older dogs. Cocker Spaniels and Kerry Blue Terriers may be predisposed. A definitive viral etiology has not been established, and lesions may be confused with cutaneous tags. Recently, a syndrome characterized by papillomatosis of one or more footpads has been described. Clinically, lesions appear as
multiple, raised keratin horns. A viral etiology has been suggested but not proven. The third presentation is
cutaneous inverted papillomas, which have more in common clinically with intracutaneous cornifying epitheliomas. In this disease of young, mature dogs, lesions most commonly develop on the ventral abdomen where they appear as raised papulonodules with a keratotic center. Infrequently, viral papillomas in dogs may progress to invasive squamous cell carcinomas. |
| In cats, papilloma virus infection appears most commonly as a multicentric squamous cell carcinoma (
Squamous Cell Carcinomas). The typical warty lesions associated with papilloma virus infection in most species are not present. Papillomas may affect the skin of goats, and infection on the teats has been reported to induce malignant transformation. In sheep, papillomas are rare and most commonly appear as fibropapillomas. In pigs, they are very rare and when present are
identified as solitary or multiple lesions on the face or genitalia. For discussion of papillomatosis in rabbits, see
Papillomatosis . |
| A cutaneous fibroma occurs in white-tailed, black-tailed, and mule deer, and in antelope, moose, and caribou. It is caused by a papilloma virus that resembles a bovine papilloma virus and is found only in the epithelium that covers the tumors. |
| Infectious papillomatosis is a self-limiting disease, although the duration of warts varies considerably. A variety of treatments have been advocated without agreement on efficacy. Surgical removal is recommended if the warts are sufficiently objectionable. However, because surgery in the early growing stage of warts may lead to recurrence and stimulation of growth, the warts should be removed when near their maximum size or when regressing. Affected animals may be isolated from
susceptible ones, but with the long incubation period, many are likely to have been exposed before the problem is recognized. |
| Vaccines are of some value as a preventive but are of little value in treating cattle that already have lesions. Because wart viruses are mostly species-specific, there is no merit in using a vaccine derived from one species in another. |
| When the disease is a herd problem, it can be controlled by vaccination with a suspension of ground wart tissue in which the virus has been killed with formalin. Autogenous vaccines may be more effective than those commercially available. It may be necessary to begin vaccination in calves as early as 4-6 wk of age with a dose of ~0.4 mL intradermally given at two sites. The vaccination is repeated in 4-6 wk and at 1 yr of age. Immunity develops in a few weeks but is unrelated to
whatever mechanism is involved in spontaneous regression. If the animal was exposed to the virus before vaccination, immunity may develop too late to prevent warts. A vaccination program must be in effect for ~3-6 mo before its preventive value will be evident. Vaccination should be continued for ≥1 yr after the last wart disappears because the premises may still be contaminated. Stalls, stanchions, and other inert materials can be disinfected by fumigating with formaldehyde. |
;)