Vetnews | Oktober 2024 38 « BACK TO CONTENTS Papillomaviruses are non-enveloped, double-stranded DNA viruses in the family Papillomaviridae. Papillomaviruses [PV] are a group of viruses that cause benign tumours, known as papillomas or warts, in various animals. These warts can appear on different body parts, including the skin, mucous membranes, and in some cases, the ocular structures. Papillomavirus (PV) can infect and propagate in the cutaneous and mucosal epithelial cells of a wide variety of animal species with a high species specificity and are antigenically distinct. Although three bovine papillomaviruses (BPV 1, BPV 2, and BPV 13) have been demonstrated to cross-infect the cutaneous fibroblastic cells in equines, the majority of PV’s only infect the epithelium and cause associated lesions. To date, there are more than 50 genera, and at least 318 types of PV, which affect over 54 different species. Two forms of papillomaviruses (oral form and conjunctival form) have been associated with causing papillomas involving the canine eye and adnexa. Oral papillomas, which are usually found in young animals, result from infection with a canine papillomavirus-1 (CPV1) (previously known as canine oral papillomavirus [COPV]), and the solitary skin lesions of older animals result from infection with cutaneous papillomaviruses (CPV-1, -2, -6, and -7). The CPV-1 may, in addition to causing oral papillomas, produce lesions on the eyelids, conjunctiva, and cornea. Papillomas develop 4–8 weeks after infection with CPV-1, and they usually regress within 4–8 weeks after their development as T-cells migrate into the papilloma from a cell-mediated immunity response. Despite the spontaneous regression of most viral papillomas, the ocular forms may not regress. Ocular viral papillomas have been reported in dogs as old as 9 years of age. Importantly, however, conjunctival squamous papillomas have been described in older dogs and have not been associated with papillomaviruses Once the PV comes into contact with a mucocutaneous epithelium, the presence of microabrasions or open wounds allows infection of basal cells, resulting in proliferation and the production of small numbers of circular PV DNA copies (episomes) within the cell. The infective virons are only formed when the epithelial cells undergo keratinization differentiation. Over time the characteristic lesion is then noted. Papilloma’s in Dogs: In dogs, oral papillomas are caused by CPV-1 and are common in young dogs. Papillomavirus infection can cause single or multiple epithelial plaques and papillomas in a variety of locations on the skin, including the mucosa and mucocutaneous membranes of the oral cavity, conjunctiva and cornea, lips, penis, and vulva. The lesions seen can include oral papillomatosis, cutaneous papillomas and canine viral pigmented plaques. Historically, a conjunctival form of papilloma, that is distinct from the large cauliflower lesions of viral papillomas, has been described; it typically manifests as a solitary lesion on the dorsal to lateral bulbar conjunctiva, in proximity to the limbus, and is often pigmented, slightly nodular, and has fronds on the surface, and in these instances, may appear similar to nonviral conjunctival squamous papillomas. Most lesions in older animals are solitary, but multiple lesions may also develop. The overwhelming majority of canine oral papillomas spontaneously regress and surgical excision is rarely necessary. Regression is due to the development of a cell-mediated immune response. In experimentally induced papillomas, resolution typically occurs within 8 weeks. However, resolution of natural papillomas appears to be more variable, with resolution taking up to 12 months in some dogs. The growth period from the first sign of tumour until the first sign of regression lasted four to eight weeks in 65 per cent of the dogs and nine to 21 weeks in 21 per cent of the dogs in one study. Puppies are immune to reinfection after spontaneous regression has occurred. The mechanism leading to the spontaneous regression of COPV-induced papillomas in the dog is unknown. In our experience at Jhb Animal Eye Hospital, spontaneous regression seems to be longer compared to what has been described for oral lesions and for this reason, most lesions do require surgical removal. The Veterinary Journal 225 (2017) 23–31 Eye-related papillomatosis is less common but can appear around the eyes, on the eyelids, or conjunctiva. Papillomas represent about 10%–20% of lid tumours in dogs, with tarsal adenoma being the most common. Regulars I Ophthalmology Column Eye-Related Papillomatosis in Dogs, Cats, Sheep, Goats and Cattle Dr Anthony Goodhead Specialist Veterinary Ophthalmologist Johannesburg and Cape Animal Eye Hospitals www.animaleyehospital.co.za
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