SEALPOX and cetacean POX

DEBRA BOURNE

Wildlife Information Network, Twycross Zoo — East Midland Zoological Society, Atherstone, UK

The viruses causing sealpox are parapoxviruses, although they are not yet accepted in virus taxonomy.

SEALPOX

Sealpox lesions were first reported in captive Californian sea lions (Zalophus californicus) in Canada in 1969, and the ultrastructural morphology of the virus was described the following year⁽³³⁾. Sealpox is generally a self- limiting disease characterized by localized skin lesions, but some severe cases have been seen. Within Europe, pox virus lesions have been described in grey seals (Halichoerus grypus) from the Netherlands¹-³⁴) and the UK^(35-38) and harbour seals (Phoca vitulina) from the German North Sea⁽³⁹⁾.

Lesions vary from a few localized lesions on the skin of the head and neck, one or two digits, or the oral cavity, to multiple lesions along the mucocutaneous border or the lips, and multiple lesions, becoming confluent, along much of the ventral neck and body. Small lesions heal spontaneously in about 6 weeks, whereas in extensive cases, skin swellings develop to circumscribed lesions 1.5—

2.5 cm diameter and become suppurative. Oral lesions in a severe case started as ulcers, which, as they started healing, were replaced by roundish granulomatous lesions about

1.5 cm diameter⁽³⁶⁾. Histologically, the s tratum corneum shows hyperkeratosis and parakeratosis, and the s tratus spinosum shows hypertrophy, hyperplasia, cytoplasmic vacuolation and, in degenerating cells, large eosinophilic intracytoplasmic inclusions, mainly at the margins of lesions. The underlying dermis is infiltrated by neutrophils, with fibroblastic hyperplasia also evident.

Diagnosis is initially based on the clinical appearance of the lesions and on histopathological characteristics as described above. In most cases, the virus involved has been tentatively identified as a parapoxvirus, based on appear­ance from electron microscopy studies. In one case, both parapoxvirus-like and orthopoxvirus-like particles were seen and an orthopoxvirus was isolated⁽³⁴⁾; in another case, calicivirus particles were detected alongside typical parapox viruses. Parapoxvirus-specific antibodies were detected in sera of harbour and grey seals from the UK and the Neth­erlands, ringed seal (Phoca hispida) from the Netherlands, Baikal seal (Phoca siberica) from Lake Baikal, Russia, and grey and harbour seals from Canada⁽³⁸⁾. In recent years, partial genetic characterization has confirmed a parapox­virus, distinct from parapoxviruses of ruminants, in Euro­pean seals, Antarctic seals and in Pacific and Atlantic pinnipeds from the coasts of North America^(39,40).

Seal parapoxvirus infection is a potential zoonosis. In one outbreak in grey seals in Canada, two handlers developed lesions on their fingers similar to ‘milker’s nodules’, which can occur with other parapoxvirus infec­tions in humans; the lesions were self-limiting, although recurrent over several months in one individual¹-⁴¹).

CETACEANPOX

Poxvirus infections of a variety of cetaceans result in lesions of the skin, which are usually referred to as ‘tattoo lesions’. These have been seen in cetaceans worldwide, generally as an incidental finding, and have occasionally been described in cetaceans in European waters. Tattoo and paisley (print­like) lesions, similar to those confirmed as poxvirus infec­tions in other cetaceans, were described as incidental findings in five of 41 harbour porpoises (Phocoena phoc- oena) found on British coasts. In the tattoo lesions, a dark line about 1 mm wide enclosed an area, slightly depressed and sometimes containing small punctiform or linear black ulcers, while the paisley lesions involved several con­centric dark lines with normal-appearing skin between the lines.