Sealpox Virus in Marine Mammal Rehabilitation Facilities, North America, 2007–2009

Amira A. Roess, Rebecca Levine, Laura Barth, Benjamin Monroe, Darin Carroll, Inger Damon, and Mary Reynolds

Author affiliations: Centers for Disease Control and Prevention, Atlanta, Georgia, USA

Abstract

Sealpox, a zoonotic disease affecting pinnipeds (seals and sea lions), can occur among captive and convalescing animals. We surveyed 1 worker each from 11 marine mammal centers and interviewed 31 other marine mammal workers to ascertain their knowledge of and experience with sealpox virus and to identify factors associated with sealpox virus outbreaks among pinnipeds in marine rehabilitation facilities. Demographic and health data were obtained for 1,423 pinnipeds at the 11 facilities. Among the 23 animals in which sealpox was clinically diagnosed, 4 arrived at the facility ill, 11 became ill <5 weeks after arrival, and 2 became ill >5 weeks after arrival; the timing of illness onset was unknown for 6 animals. Most infections occurred in pinnipeds <1 year of age. Nine affected animals were malnourished; 4 had additional illnesses. Sealpox had also occurred among workers at 2 facilities. Sealpox is a noteworthy zoonosis of rehabilitating convalescing pinnipeds; workplace education can help to minimize risks for human infection.

Sealpox is a zoonotic disease of seals and sea lions (pinnipeds) and can be a complication of animals undergoing rehabilitation (1–4). The virus has been confirmed in free-ranging pinnipeds in the northern and southern Atlantic and Pacific Oceans (5,6), and infections have been observed in animals off the coast of Queen Maud’s Land, Antarctica (7). Sea lionpox virus is taxonomically and genetically distinct from other sealpox viruses found in Pacific Ocean pinnipeds (8); however, for convenience, hereafter we will refer to sea lionpox virus as sealpox virus.

Eight pinniped species are known to be susceptible to infection with sealpox viruses: Halichoerus grypus (gray seals), Phoca vitulina (harbor seals), P. groenlandica (harp seals), Callorhinus ursinus (northern fur seals), Mirounga angustirostris (northern elephant seals), Zalophus californianus (California sea lions), Eumetopias jubatus (steller sea lions), and Otaria flavescens (South American sea lions) (9–13). Many of the reported infections have been in young animals brought into rehabilitation environments (1,11), but infections have also been observed among animals in colonies undergoing exogenous stress (pollution, food scarcity, other underlying infection) and, on occasion, in otherwise seemingly healthy adults. Sealpox virus can spread easily among confined animals and can increase the costs and length of rehabilitation. Studies conducted in pinniped rehabilitation centers have suggested that underlying health conditions and a history of veterinary care are risk factors for sealpox virus infection among California sea lions (1,14).

Animals infected with sealpox virus typically show development of firm skin nodules (1–3 cm) on the head, neck, and thorax. Solitary clusters of nodules may also be found on the abdomen, flippers, and mucosa or oral cavity (6,13). The nodules frequently are inflamed or necrotic but usually heal spontaneously within a few weeks, leaving a slightly raised, gray, furless scar. Illness levels can be substantial, but death rates generally are low except among juveniles, for which infections can interfere with feeding (1,2,14). The transmission dynamics of sealpox virus have not been thoroughly investigated, but virus transmission is thought to occur directly by skin-to-skin contact.

Sealpox viruses are tentatively classified in the genus Parapoxvirus (15), which comprises multiple species of virus that can infect humans. Other members of this genus—namely, orf virus, pseudocowpox virus, and bovine papular stomatitis virus—commonly infect domestic ruminants and pose a minor occupational hazard to producers of sheep, goat, and cattle. The typical manifestations of infection in humans with any of these agents, including sealpox virus, are similar, usually culminating in a single nodular lesion with a diameter of ≈3 mm–1 cm. The nodule is often painful and evolves slowly over the course of several weeks. Infected persons may also briefly experience systemic signs and symptoms (fever, myalgia, fatigue) during the initial stages of lesion formation.

Sealpox virus is likely transmitted to humans when broken skin comes into contact with virus shed from lesions (skin or oral) on infected pinnipeds. Two epidemiologically linked and 1 molecularly confirmed case of sealpox virus infection in marine mammal handlers have been reported (16,17). In each case, the handler reported cutting himself while handling pinnipeds that had lesions indicative of sealpox virus infection. Although few sealpox virus infections in humans have been reported, and risks to marine mammal workers remain undefined, data indicate that ≈50% of marine mammal handlers have been injured by a marine mammal (18,19). The prevalence of human sealpox virus infections may therefore be underestimated.
Since the Marine Mammal Protection Act was enacted in 1972, researchers have documented sizable increases in the abundance of animals of several pinniped species in North America (20,21). Moreover, the number of live-stranded pinnipeds brought to rehabilitation facilities in the United States since the early 1970s has steadily increased over an order of magnitude and now represents hundreds of animals each year (22). Thus, compared with 40 years ago, today more opportunities exist for encounters between humans and convalescing pinnipeds.

To better understand the risks for sealpox virus infection in humans, we conducted a study of marine mammal workers at 11 marine mammal centers with rehabilitation capacity for species in North American waters; the objectives of the study were to ascertain the workers’ knowledge of and experience with sealpox virus and to identify factors associated with sealpox virus outbreaks among pinnipeds in rehabilitation centers. In addition, we also performed a survey of 31 marine mammal workers attending a professional conference to learn about their knowledge of and experience with sealpox infection in humans and animals.

Suggested citation for this article: Roess AA, Levine RS, Barth L, Monroe BP, Carroll DS, Damon IK, et al. Sealpox virus in marine mammal rehabilitation facilities, North America, 2007–2009 [serial on the Internet]. Emerg Infect Dis. 2011 Dec [date cited]. http://dx.doi.org/10.3201/eid1712.101945