Of the 11 marine mammal facilities surveyed, 5 were located on the eastern (Atlantic) coast and 6 were located on the western (Pacific) coast of North America (Table 1). Survey informants who represented these facilities were staff veterinarians or veterinary technicians (55%), self-described facility directors (18%), or researchers and rehabilitation trainers (27%). Survey informants provided demographic and health information for 1,423 pinnipeds, representing 14 species (Table 1). Of these pinnipeds, 47% were California sea lions and 27% were harbor seals, and 84% of the animals were housed in facilities located along the Pacific coast (Table 1). Five species were represented on both coasts. Fifty-five percent of pinnipeds described were male, and 83% were <1 year of age.

Informants were asked to recall the approximate numbers of animals in which sealpox was clinically diagnosed during the previous year. If informants provided a range of case counts, the lower number was selected. For the 12-month period, an estimated 30 (2%) animals at the 11 facilities had sealpox; 25 diagnoses were presumptive (based on clinical suspicion) and 5 were laboratory confirmed (positive PCR or electron microscopy results). Demographic and health data were not available for 7 animals with presumptive sealpox; thus, these animals were not included in subsequent analyses, leaving a total of 23 infected pinnipeds at 9 centers for analysis of characteristics associated with sealpox virus infection. Individual animals from 4 species were identified as having sealpox: California sea lions (8), harbor seals (11), gray seals (3), and northern elephant seals (1) (Table 2). Sealpox was diagnosed upon arrival at a center for 5 (22%) animals (all wild), <5 weeks after arrival for 11 (48%) animals, and >5 weeks after arrival for 2 (9%) animals (Table 2). The timing of illness onset was independent of the animal’s geographic location, species, and age. Most (83%) sealpox was diagnosed in pups, but the prevalence of infection was equivalent for adults and pups (1.2% and 1.8%, respectively).

Of the ill animals, 9 (39%) were malnourished, 4 (17%) had concurrent illness, and 10 (44%) had injuries and were malnourished or had concurrent illness (Table 2). Those with concurrent illness died or were euthanized (including all adults in which sealpox was diagnosed), while most animals with malnutrition recovered (Table 2). Informants from 5 marine centers reported transmission of sealpox from infected animals to unhealthy convalescing pinnipeds at their facility, 4 reported transmissions to healthy pinnipeds, and 6 reported transmission among pups. Of the 9 facilities that housed infected animals, 4 reported isolating them to prevent transmission.

To identify factors that might be associated with transmission of sealpox virus in marine mammal facilities, we obtained information about disinfectant use in pens, the number of animals housed per pen, and other housing characteristics (Table 3). Individual facilities had 1 to >16 enclosures and housed <83 pinnipeds during the 12 months before completing the survey. All facilities used at least 1 type of disinfectant, and all reported cleaning pens at least 1× each week (Table 3). To assess whether medical screening and treatment practices might affect detection and prevention of sealpox, we obtained information about facility admission protocols for pinnipeds as well as laboratory and medical resources available at the facility. All facilities had quarantine or isolation enclosures for sick or newly admitted animals, and all facilities included a physical examination as part of their standard protocol for pinnipeds entering the facility. Of the 9 facilities that had animals with sealpox, 9 (100%) reported isolating newly admitted pinnipeds and collecting blood samples for pathogen screening; 4 (44%) also did fecal flotation and culture; and 2 (22%) did other tests, including, including urinalysis and radiography or ultrasound (Table 3). All facilities had veterinarians on site and used third-party diagnostic laboratories; 64% also had a veterinary diagnostic laboratory on site.

Overall, no significant association was found between sealpox infection and species, sex, or age in the study population (Table 2), and no significant associations were found at the facility level. The likelihood of a pinniped having sealpox was greater in facilities on the Atlantic coast (4% of animals) than the Pacific coast (1% of animals) (odds ratio 3.53; p = 0.002). However, this observation mainly results from case clusters at 2 facilities on the Atlantic coast. All of the ill animals were characterized as having been rescued or having been in rehabilitation (Table 1). All but 1 facility reported housing adults and pups together and housing different pinniped species together; there was no association with sealpox infection (Table 3). Of the 11 surveyed facilities, 9 (82%) cleaned the enclosures at least daily with bleach-based cleaning products (Table 3). No significant associations were found between type of disinfectant used and odds of sealpox infection. All facilities that housed infected animals reported cleaning enclosures at least daily.

None of the facility informants reported cases of sealpox infections among humans at the facility during the prior 12 months, but informants at 2 facilities reported cases of physician-diagnosed sealpox among workers in the previous 10 years. At both facilities, the affected persons were reported to have handled live animals with skin or oral lesions or both. Use of personal protective equipment (PPE) was reported at all facilities: 100% of respondents reported use of gloves; 91%, rain pants, overalls, or suits; and 9%, goggles and masks.

In addition to the survey of marine mammal rehabilitation facilities, we asked marine mammal workers attending a conference about their knowledge and experience with sealpox. Thirty-one conference attendees completed the survey. Of the 31 respondents, 17 (55%) reported observing pinnipeds affected with sealpox virus in rehabilitation facilities or in the wild, of which 9 were in North America, 5 in northern Europe, and 2 in New Zealand (1 location not specified). (In the United States, human sealpox virus infection is not a nationally reportable condition. However, as a rare infection, it would be considered notifiable in most states.) Of the 17 workers, 13 reported knowledge that sealpox virus can infect humans, and most (15/17) reported that they had learned this information from colleagues or educational material distributed at their workplace. Of the 31 respondents, 7 (23%) reported they had seen or known about a human case of sealpox: 2 reported that a colleague had received a diagnosis of sealpox, and 5 reported that they themselves had received a diagnosis of sealpox at some point during the past 15 years. Two of these 7 persons stated that their physician had prescribed tetracyclines to treat their infections. Tetracyclines are ineffective against sealpox infections; however, antimicrobial drugs are effective against a mycoplasma-associated infection, called seal finger, which is clinically similar to and can be confused with sealpox.

For sea lions entering rehabilitation facilities, a history of rehabilitation is a strong indicator of the risk for poxvirus lesions (14). In our survey, facility informants reported that 2% of the animals housed in the marine mammal facilities surveyed had laboratory-confirmed or presumptive sealpox during the preceding 12 months. The proportion of infected animals was higher in facilities on the Atlantic than Pacific coast; however, on balance, more animals were housed in rehabilitation facilities on the Pacific coast. California sea lions accounted for the majority of pinnipeds under observation and for the majority of infected animals. Most infected animals were pups and were male, a finding consistent with previous observations (1,14). Documented infections have typically been reported for young animals brought into rehabilitation environments, which may reflect increased susceptibility among juvenile animals, particularly those under stress (2). Malnutrition, a hallmark of rescued pups, seemed not to indicate a poor prognosis, whereas injury, older age, and concurrent illness did.

Approximately one fifth of infected animals arrived at the rehabilitation facility with symptoms of sealpox infection, and infection was observed within 5 weeks after arrival for half of the animals. We did not attempt to address whether underlying poor health status predisposes an animal to infection with sealpox virus or vice versa. However, 5 facility informants reported sealpox transmission in their facility to both unhealthy and healthy pinnipeds, suggesting that, in captivity, the disease can develop even in apparently healthy animals. The transmission dynamics of sealpox virus have not been well described, but transmission between pinnipeds is likely to occur during suckling; through other forms of skin-to-skin contact; or by fomites, which are of particular concern for captive animals. Further studies are needed to explain transmission dynamics.

Serosurveys suggest that sealpox virus is persistently infecting most wild California sea lions, and other species of pinnepeds may also be persistently infected with other sealpox species (23). Thus, for persons who rehabilitate animals, risks for zoonotic transmission of these agents might be appreciable. Vigilant adherence to quarantine and institutional hygiene practices, including the use of PPE by staff, likely serves to diminish risks for virus transmission to humans and may explain why reports of human infection with sealpox virus are rare (16,17). In our study, all marine mammal workers who knew that sealpox virus is zoonotic reported that they had learned this information from colleagues and educational material provided by their workplace, and all facilities reported that PPE (gloves, boots) were made available to all workers; however, some marine mammal workers indicated that PPE is rarely used when pinnipeds are handled in the wild. Sealpox is only 1 of many potential hazards associated with wildlife rehabilitation activities; workplace education programs should highlight the risk for zoonotic disease transmission from pinnipeds to marine mammal workers and the use of PPE when handling animals in the wild.