Abstract
The Hawaiian monk seal (Monachus schauinslandi) was listed as an endangered species in 1976. The population declined 60% from 1958 to 1992 and remained relatively stable from 1993 to 2000, but numbers began to decline again in 2001.2 The total population has been estimated at about 1300 seals. Known reasons for monk seal mortality and the lack of population growth over the last 2 decades include entanglement in marine debris, male aggression, shark predation, human disturbance, and malnutrition. Epidemiologic surveys since 1998 have not demonstrated disease to be a significant impediment to population recovery, although studies have implicated traumatic injuries and infectious diseases, such as parasitism and bacterial infection, as contributors to individual animal deaths.1 While limited data are available relative to the role of viral diseases in compromising monk seal health, the possible association of a morbillivirus infection with a mass mortality event in Mediterranean monk seals (Monachus monachus) in 1997 demonstrates the potential impact that a viral infection might have on an endangered population of animals.3,4
Serologic evidence for the existence of a herpesvirus infection in Hawaiian monk seals has recently been detected utilizing an ELISA assay developed to measure antibodies to phocine herpesvirus-1 (PhHV-1) in harbor seals (Phoca vitulina). Although the monk seal sera were positive for anti-herpesviral antibodies, these antibodies were unable to neutralize the PhHV-1 isolate in serum neutralization tests.
The goal of this study was to identify and characterize this putative monk seal herpesvirus in nasal swab samples collected from free-ranging and captive Hawaiian monk seals. Previously published degenerate primers were used to initially identify the novel sequence.5 All samples were then analyzed with a monk seal herpes-specific primer pair. This analysis identified a previously unknown gamma herpesviral molecular isolate in 20% (19/95) of the animals. The isolate was similar to gorilla rhadinovirus and porcine lymphotropic virus. This newly identified monk seal virus has not yet been associated with disease.
Acknowledgments
This work was supported by grants from the Marine Mammal Health and Stranding Program, Office of Protected Resources, National Marine Fisheries Service as well as The Marine Mammal Center and the UC Davis Wildlife Health Center. The authors wish to thank the many dedicated researchers from the Marine Mammal Research Program, Honolulu Laboratory, National Marine Fisheries Service for their technical support and help with collection of field samples and the U.S. Fish and Wildlife Service and the State of Hawaii Department of Land Natural Resources for their logistical support. Thanks also to Sea World of Texas for providing samples from the captive seals. We would also like to thank Jerry Saliki for providing Phocine herpesvirus-1 and -2 isolates from Atlantic harbor seals and Don King for providing the Otariine herpesvirus-1 isolate from a California sea lion for comparative purposes. Thanks to Ken Jackson for help with the phylogenetic analysis. Samples were collected under the authority of Marine Mammal Protection Act permit number 848-1135.
Literature Cited
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