Phocine Distemper Virus in Seals | CDC EID

EID Journal Home > Volume 17, Number 2–February 2011

Volume 17, Number 2–February 2011
Research
Phocine Distemper Virus in Seals, East Coast, United States, 2006
J.A. Philip Earle,1 Mary M. Melia,1 Nadine V. Doherty, Ole Nielsen, and S. Louise Cosby


Author affiliations: Queen's University Belfast, Belfast, UK (J.A.P. Earle, M.M. Melia, N.V. Doherty, S.L. Cosby); and Department of

Suggested citation for this article

Abstract
In 2006 and 2007, elevated numbers of deaths among seals, constituting an unusual mortality event, occurred off the coasts of Maine and Massachusetts, United States. We isolated a virus from seal tissue and confirmed it as phocine distemper virus (PDV). We compared the viral hemagglutinin, phosphoprotein, and fusion (F) and matrix (M) protein gene sequences with those of viruses from the 1988 and 2002 PDV epizootics. The virus showed highest similarity with a PDV 1988 Netherlands virus, which raises the possibility that the 2006 isolate from the United States might have emerged independently from 2002 PDVs and that multiple lineages of PDV might be circulating among enzootically infected North American seals. Evidence from comparison of sequences derived from different tissues suggested that mutations in the F and M genes occur in brain tissue that are not present in lung, liver, or blood, which suggests virus persistence in the central nervous system.

In 1988, harbor seals (Phoca vitulina) and gray seals (Halichoerus grypus) died in large numbers off the coast of northern Europe (1). A virus was first isolated in April 1988, when widespread abortions and deaths among harbor seals were reported in the Kattegat area between Denmark and Sweden. The infection spread to the North, Wadden, and Baltic seas, killing 17,000–20,000 seals in northwestern Europe in 8 months. The virus subsequently was classified as a species of the genus Morbillivirus (family Paramyxoviridae) (2,3), Phocine distemper virus (PDV). The virus is believed to have originated in harp seals in which the infection is enzootic (4). Migrations of harp seals into the North Sea may have initiated the epizootic in harbor seals. Gray seals in the northeastern Atlantic Ocean also were infected, but disease was not as severe as in harbor seals (5).

A more recent outbreak occurred in Europe in 2002 (6). An estimated 30,000 harbor and gray seals died during this epizootic (7,8). The origin of this second epizootic 14 years after the first remains unknown. PDV may have jumped species into terrestrial carnivores, particularly mink, and reinfected seals (9), but this hypothesis remains unproven. Phylogenetic analysis of the hemagglutin (H) genes of PDV, together with those of other morbilliviruses, suggests that the reemergent 2002 PDV is more closely related to a putative recent ancestral PDV than to the 1988 isolates (10). Millions of seals of various species inhabit the waters surrounding North America; populations of most species are believed to be stable or increasing, and no epizootics on the scale of those reported in Europe have been reported. PDV disease in the United States was first reported in harbor seals on the east coast during the winter of 1991–92 (11), and serologic testing of gray and harbor seals suggested that a PDV-like strain or strains were circulating enzootically in the region (12). This circulation was attributed to an increased number of harbor seals (mainly immature animals) overwintering in southern New England (13). During the spring of 2006, deaths among seals (harbor, gray, and hooded) also increased along the coasts of Maine and Massachusetts. This increase was considered an unusual mortality event. Both dead and sick seals appeared nonemaciated. Live-stranded seals were weak and had generalized body tremors and spasms. Affected seals were taken to the Marine Science Education and Research Center (University of New England, Biddeford, ME, USA); investigations indicated that the pathologic changes were consistent with morbillivirus infection. Recent advances in virus isolation and genetic sequencing methods have provided us with better insight into PDV epizootiology in Europe and in North America.

full-text:
Phocine Distemper Virus in Seals | CDC EID


Suggested Citation for this Article
Earle JAP, Melia MM, Doherty NV, Nielsen O, Cosby SL. Phocine distemper virus in seals, east coast, United States, 2006. Emerg Infect Dis [serial on the Internet]. 2011 Feb [date cited]. http://www.cdc.gov/EID/content/17/2/215.htm
DOI: 10.3201/eid1702.100190



1These authors contributed equally to this article.


Comments to the Authors
Please use the form below to submit correspondence to the authors or contact them at the following address:

S. Louise Cosby, Centre for Infection and Immunity, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast Medical Biology Centre, 97 Lisburn Rd, Belfast BT9 7BL, Northern Ireland, UK; email: l.cosby@qub.ac.uk