Epidemiology of a phocine distemper virus outbreak along the North Atlantic coast of the United States

Due to an increase in pinniped strandings with consistent pathological findings throughout the North Atlantic coast of the United States during the summer and fall of 2006, an unusual mortal- ity event (UME) was declared by the National Oceanic and Atmospheric Administration's (NOAA) National Marine Fisheries Service (NMFS) on 20 October 2006. The goals of this investigation were to describe the magnitude and duration of the peak in mortalities involved in the UME and to evaluate associations with potential causative agents. Seal strandings during the UME were compared to historical strandings in the area to characterize the epidemiologic pat- terns of the UME. Temporal increases in phocine distemper virus (PDV) prevalence as detected by serology and polymerase chain reaction (PCR) were significantly correlated with increased seal stranding frequency. During July to October 2006, there was a significant spatial and tempo- ral cluster of PDV positive seals centered near Cape Ann, Massachusetts. Our findings provide evidence that PDV infections increased in harbor seals along the North Atlantic coast of the U.S. in 2006, and PDV likely played a role in a UME that involved harbor seals (Phoca vitulina), harp seals Phoca groenlandica), hooded seals (Cystophora cristata), and gray seals (Halichoerus grypus).