Widespread neonatal infection with phocid herpesvirus 1 in free-ranging and stranded grey seals Halichoerus grypus

Phocid herpesvirus 1 (PhHV-1) is known to infect grey seals Halichoerus grypus but little is known about its pathogenicity or true prevalence in this species. To investigate the prevalence of and risk factors associated with PHV-1 infection, nasal swabs were collected from grey seal pups and yearlings on the Isle of May, a well-studied grey seal breeding colony, and from stranded grey seal pups submitted to a rehabilitation centre. PhHV-1 nucleic acids were detected in nasal swabs from 58% (52/90) of live free-ranging grey seal pups, 62% (18/29) of live stranded grey seal pups and 28% (5/18) of live free-ranging yearlings, suggesting recrudescence in the latter. Location within the colony, pup body mass and stranding were determined to be risk factors for shedding PhHV-1 in live seal pups with a significantly higher prevalence of PhHV-1 in pups born on the tidal boulder beach when compared to other sites; a significantly positive correlation of PhHV-1 shedding and pup body mass and a higher prevalence in stranded grey seal pups compared to their free-ranging conspecifics. The prevalence of PhHV1 in dead pups on the Isle of May was 56% (27/48) with a positive PhHV-1 PCR status significantly associated with hepatic necrosis (p = 0.01), thymic atrophy (p < 0.001) and buccal ulceration (p = 0.027). Results indicate that PhHV1 was widespread in the pups in the Isle of May grey seal breeding colony.