Tissue distribution of phocine herpesvirus-1 (PhHV-1) in infected harbour seals (Phoca vitulina) from the central Californian coast and a comparison of diagnostic methods.

The polymerase chain reaction (PCR) was used to determine the tissue distribution of phocine herpesvirus-1 (PhHV-1) DNA in 20 stranded Pacific harbour seals (17 pups and three seals older than one year) that died during rehabilitation. The aim was to begin to define stages of infection and to investigate the relation between the presence of PhHV-1 in tissues, histological lesions and serology. PhHV-1 DNA was detected in a wide range of tissues from 10/17 pups and 3/3 subadults or adults. Different clinical patterns emerged from the examination of ante- and post-mortem samples. These patterns probably represented pups with active PhHV-1 infection, pups recovering from infection, and older harbour seals with chronic, reactivated infection. As PhHV-1 DNA was detected in tissues in the absence of typical histological lesions in seven seals and in the absence of PhHV-1 specific antibodies in four seals, it is clear that both histological examination and serology underestimate the presence of infection. These results showed that infection can occur in the absence of obvious disease and that seroconversion may be associated with clinical recovery.