Investigations on course and outcome of phocine distemper virus infection in harbour seals (Phoca vitulina) exposed to polychlorinated biphenyls. Virological and serological investigations.

The influence of polychlorinated biphenyls (PCBs) on phocine distemper virus (PDV) infections in harbour seals (Phoca vitulina) was studied. Six out of ten seals had been conditioned with a defined mixture of PCB-congeners for several weeks. Following exposure to the cell culture-propagated PDV isolate 2558/Han 88 the complete clinical picture of "1988 seal plague" was provoked in all ten seals inoculated. Four out of six PCB-conditioned seals and two out of four seals not loaded with PCBs succumbed to the infection within three weeks post inoculation. With regard to the clinical course, duration of cell-associated viremia, PDV-antigen distribution in tissues of fatally infected seals and the humoral immune response to PDV no differences between PCB-loaded and unloaded seals were recognized. Evidence was obtained that the pathogenesis of experimental PDV-infection in harbour seals shares some features with those of canine distemper in terrestrial carnivores. In contrast, however, to experimental distemper infection of gnotobiotic dogs prompt development of high titres of PDV-specific IgG did not correlate with recovery from infection.

Morbillivirus infections of seals during the 1988 epidemic in the Bay of Heligoland: III. Transmission studies of cell culture-propagated phocine distemper virus in harbour seals (Phoca vitulina) and a grey seal (Halichoerus grypus): clinical, virological and serological results.

Eight harbour seals (Phoca vitulina), two of them seronegative, six seropositive against PDV and a seronegative grey seal (Halichoerus grypus) were exposed to a low doses of a cell culture-propagated phocine distemper virus isolate (PDV 2558/Han 88). An intranasal route of inoculation was chosen. Clinical signs, resembling those of 1988's seal disease and seroconversion were observed in both seronegative harbour seals. One of them succumbed to the infection. The virus was not transmitted to another susceptible harbour seal which served as in-contact animal. Virus could be recovered from leucocytes of the diseased seals. Viremia was also present in a seropositive harbour seal that developed mild clinical signs; other seropositive seals were protected from clinical disease. The grey seal showed seroconversion upon inoculation, but did not develop any signs of disease. The humoral immune response of the seals plainly discriminated between homologous (PDV) and heterologous (canine distemper virus, CDV) virus as shown by virus neutralization tests and an antibody-binding assay (PLA).

Herpesvirus in harbour seals (Phoca vitulina): transmission in homologous host.

In the Norddeich orphanage seals about four to five months of age were exposed intranasally and by contact to a phocine herpesvirus which originated from a young seal in this station. Virus excretion by the nasal route was observed in two animals on day 2 and 15 post inoculation, respectively. Production of neutralizing antibodies was detected one week after exposure. The antibody titre range was approximately tenfold higher in the inoculated seals than in animals of the contact group. The seals did not become seriously sick.

Morbillivirus infection among seals (Phoca vitulina) during the 1988 epidemic in the Bay of Heligoland. II. Serogological investigations reflecting a previous phocine distemper epidemic in a seal orphanage.

Of 57 seals hospitalized in the Norddeich Orphanage, 37 (65%) had died until 22nd of August, 1988, when the first collection of blood samples from the survivors commenced. All the sera including those obtained at a later date from the remaining animals had invariably higher neutralizing antibody titres against a phocine distemper virus (PDV) isolate than against canine distemper virus (CDV). The difference of mean titres was calculated to be more than 1.5 x log10 serum dilution. Peak titres demonstrated by a direct neutralization peroxidase-linked antibody (NPLA) assay reached 1/90,000. Attempts to isolate PDV in seal kidney cell cultures from heparinized blood samples collected from convalescent animals were not successful. From the increase in antibody titre following the last fatal case it was concluded that the devastating epidemic sweeping through the Norddeich Orphanage was primarily due to phocine distemper.