Immune responses of the common seal (Phoca vitulina) to canine distemper antigens during an outbreak of phocid distemper viral infection

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Abstract
In 1988, there was a marked increase in the mortality rate of the common seal (Phoca vitulina) in European waters which was shown to be associated with a canine distemper‐like virus (CDV), recently named Phocid Distemper Virus (Cosbyet al., 1988). Investigations were carried out to determine the ability of common seals to respond immunologically and to determine the levels of antibody produced. Common seal immunoglobulins were purified, analysed and shown to be similar to those of other mammals. A simple immunoassay to measure seal antibodies to CDV was developed and showed striking differences between the susceptible seals (low levels of antibodies) and the surviving common seals (high amounts of anti‐distemper antibodies). Similar results were obtained with a neutralization test currently used to measure antibody titres to canine distemper virus in the dog. The adult common seals had high antibody titres and may be protected for future years, whereas the younger seals did not develop high levels of antibodies. This may be because either the younger seals had not encountered the virus or had not developed effective immunity.