Feline leukaemia vaccine protection against viral latency.

Seventeen cats, which were previously vaccinated with a subunit, feline leukaemia vaccine (Leukocell) and subsequently challenged with virulent feline leukaemia virus (FeLV), were tested at 2 to 4 years postchallenge for reactivation of latent FeLV infections. Administration of weekly doses of methylprednisolone induced significant decreases in lymphocyte numbers, but did not reactivate virus in bone marrow cultures from 15 cats in vivo or in vitro. These cats were observed to be neither persistently or latently viraemic prior to corticosteroid administration. The results of this study indicate that the vaccine is effective in affording significant protection against latent FeLV infections, even after severe immunosuppression. This finding, coupled with previously published results indicating protection against persistent viraemia and tumour formation, makes this vaccine highly effective in protecting against FeLV infections and associated disease.