Modelling the spatial dynamics of parapoxvirus disease in red and grey squirrels: a possible cause of the decline in the red squirrel in the UK?

An inactivated canine distemper vaccine with adjuvant and a modified-live virus (MLV) vaccine were evaluated using black-footed ferret (Mustegla nigripes) x Siberian polecat (Mustela eversmanni) hybrids us surrogates for endangered black-footed ferrets. For comparative purposes, we also vaccinated domestic ferrets (Mustela putorius furo) with the MLV vaccine. Response to vaccination was measured by clinical observation, hematology, dynamics of serum virus neutralizing antibodies, and challenge with virulent canine distemper virus. No clinical signs attributable to the vaccines were observed. Transient leukopenia occurred in hybrid ferrets that received MLV vaccine and there was marked lymphopenia for approximately 52 days post-vaccination. Lymphopenia was present for approximately 21 days in domestic ferrets vaccinated with MLV vaccine. Neutralizing antibodies against canine distemper virus were detected 14 days post-vaccination in hybrids receiving MLV vaccine and most titers were > 1:1024 for the 791 days of the study. Antibody titers in hybrids vaccinated with the inactivated vaccine were significantly lower. All eight hybrid ferrets that received MLV vaccine survived challenge with virulent canine distemper virus without clinical disease. However, one of seven hybrids vaccinated with the inactivated vaccine developed canine distemper and was euthanized; two other hybrids became clinically ill but survived. The MLV vaccine may be useful in prevention of canine distemper in black-footed ferrets, but until additional studies of efficacy and safety are completed, use of the inactivated vaccine is appropriate.