Abstract
All families of the order Carnivora are susceptible to infection with canine distemper virus (CDV), a ubiquitous and potentially fatal disease.1,2 Domestic dogs are vaccinated with a modified live (ML) vaccine for protection against this disease. However, these ML vaccines have induced disease and death in several nondomestic carnivore species, including the highly endangered European mink (Mustela lutreola).3 Safer alternatives are inactivated virus vaccines, subunit vaccines, or recombinant vaccines. Recombinant vaccines have proven to be safe and efficacious in polecats (Mustela eversmanii), a species closely related to the European mink, and other carnivore species.4 However, the use of recombinant CDV vaccines is forbidden in the European Union, and monovalent inactivated vaccines are no longer commercially available. A safe and effective vaccination campaign is essential for protection of valuable and endangered susceptible species in zoos and breeding centers/reintroduction projects. The goal of this study was to evaluate and compare the humoral immunogenicity of a commercial recombinant CDV vaccine (Purevax™, Merial, Duluth, GA, USA) and an experimental immunostimulating complex CDV vaccine (CDV-ISCOM, Erasmus MC, Rotterdam, Netherlands) in European mink.
Previously unvaccinated captive European mink housed in a breeding and reintroduction center in Tallinn, Estonia were used for this study. Six mink were vaccinated with Purevax™ and six mink were vaccinated with CDV-ISCOM. As a negative control group, five mink were injected with a phosphate buffered saline solution. The mink were vaccinated three times intramuscularly at 3-week intervals. Blood was collected from the jugular vein prior to each vaccination. Postvaccinal blood samples were taken 3 weeks and 1 year, after the last vaccination. Serum antibody titers were determined by virus neutralization (VN) and ELISA tests.
Both types of CDV vaccine produced an increase in serum titer (booster effect) after the second and third vaccinations. Antibody titers were produced in all animals after three vaccinations. The mean VN antibody titer induced after three vaccinations with CDV-ISCOM was 20-fold higher than that produced by Purevax™ (1:1280 vs. 1:57). Mean antibody titers measured by ELISA followed the same trend but were higher. One year after the last vaccination, VN titers had declined, but were still detectable, with those after CDV-ISCOM vaccination being higher (1:160 vs. 1:56). In the Purevax™ group two animals did not have a detectable titer after 1 year. Control animals did not produce titers throughout the study. None of the animals showed clinical signs of CDV infection, or any other negative effect that could be attributed to vaccination.
This study demonstrates that the Purevax™ and CDV-ISCOM vaccines appear safe for European mink and induce a humoral immune response in this species as determined by VN and ELISA tests. The presence of a humoral immune response has been shown to be positively correlated with increased survival following challenge with CDV infection in other species and may be expected to offer protection for mink.4 In conclusion, this study suggests that while both vaccines induce a humoral response, the CDV-ISCOM vaccine protects European mink better against CDV infection because it induces higher antibody titers in this species. Further work will be conducted to determine the cellular immune response produced by both vaccines.
Literature Cited
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4. Wimsatt, J., D. Biggins, K. Innes, B. Taylor, and D. Garell. 2003. Evaluation of oral and subcutaneous delivery of an experimental canarypox recombinant canine distemper vaccine in the Siberian polecat (Mustela eversmanii). J Zoo Wildl Med. 34(1):25–35.