Abstract
Modified live virus vaccines against canine distemper virus (CDV) have induced disease and mortality in several highly endangered carnivores, including the African wild dog (Lycaon pictus). The goal of our study was to determine the safety and efficacy of two alternative vaccines in African wild dogs: an experimental subunit vaccine (immunostimulating complex, CDV-ISCOM, Erasmus MC, Rotterdam, The Netherlands) and a recombinant vaccine (Purevax™, Merial, Duluth, Georgia 30096 USA).
We vaccinated 13 animals in the Netherlands with CDV-ISCOM, and 13 in Tanzania with Purevax™. The vaccine was administered three times with a 3-week interval between each administration (1 ml, IM). Antibody titres to CDV were measured by enzyme-linked immunosorbent assay (ELISA) and virus neutralization (VN) in serum samples collected prior to each vaccination and 1 year post vaccination. Based on published data of CDV infection in domestic dogs, we considered a VN or ELISA titer of 80 or higher to be protective.
Neither vaccine produced any adverse reactions. One year post vaccination, the percentage of animals with protective titres was higher in the Purevax™ group (85% by ELISA, 39% by VN) than in the ISCOM group (69% by ELISA, 8% by VN). Surprisingly, the mean titer in the Purevax™ group was higher than in the ISCOM group by VN (63 versus 3), but lower by ELISA (109 versus 246).
Overall, these results indicate that both vaccines are safe, and that the Purevax™ vaccine may be more efficacious in African wild dogs than the ISCOM vaccine, although a substantial percentage of animals in both groups no longer had protective titres 1 year post vaccination. Titres following ISCOM vaccination were lower than those found in other non-domestic species.1 Reasons for this finding, and the discrepancies between VN and ELISA titres, remain unclear.
Acknowledgments
Our sincere gratitude for their help and support goes to: Ministry of Natural Resources & Tourism, Government of the United Republic of Tanzania.; Tony Fitzjohn, Lucy Fitzjohn, and the keepers of the African wild dogs in Mkomazi Game Reserve, Tanzania; and Daphne Valk and the keepers of the African wild dogs in Artis (Amsterdam Zoo).
Literature Cited
1. Philippa, J., T. Maran, M. van de Bildt, T. Kuiken, W. Schaftenaar, and A. Osterhaus. 2005. Humoral immune response to novel canine distemper vaccines in European mink (Mustela lutreola). Proc. Am. Assoc. Zoo Vet. Annu. Meet. Pp. 88–89.