Abstract

The Channel Island fox (Urocyon littoralis) was listed as endangered under the Federal Endangered Species Act on March 5, 2004 due to serious declines in populations of four subspecies over the last decade.¹ One of the four listed subspecies, U. littoralis catalinae, is present on Santa Catalina Island, where the population declined precipitously and dramatically by approximately 90% in 1999. This decline was believed to be the result of an outbreak of canine distemper.⁵ Current population recovery efforts on Santa Catalina Island include a captive breeding program, and monitoring and vaccination of both captive and wild populations with a recombinant canarypox-vectored canine distemper vaccine (Purevax Ferret™, Merial, Inc., Athens, GA, USA). In 2001 and 2002, the vaccine was given intramuscularly to wild and captive foxes. Disadvantages of administering the vaccine by injection included: stress of capture and handling on the animals; potential for local or systemic reactions to the injected vaccine; costs for staff and staff safety concerns; and significant time delays between the initiation of the vaccination effort and achievement of vaccination of a significant portion of the population. Although antibody levels as measured by serum neutralization indicated that vaccine response occurred with intramuscular administration of the vaccine, the disadvantages of administering the vaccine by injection prompted us to investigate oral administration as an alternative.

Vaccine-laced bait has been used to effectively reduce labor costs, capture stress, and time required to accomplish vaccination in certain wildlife disease management efforts.^2-4,9 In 2003 we orally administered Purevax Ferret™ to 16 captive-raised juvenile island foxes. Two 1-ml vials of the vaccine were administered to each fox at approximately 16, 20, and 24 weeks of age by one of two different oral routes: 1) direct administration of the rehydrated vaccine solution into the oral cavity, and 2) injection of the vaccine into a food item fed directly to the fox. Group selection was determined randomly within each of six pens housing foxes. Blood samples were collected from foxes to determine distemper antibody titers at 1, 3, and 5 months post final vaccine administration (p.v.). Serum neutralization to measure antibody titers was conducted by the Cornell University Veterinary Diagnostic Laboratory. Foxes were sampled while still in captivity at 1 month p.v., and the 3- and 5-month p.v. samplings occurred after the juvenile foxes were released to the wild. One fox was subsequently removed from the study due to management considerations. All 15 foxes remaining in the study were captured for re-sampling at least once post-release. At 1 month p.v., 13/16 foxes (81.3%) showed measurable antibody response to the vaccine (>1:6). Mean antibody titers were statistically significantly higher in the direct administration group (p=0.003 student t test mean log₁₀). Two foxes had interfering substances that rendered the first antibody measurement invalid. Initial antibody titers achieved in our study were consistent with levels demonstrated to be protective in some vaccine challenge studies in species with similar sensitivity to canine distemper virus.^6-8 Measurement of antibodies in samples obtained at 3 and 5 months p.v. are underway, and antibody persistence in our two study groups is being evaluated and compared to previous years when the vaccine was given intramuscularly. Based on our initial findings, we believe direct oral administration of Purevax Ferret™ to be a viable option for vaccinating Channel Island foxes, but a better bait formulation may be necessary for food-based vaccination to be effective.

Literature Cited

1.  Coonan, T. J. 2001. Draft recovery plan for island foxes (Urocyon littoralis) on the Northern Channel Islands. Prepared for National Park Service.

2.  Foroutan P., M. I. Meltzer, K. A. Smith. 2002. Cost of distributing oral raccoon-variant rabies vaccine in Ohio: 1997–2000. J Am Vet Med Assoc. 220(1):27–32.

3.  Knobel, D. L., A Liebenberg, J. T. Du Toit. 2003. Seroconversion in captive African wild dogs (Lycaon pictus) following administration of a chicken head bait/SAG-2 oral rabies vaccine combination. Onderstepoort J Vet Res. 70(1): 73–77.

4.  Selhorst, T., H. H. Thulke, T. Muller. 2001. Cost-efficient vaccination of foxes (Vulpes vulpes) against rabies and the need for a new baiting strategy. Prev Vet Med. 51(1–2):95–109

5.  Timm, S. F., J. M. Stokely, T. B. Gehr, R. L. Peebles, and D. K. Garcelon. 2000. Investigation into the decline of island foxes on Santa Catalina Island. Prepared for the Institute for Wildlife Studies.

6.  Welter, J., J. Taylor, J. Tartaglia, E. Paoletti, and C. B. Stephenson. 1999. Mucosal vaccination with recombinant poxvirus vaccines protects ferrets against symptomatic CDV infection. Vaccine. 17: 308–318.

7.  Wilmsatt, J., M. T. Kay, K. E. Innes, M. Jessen, and J. K. Collins. 2001. Serological evaluation, efficacy and safety of a commercial modified-live canine distemper vaccine for immunization of the domestic ferret (Mustela putorius furo). Am. J. Vet. Res. 62:736–740.

8.  Wilmsatt, J., D. Biggins, K. E. Innes, B. Taylor, D. Garrell. 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.

9.  Vos, A. 2003. Oral vaccination against rabies and the behavioural ecology of the red fox (Vulpes vulpes). J Vet Med B Infect Dis Vet Public Health. 50(10): 477–83.