Preliminary Experimental Canarypox-Vectored Recombinant Canine Distemper Vaccine Evaluation in the Siberian Polecat (Mustela eversmanii)
Mustelids and (primarily) other members of the Carnivora are highly susceptible to canine distemper virus (CDV) infection, a ubiquitous disease affecting susceptible captive and wild populations throughout the world. The endangered black-footed ferret (BFF, Mustela nigripes) is exquisitely sensitive to canine distemper, and a safe and effective vaccination strategy would be central to BFF reintroduction, and to protect other species at risk of contracting CDV-induced disease. An experimental canarypox recombinant subunit vaccine for eventual application in BFF and other susceptible species was evaluated in a captive-raised group of Siberian polecats (SP; M. eversmanii), believed to be the closest living relative to the BFF.
The purpose of the present study was to test the efficacy of an experimental canarypox vectored recombinant CDV subunit vaccine (ReCDV) for oral and parenteral administration and to determine its safety and efficacy via these routes.
SP with defined pedigrees were studied; their progenitors were collected from Inner Mongolia. ReCDV was administered at three (104.5, 105.0, 105.5) dose levels subcutaneously over the back, or by spraying (105.5, 108) into the oropharynx (orally). In all cases, two doses of reconstituted (1 ml) vaccine were delivered 4 weeks apart, followed by live virus challenge 3 weeks after the second vaccination. Based on preliminary data, the challenge consisted of Synder Hill strain CDV NVSL (#18-90) injected intraperitoneally at a dose four times the concentration shown to induce 100% mortality in SP previously. Clinical signs were observed daily, and weights were obtained weekly, then biweekly during the challenge period.
ReCDV at the highest oral dose induced an 83.3% (5/6) survival rate following live challenge, as compared to 0% (0/6) in the controls.
This study indicates the potential efficacy of oral vaccine delivery. Results presented here suggest that further studies are needed to evaluate the safety and efficacy of vectored recombinant vaccines in highly susceptible species, and especially in those species where CDV modified-live vaccination has precipitated disease. The potential to use such vaccines in the field in appropriate baits must be further explored.