Abstract
The domestic ferret is highly susceptible to canine distemper virus (CDV). Several available CDV vaccines have been implicated in causing deleterious side-effects in this species. The purpose of the present study was to assess the safety and efficacy of Galaxy® D (modified-live CDV vaccine, Schering-Plough Animal Health Inc.) for CDV vaccination in the domestic ferret.
Methods
Sixteen neutered male ferrets were randomly assigned to one of two treatment groups and either vaccinated subcutaneously with Galaxy® D (vaccinates) or injected similarly with saline (controls) at 16 and 20 weeks of age. Live virus virulent strain CDV challenge (Synder Hill Strain, NVSL, Ames IA, instilled intranasally and orally) was performed 3 weeks after the second vaccination. Sign development was scored by a study blinded observer, and body weights were collected at regular intervals throughout the study. Blood serology (serum neutralization, SN) samples were drawn before study, prior to vaccination and challenge, and at 10, 15, and 21 days after challenge. Blood samples for PCR were drawn 5 days following the first vaccination, and at 5, 10, 15, and 21 days after challenge.
Results
No significant sign differences were observed in the vaccinates in response to vaccination, whereas, CDV-induced signs, including weight loss (days 7 and 14, p<0.0001) were noted in all the controls following challenge. In response to challenge, vaccinate survival was 100% (8/8); nonvaccinate survival was 0% (0/8). PCR analysis of blood samples 5 days after vaccination detected vaccine strain CDV in one first-time vaccinate (12.5%). Following challenge, CDV was detected by PCR in the blood of all controls (100%, 8/8) from 5 days until death; in contrast, detection was made in two (25%) vaccinates (two primers) at 10 days post-challenge. Median SN titers went from 1:2 before the first vaccination, to 1:384 before the second the vaccination, to 1:2048 before the challenge. Corresponding titers in the controls were 1:2, 1:8, and 1:4. At necropsy, PCR detected CDV in fresh (all four primers) or formalin-fixed (two primers) tissues (lung, bladder, brain) from infected controls dying of CDV, and in none of the vaccinates.
Conclusions
Although not approved by the U.S. Department of Agriculture for this application, Galaxy® D given twice subcutaneously to domestic ferrets starting at 4 months of age appeared safe and protective against CDV virulent strain challenge. PCR was a useful method to detect CDV infection from fresh blood and tissue samples, and from formalin fixed tissues.
Acknowledgments
Partial support was provided by Schering-Plough Animal Health Inc. We thank Ms. Jane Carmen, Jill Steege, and Rick Heimbichner for expert technical assistance.