Antigenic Activity of Canine Enteric Coronavirus Strain "Rich" in Experiments with Rabbits, Ferrets and Guinea Pigs

Introduction. Canine enteric coronavirus is a widespread infection, especially dangerous for the puppies of up to 12 weeks old kept in shelters and breeding kennels. The causative agent Alphacoronavirus 1 has a high mutational variability. Foreign sources have repeatedly reported on the isolation and study of the new strains of canine coronavirus infection, including the pantropic ones, causing systemic pathology and death of animals. In this regard, the currently produced vaccines are not effective enough. The present research is intended to substantiate one of the solutions to the problem. The aim of the work is to evaluate the antigenic potential of the canine enteric coronavirus strain “Rich” in terms of its reliability for being included in the combined vaccines against canine viral diseases.
Materials and Methods. A purified suspension culture of the canine enteric coronavirus strain “Rich” with the infectivity titers 4.0±0.25 lg TCID₅₀/cm³ (TCID — Tissue Culture Infectious Dose) was used in the work. Antigenic properties were studied in laboratory animals: rabbits, ferrets and guinea pigs. The virus neutralising antibody titers for the canine enteric coronavirus in the blood serum of the experimental animals was determined by a neutralisation test using the “standard” viral dose of 100 TCID₅₀/cm³ in the feline kidney cell culture. The material for the test was obtained from the Cell Culture Bank of the Federal Centre for Animal Health.
Results. In animals initially seronegative to the virus, an increase in the CCoV virus-neutralising antibodies (VNA) titers has been recorded 7 days after a single injection of the suspension of the canine enteric coronavirus strain “Rich”. Over the time, the level has been increasing and has reached its maximum value on the 21st day. The mean value in the group of rabbits has been 4.08±0.36 log₂ SN₅₀, ferrets — 3.72±0.35 log₂ SN₅₀ and 3.77±0.63 log₂ SN₅₀, guinea pigs — 4.12±0.34 log₂ SN₅₀. Then the values of the virus neutralising antibody titers have decreased, but remained at a fairly high level for 35 days (observation time). At the same time, the physiological state of the animals has not changed.
Discussion and Conclusion. In general, the results of the experiments are consistent with the conclusions of the other authors. New data has been obtained by studying the antigenic properties of the strain in ferrets. The strain injected into them has demonstrated the clearly expressed antigenic activity and did not cause a general or local pathological response of the body. The “Rich” is promising for further study and can be included in the combined vaccines against canine and other animal viral diseases.

1. Evermann JF, Abbott JR, Han S. Canine Coronavirus-Associated Puppy Mortality without Evidence of Concurrent Canine Parvovirus Infection. Journal of Veterinary Diagnostic Investigation. 2005;17(6):610–614. https://doi.org/10.1177/104063870501700618

2. Pratelli A, Tempesta M, Roperto FP, Sagazio P, Carmichael L, Buonavoglia C. Fatal Coronavirus Infection in Puppies Following Canine Parvovirus 2b Infection. Journal of Veterinary Diagnostic Investigation. 1999;11(6):550–553. https://doi.org/10.1177/104063879901100615

3. Decaro N, Buonavoglia C. An Update on Canine Coronaviruses: Viral Evolution and Pathobiology. Veterinary Microbiology. 2008;132(3–4):221–234. https://doi.org/10.1016/j.vetmic.2008.06.007

4. Decaro N, Camero M, Greco G, Zizzo N, Tinelli A, Campolo M, et al. Canine Distemper and Related Diseases: Report of a Severe Outbreak in a Kennel. New Microbiologica. 2004;27(2):177–181.

5. Sanchez-Morgado JM, Poynter S, Morris TH. Molecular Characterization of a Virulent Canine Coronavirus BGF Strain. Virus Research. 2004;104(1):27–31. https://doi.org/10.1016/j.virusres.2004.02.038

6. Escutenaire S, Isaksson M, Renström LH, Klingeborn B, Buonavoglia C, Berg M, et al. Characterization of Divergent and Atypical Canine Coronaviruses from Sweden. Archives of Virology. 2007;152(8):1507–1514. https://doi.org/10.1007/s00705-007-0986-1

7. Buonavoglia C, Decaro N, Martella V, Elia G. Campolo M, Desario C, et al. Canine Coronavirus Highly Pathogenic for Dogs. Emerging Infectious Diseases. 2006;12(3):492–494. https://doi.org/10.3201/eid1203.050839

8. Decaro N, Martella V, Elia G, Campolo M, Desario C, Cirone F, et al. Molecular Characterisation of the Virulent Canine Coronavirus CB/05 Strain. Virus Research. 2007;125(1):54–60. https://doi.org/10.1016/j.virusres.2006.12.006

9. Pratelli A, Elia G, Martella V, Tinelli A, Decaro N, Marsilio F, et al. M Gene Evolution of Canine Coronavirus in Naturally Infected Dogs. Veterinary Record. 2002;151(25):758–761.

10. Licitra BN, Duhamel GE, Whittaker GR. Canine Enteric Coronaviruses: Emerging Viral Pathogens with Distinct Recombinant Spike Proteins. Viruses. 2014;6(8):3363–3376. https://doi.org/10.3390/v6083363

11. Pratelli A. High-Cell-Passage Canine Coronavirus Vaccine Providing Sterilising Immunity. Journal of Small Animal Practice. 2007;48(10):574–578. https://doi.org/10.1111/j.1748-5827.2007.00416.x

12. Olshanskaya AA. Biological Properties and Diagnosis of Canine Coronavirus Enteritis. Extended Abstract of Cand.Sci. (Biology) Dissertation. Moscow; 1997. 28 p. (In Russ.).