Genetic Characteristics of Canine Adenovirus Type 2 Detected in Wild Raccoon Dogs (Nyctereutes procyonoides) in Korea (2017–2020)

SIMPLE SUMMARY: Adenovirus infection in animals occurs worldwide, and effective protection for pets is achieved through vaccination. Adenovirus vaccination in wild animals is rare, except in the case of rescue, treatment, and return to the wild. This study aimed to investigate the most prevalent canine adenovirus strains in Korean wild raccoon dogs, sequence the entire viral genome, and analyze the genetic characteristics in comparison with the adenovirus strains prevalent worldwide. We isolated one canine adenovirus type 2 (CAdV-2) and sequenced and analyzed its entire gene (CAdV-2/18Ra-54). This strain was found to have a high similarity with the Toronto A26/61 strain, which is widely used in vaccines, suggesting that pet vaccination can cause disease transmission and infection in wild animals. Therefore, further studies on the safety of the vaccine are needed. These studies monitor the epidemiology of CAdV-2 infection and contribute to the understanding of the genetic evolution of CAdV-2 in Korea and the development of new vaccines. ABSTRACT: Adenovirus has been detected in a wide range of hosts like dogs, foxes, horses, bats, avian animals, and raccoon dogs. Canine adenoviruses with two serotypes host mammals and are members of the mastadenovirus family. Canine adenovirus type 1 (CAdV-1) and canine adenovirus type 2 (CAdV-2) cause infectious canine hepatitis and infectious bronchial disease, respectively. In this study, we investigated the prevalence of CAdV-1 and 2 in wild Nyctereutes procyonoides in Korea in 2017–2020 from 414 tissue samples, including the liver, kidney, lung, and intestine, collected from 105 raccoon dog carcasses. Only CAdV-2 was detected in two raccoon dogs, whereas CAdV-1 was not detected. Tissue samples from raccoon dogs were screened for CAdV-1 and CAdV-2 using conventional PCR. Adenovirus was successfully isolated from PCR positive samples using the Vero cell line, and the full-length gene sequence of the isolated viruses was obtained through 5’ and 3’ rapid amplification of cDNA ends (RACE). The major genes of the isolated CAdV-2/18Ra54 and CAdV-2/18Ra-65 strains showed the closest relationship with that of the CAdV-2 Toronto A26/61 strain isolated from Canada in 1976. There is no large mutation between CAdV-2, which is prevalent worldwide, and CAdV-2, which is prevalent in wild animals in Korea. In addition, it is still spreading and causing infections. The Toronto A26/61 strain, which showed the most similarity to CAdV-2/18Ra-54, was likely transmitted to wild animals through vaccinated companion animals, suggesting that further research is needed on safety measures surrounding animal vaccination. This study provides information on the genetic characteristics and prevalence of canine adenovirus in domestic wild animals and provides a better understanding of canine adenovirus.