Prevalence of canine coronavirus (CCoV) in dog in Japan: detection of CCoV RNA and retrospective serological analysis

TAKANO, Tomomi; YAMASHITA, Saya; MURATA-OHKUBO, Michiko; SATOH, Kumi; DOKI, Tomoyoshi; HOHDATSU, Tsutomu

Reverse 5′-ttaaggattaaaaacatattcta-3′ report, we investigated the correlation between the age and CCoV infection in dogs with diarrhea symptoms. In these dogs, the CCoV infection rate was higher in dogs younger than one year old compared to older dogs (46.4%, of less than 1 year, and 31.8% of over 1 year, respectively; Table 2 ). We retrospectively investigated the seroprevalence of CCoV-I in dogs in Japan during 1998 to 2006. Serum samples from 695 dogs collected from various regions throughout Japan were examined for the prevalence of antibodies to FCoV-I and CCoV-II by neutralization test. These samples were submitted to veterinary clinics in Japan: the Hokkaido region (Hokkaido); the Tohoku region (Aomori, Akita, Miyagi, Yamagata and Fukushima); the Kanto region (Tochigi, Ibaraki, Gunma, Saitama, Chiba, Kanagawa and Tokyo); the Chubu region (Niigata, Nagano, Toyama, Ishikawa, Fukui, Shizuoka, Yamanashi, Aichi and Gifu); the Kinki region (Osaka, Kyoto, Nara, Shiga, Mie and Hyogo); the Chugoku region (Okayama, Hiroshima, Tottori and Yamaguchi); the Shikoku region (Tokushima, Ehime and Kochi); and the Kyushu region (Fukuoka, Nagasaki, Kumamoto, Oita and Miyazaki). Of the 695 serum samples used, 405 were collected from dogs with an unclear vaccination history. The remaining 290 samples were collected from dogs previously treated with CCoV vaccine. Neutralization test was performed by using modified method based on the report described by Takano et al. [14] . Briefly, Serial two-fold dilutions of the test sera were mixed with an equal volume of FCoV-I KU-2 strain (isolated in our laboratory) or CCoV-II 1-71 strain (supplied by Dr. E. Takahashi of the University of Tokyo) suspension containing approximately 200 TCID 50 /100 µl, and mixtures were incubated at 37°C for 60 min. Each mixture was inoculated into fcwf-4 cells in 96-well microplates, followed by incubation at 37°C for 3 days in an atmosphere of 5% CO 2 . The antibody titer was expressed as a recipro-cal of the highest dilution of the test sera that completely inhibited the cytopathic effect. 540 (77.7%) of the 695 sera were positive for neutralizing anti-FCoV-I antibodies, and the neutralizing antibody titers ranged from 1:5 to 1:80. Neutralizing anti-FCoV-I antibodies were detectable in sera collected in 1998 (positive rate: 86.7%, 52 of 60 serum samples). The antibody-positive rate tended to decrease after 2001.