ABSTRACT. Equine coronavirus (ECoV) outbreaks have occurred three times at Obihiro Racecourse in Hokkaido, Japan. The third ECoV outbreak occurred between late February and early April 2012. The main clinical signs of affected horses were anorexia, pyrexia and leucopenia; gastrointestinal disease was observed in about 10% of affected horses. Two ECoV strains were isolated from diarrheal samples. All paired sera (9/9) collected from febrile horses showed seroconversion by neutralization test. Sequence and phylogenetic analysis of the ECoV isolated showed that putative amino acid sequences in S and N genes were highly conserved among ECoV strains. In contrast, sequences of the region coding 4.7kDa non-structural protein (p4.7) differed among the strains. Because of the diversity of the p4.7 region, this region should be useful for epidemiological investigation of ECoV.

Recently, outbreaks associated with equine coronavirus (ECoV) have occurred in Japan and the United States. While ECoV is likely to be pathogenic to horses, it has not been shown that experimental inoculation of horses with ECoV produces clinical signs of disease. In this study, we inoculated three Japanese draft horses with an ECoV-positive diarrheic fecal sample to confirm infection after inoculation and to investigate the clinical course and virus shedding patterns of ECoV. Virus neutralization tests showed that all three horses became infected with ECoV. Two of the three horses developed clinical signs similar to those observed during ECoV outbreaks, including fever, anorexia, and gastrointestinal dysfunction. All horses excreted a large amount of virus into their feces for more than 9 days after inoculation regardless of the presence or absence of clinical signs, which suggests that feces are an important source of ECoV infection. ECoV was also detected in nasal swabs from all horses, suggesting that respiratory transmission of ECoV may occur. Both symptomatic horses developed viremia, while the asymptomatic horse did not. White blood cell counts and serum amyloid A concentrations changed relative to the clinical condition of the inoculated horses; these may be useful markers for monitoring the clinical status of horses infected with ECoV. This is the first report of induction of clinical signs of ECoV infection in horses by experimental inoculation. These clinical and virological findings should aid further investigation of the pathogenesis of ECoV.

An outbreak of Getah virus infection occurred among racehorses in Japan during September and October 2014. Of 49 febrile horses tested by reverse transcription PCR, 25 were positive for Getah virus. Viruses detected in 2014 were phylogenetically different from the virus isolated in Japan in 1978.

ABSTRACT. An equine herpesvirus type 1 (EHV-1) mutant, gE, defective in glycoprotein E (gE) was evaluated as a modified live virus (MLV) vaccine. Colostrum-deprived Thoroughbred foals inoculated intranasally (i.n.) or intramuscularly (i.m.) with gE did not exhibit any clinical signs of respiratory disease except for a mild nasal discharge in 1 i.n. inoculated foal on Days 1 and 3 post-infection. In contrast, the intranasal inoculation of foals with the revertant of gE resulted in biphasic pyrexia, mucopurulent nasal discharge and swelling of submandibular lymph nodes. These results indicated that gE plays an important role as regards EHV-1 virulence in horses. The ability of gE to protect against wild type EHV-1 challenge infection was assessed using i.m. vaccinated foals. Foals inoculated twice i.m. with 10 5 or 10 6 plaque-forming units (pfu) of gE at an interval of 3 weeks exhibited no clinical evidence of local inflammation, respiratory disease or deleterious systemic responses. Remarkable increases in SN antibody titer to EHV-1 were observed in all vaccinated foals after the 2nd inoculation with gE. Following a wild type EHV-1 challenge infection, vaccinated foals showed milder clinical symptoms than foals vaccinated with a placebo. Specifically, 1 of 3 foals vaccinated with 10 6 pfu of gE exhibited no clinical symptoms other than a mild nasal discharge for 1 day. Additionally, the virus load of nasal shedding and viremia were reduced by vaccination. These results suggest that gE would be a good candidate as an MLV vaccine.KEY WORDS: attenuated live vaccine, EHV-1, gE.

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