ABSTRACT. On August 2007, we encountered equine influenza epidemic by Florida sub-lineage strain (H3N8) in Japan Racing Association's facilities where 4142 racehorses in total were stabled. The number of new febrile cases sharply increased, but the occurrence was rapidly calmed down within 2 weeks. The morbidity rate in these facilities was 12.8% and the subclinical infection rate of healthy racehorses examined by rapid antigen detection tests was 19.4% at the early stage of epidemic. The serological studies along with the low morbidity rate and the existence of numbers of asymptomatically infected racehorses, suggested that the cross-reactivity of the antibodies provided by vaccination against the epidemic strain contributed to reducing the morbidity rate and duration of epidemic. KEY WORDS: equine influenza, racehorses, vaccine.J. Vet. Med. Sci. 70(6): 623-625, 2008 Equine influenza virus (EIV) is one of the most important respiratory pathogens of horses, due to its rapid spread among susceptible animals. Infected horses with EIV develop typical respiratory disorders including acute onset of pyrexia, nasal discharge, coughing and depression [10,12]. This viral infection has lead to severe economic loss to the horse industries, for example, in Hong Kong in 1992 [9] and in South Africa in 1986 [3], horseracing was obliged to be cancelled for several months. Also in Japan, from 1971 to 1972, the outbreak of EI was occurred and the horseracing was cancelled for 2 months [5]. Owing to extensive vaccination for horses after 1972, no EI occurrences had been reported in Japan. In recent years, since the EI occurrences by EIV which is classified into Florida sub-lineage diverged from American lineage were reported in some foreign countries [7,8], the Office International des Epizooties (OIE) recommends A/equine/Ohio/1/03-like strain classified into the same sub-lineage as vaccine strain (http://www.oie.int/ eng/Eq%20inf%20conc%20%20recs%202005.pdf). Strains currently contained in the Japanese inactivated whole vaccine are A/equine/La Plata/93 (H3N8 American lineage, La Plata/93), A/equine/Avesta/93 (H3N8 Eurasian lineage, Avesta/93), and A/equine/Newmarket/77 (H7N7). The Japanese vaccines against EIV have not contained the recommended strain yet. On August 2007, the authors met an epidemic of EI in the facilities of the Japan Racing Association (JRA), Miho Training Center (Miho TC, Ibaraki prefecture), Ritto Training Center (Ritto TC, Shiga prefecture), Sapporo Racecourse (Sapporo RC, Hokkaido prefecture), Hakodate Racecourse (Hakodate RC, Hokkaido prefecture) and Kokura Racecourse (Kokura RC, Fukuoka prefecture). Each facility stabled 1599, 1367, 494, 532 and 150 racehorses registered by JRA at the onset of the epidemic, respectively. All horses were stabled under high standards of management and veterinary care by JRA, and received booster vaccinations at intervals of six months following a primary vaccination in mandatory. All horses were lastly vaccinated for EI in May 2007. This note provides the overview of th...
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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