Epidemic of Equine Influenza among Vaccinated Racehorses in Japan in 2007

Abstract

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...

Epidemiological and virological findings during multiple outbreaks of equine influenza in South America in 2012

“…Subsequent evolution within the Florida sublineage has resulted in the emergence of two distinct clades, designated as Florida clade 1 and Florida clade 2 11, 12. Florida clade 1 viruses are endemic in the USA but have also caused outbreaks in South Africa,13 Japan,14 Australia 15 and Europe 11, 16, 17, 18, 19. Florida clade 2 viruses have predominated in Europe but have also been the cause of major outbreaks of EI in China,20 Mongolia 21 and India 22…”

Antibody Responses Induced by Japanese Whole inactivated Vaccines against Equine Influenza Virus (H3N8) Belonging to Florida Sublineage Clade2

“…Avesta93 and La Plata93 were introduced into the vaccines in 2004 and 1996, respectively [8,13]. Ibaraki07 was isolated from a horse during the equine influenza epidemic in Japan in 2007 and classified as Fc1 [3,22]. Ibaraki07 was introduced into the Japanese vaccines in October 2009.…”

Equine influenza

“…To 2007 αναφέρεται για πρώτη φορά η νόσος σε ιπποειδή στην Αυστραλία. Επιδημιολογική έρευνα που ακο λούθησε κατέδειξε ως αιτία τη μη τήρηση μέτρων καραντίνας σε νεοεισερχόμενους ίππους από την Ιαπωνία (Anon, 2008, Callinan, 2008, παρά το γεγονός ότι στην Ιαπωνία δεν είχε παρατηρηθεί η νόσος τα τελευταία 35 χρόνια πριν το 2007 (Bryant et al, 2009, Yamanaka et al, 2008.…”