Transition of Akabane virus genogroups and its association with changes in the nature of disease in Japan

Abstract

Akabane virus (AKAV) is teratogenic to the foetus of domestic ruminants and causes a significant reproduction loss in cattle in Japan. In several past epizootics in cattle, AKAV was also associated with post-natal encephalomyelitis, mainly in calves and young stock. Previously analysed AKAV isolates in East Asia form two major clusters, genogroups I and II, with isolates involved in encephalomyelitis belonging mainly to the former. Between 2007 and 2013, AKAV epizootics were regularly observed in Japan during the summer/autumn season, and abnormal deliveries and post-natal encephalomyelitis caused by the virus in cattle were reported. During this period, 30 AKAV isolates were obtained from diseased and sentinel cattle, a piglet and Culicoides biting midges throughout Japan and were subjected to genetic comparison and phylogenetic analysis with previous isolates. In 2007, 2011 and 2013, AKAV belonging to genogroup I was identified in the central nervous systems of calves showing neurological disorders. Notably, a total of 165 cases of bovine encephalomyelitis were reported in 2011 and the isolated viruses from affected animals shared high genetic identities with a South Korean isolate that was associated with a large outbreak in 2010, suggesting some epidemiological linkage between these epizootics. Epizootics of genogroup II were observed in 2008 and 2010, but bovine post-natal encephalomyelitis cases rarely occurred. Our findings suggest that the frequent incursion of genogroup I isolates has increased the frequency of post-natal encephalomyelitis cases in Japan in recent years. Infection by genogroup I virus was also identified in piglets with neurological disorders or congenital malformations in 2011 and 2013. The aetiological role of AKAV in pigs should be elucidated in the future.

Endemic and Emerging Arboviruses in Domestic Ruminants in East Asia

“…Stillbirths and congenital malformations of neonate lambs caused by AKAV were observed in northern Japan between late 1985 and early 1986 (63). The isolation of AKAV from Culicoides biting midges, cattle, and a piglet has also been successful (64)(65)(66)(67). In 1984, AKAV was isolated from a postnatally infected calf with encephalitis during a small outbreak in Japan; it was a suspected causative agent (68).…”

“…Outbreaks of encephalomyelitis caused by postnatal AKAV infection occurred in 2006 and 2011 with 180 and 165 deaths, respectively (67,69). The AKAVs isolated in Japan since 1959 are clustered into two genogroups (I and II) (67,70).…”

“…Outbreaks of encephalomyelitis caused by postnatal AKAV infection occurred in 2006 and 2011 with 180 and 165 deaths, respectively (67,69). The AKAVs isolated in Japan since 1959 are clustered into two genogroups (I and II) (67,70). Genogroup I AKAVs have frequently been detected and/or isolated from affected cattle with encephalomyelitis (67,69).…”

“…The AKAVs isolated in Japan since 1959 are clustered into two genogroups (I and II) (67,70). Genogroup I AKAVs have frequently been detected and/or isolated from affected cattle with encephalomyelitis (67,69). These isolates probably have high neurotropic and/or neurovirulence and cause the neurological disorders in cattle.…”

“…Recent monitoring in Japan revealed that the frequent incursion of genogroup I AKAVs increased the number of postnatal encephalitis cases (65). There have been repeated epidemics of Akabane disease including both in utero and postnatal infections in Japan (52,67).…”