Monitoring for bovine arboviruses in the most southwestern islands in Japan between 1994 and 2014.

BACKGROUND: In Japan, epizootic arboviral infections have severely impacted the livestock industry for a long period. Akabane, Aino, Chuzan, bovine ephemeral fever and Ibaraki viruses have repeatedly caused epizootic abnormal births and febrile illness in the cattle population. In addition, Peaton, Sathuperi, Shamonda and D'Aguilar viruses and epizootic hemorrhagic virus serotype 7 have recently emerged in Japan and are also considered to be involved in abnormal births in cattle. The above-mentioned viruses are hypothesized to circulate in tropical and subtropical Asia year round and to be introduced to temperate East Asia by long-distance aerial dispersal of infected vectors. To watch for arbovirus incursion and assess the possibility of its early warning, monitoring for arboviruses was conducted in the Yaeyama Islands, located at the most southwestern area of Japan, between 1994 and 2014. RESULTS: Blood sampling was conducted once a year, in the autumn, in 40 to 60 healthy cattle from the Yaeyama Islands. Blood samples were tested for arboviruses. A total of 33 arboviruses including Akabane, Peaton, Chuzan, D' Aguilar, Bunyip Creek, Batai and epizootic hemorrhagic viruses were isolated from bovine blood samples. Serological surveillance for the bovine arboviruses associated with cattle diseases in young cattle (ages 6-12 months: had only been alive for one summer) clearly showed their frequent incursion into the Yaeyama Islands. In some cases, the arbovirus incursions could be detected in the Yaeyama Islands prior to their spread to mainland Japan. CONCLUSIONS: We showed that long-term surveillance in the Yaeyama Islands could estimate the activity of bovine arboviruses in neighboring regions and may provide a useful early warning for likely arbovirus infections in Japan. The findings in this study could contribute to the planning of prevention and control for bovine arbovirus infections in Japan and cooperative efforts among neighboring countries in East Asia.

Epidemiological analysis of bovine ephemeral fever in 2012-2013 in the subtropical islands of Japan.

BACKGROUND: Bovine ephemeral fever (BEF) is a febrile disease of cattle that is transmitted by arthropod vectors such as mosquitoes and Culicoides biting midges. An outbreak of BEF recently occurred in Ishigaki Island and surrounding islands that are located southwest of Japan. In this study, an epidemiological analysis was conducted to understand the temporal and spatial characteristics of the outbreak. Factors associated with the disease spread within Ishigaki Island were investigated by hierarchical Bayesian models. The possibility of between-island transmission by windborne vectors and transmission by long-distance migration of infected vectors were examined using atmospheric dispersion models. RESULTS: In September 2012, the first case of the disease was detected in the western part of Ishigaki Island. In 1 month, it had rapidly spread to the southern part of the island and to surrounding islands, and led to 225 suspected cases of BEF during the outbreak. The dispersion model demonstrated the high possibility of between-island transmission by wind. Spatial analysis showed that paddy fields, farmlands, and slope gradients had a significant impact on the 1-km cell-level incidence risk. These factors may have influenced the habitats and movements of the vectors with regard to the spread of BEF. A plausible incursion event of infected vectors from Southeast Asia to Ishigaki Island was estimated to have occurred at the end of August. CONCLUSION: This study revealed that the condition of a terrain and land use significantly influenced disease transmission. These factors are important in assessing favorable environments for related vectors. The results of the dispersion model indicated the likely transmission of the infected vectors by wind on the local scale and on the long-distance scale. These findings would be helpful for developing a surveillance program and developing preventive measures against BEF.

Occurrence of bovine ephemeral fever in Okinawa Prefecture, Japan, in 2012 and development of a reverse-transcription polymerase chain reaction assay to detect bovine ephemeral fever virus gene.

In September 2012, several cows and a calf showed decreased activity, anorexia and fever on Ishigaki Island, Okinawa Prefecture, Japan, and the cases were diagnosed as bovine ephemeral fever (BEF). We isolated BEF virus (BEFV) from one of the affected cows and then determined the complete genome sequence of the G gene, which encodes a class I transmembrane glycoprotein of BEFV. The BEFV isolate in this case, ON-3/E/12, was sorted into the same cluster as other BEFV isolates in Japan, Taiwan and China obtained in 1996-2004 and was most closely related to a 2002 Chinese isolate, JT02L, according to the phylogenetic analysis of the complete G gene. Since inactivated vaccines for BEF available in Japan are considered effective against the ON-3/E/12 isolate as well as other isolates in East Asia from 1996-2004, annual vaccination should be conducted to prevent BEF in Okinawa. Additionally, in this study, we developed an RT-PCR assay to detect the BEFV gene in Japan and neighboring countries. Our assay was able to amplify target sequences in all of the tested BEFV isolates, including 18 isolates in Japan and another isolate in Australia. The assay was found to be useful also for testing RNA samples extracted from bovine peripheral blood mononuclear cells, and the detection limit of the assay was 10 copies per tube. We believe that our assay would be an important tool for the screening of BEFV infection and the diagnosis of BEF.