Rabbit hemorrhagic disease (RHD) is a highly contagious and fetal infectious disease caused by RHD virus. Japan experienced RHD outbreaks in 2019-2020 after an absence of the disease for 17 years. National Agriculture and Food Research Organization (NARO) conducted a whole-genome sequencing of RHD viruses that caused outbreaks between 2000 and 2020 and evaluated their genetic background. The evaluation showed that the RHD outbreaks in Japan may be caused by multiple incursions of foreign epidemic strains. Furthermore, it was revealed that the viral genome sequences from three cases that occurred in the Kanto region between 2019 and 2020 had high homologies to each other. RHD has been sporadically occurring in Japan even since 2021. Careful implementation of biosecurity, sanitation, and hygiene protocols should be taken at each farm or facility to prevent the virus incursion.
Overview
RHD, caused by RHD virus, is a highly acute infectious disease with a high mortality that mainly affects rabbits aged 8 weeks or older. However, a new variant that affect young rabbits as well as hares aged less than 8 weeks appeared in France in 2010. This variant virus is spreading rapidly all over the world. Hence there are new concerns about the losses on rabbit industry as well as its impact on the ecosystems due to the decline in the hare population.
In Japan, suspected case of RHD was first reported in 1994. After RHD was designated as a notifiable infectious disease under the Act on the Prevention of Infectious Diseases in Livestock in 1998, one case was reported in 2000 and one in 2002. Since then, there were no further outbreak for 17 years. However, a total of 9 cases of RHD occurred between 2019 and 2020, being the first epidemic of this disease in Japan.
Here, NARO conducted whole-genome sequencing and genetic analysis of RHD viruses detected in the samples from six outbreaks in Tokyo in 2000, Hokkaido in 2002, Ehime in 2019, Ibaraki in 2019, Tochigi in 2020, and Chiba in 2020 to understand the background of the epidemic and for future countermeasures. The results showed that RHD viruses detected in six outbreaks were classified into two groups with at least four origins; two of which belong to classical RHD virus and the other two to new variant. In addition, it was shown that the nucleotide sequences of RHD viruses were genetically rather related to the epidemic strains of other countries than the past domestic strains, except for three strains detected in outbreaks in Ibaraki Prefecture in 2019, Tochigi Prefecture in 2020, and Chiba Prefecture in 2020, that were highly similar to each other.
These results suggest that the RHD in Japan from 2000 to 2020 may have been caused by multiple incursions of foreign epidemic strains.
This disease has occurred sporadically in Japan even since 2021. It is necessary to carefully implement biosecurity, sanitation, and hygiene protocols on a daily basis in the facilities where rabbits are raised, to prevent the virus incursion through people, objects, introduced rabbits, etc. NARO will continue to collect information and develop testing and diagnostic methods. By this, we will actively strengthen the disease monitoring system and develop preventive methods.
Publication
Tanikawa T, Watanabe S, Mikami O, Miyazaki A. Genetics of the rabbit haemorrhagic disease virus strains responsible for rabbit haemorrhagic disease outbreaks in Japan between 2000 and 2020. J Gen Virol. 2023 May;104(5). doi: 10.1099/jgv.0.001846.
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