An outbreak of rabbit hemorrhagic disease (RHD) caused by Lagovirus europaeus GI.2/rabbit hemorrhagic disease virus 2 (RHDV2) in Ehime, Japan

Abstract

A total of ten 1-2-year-old rabbits died within 2 weeks at a facility in Ehime prefecture in May 2019. Necropsy revealed liver discoloration and fragility, hemorrhage of some organs and blood coagulation failure. On histopathologic examination, necrotizing hepatitis was a common finding, together with fibrin thrombi in the small vessels and hemorrhage in some organs. Rabbit hemorrhagic disease (RHD) virus gene was detected in liver samples, and viral particles of approximately 32 nm in diameter were found in the cytoplasm of degenerated hepatocytes by electron microscopy. Phylogenetic analysis based on the partial VP60 gene sequence classified it as Lagovirus europaeus GI.2/RHDV2. This is the first confirmed outbreak of RHD caused by globally emerging GI.2/RHDV2 in Japan.

Keywords: Japan; Lagovirus europaeus GI.2/RHDV2; electron microscopy; rabbit hemorrhagic disease (RHD).

Fig. 1.

Macroscopic findings of the necropsied rabbits. Discoloration of the liver (left) and hemorrhage of the lung (right).

Fig. 2.

Peripheral to midzonal necrosis in the liver with infiltration of a small number of inflammatory cells. CV: central vein. Hematoxylin and eosin. Bar=50 µm.

Fig. 3.

Viral particles in the degenerated hepatocyte (arrowhead). The viral particle measured approximately 32 nm in diameter. Membrane-like structure is shown by arrows. Transmission electron microscopy, double-stained with uranyl acetate and lead citrate. Bar=100 nm.

Fig. 4.

Phylogenetic tree based on the partial VP60 gene sequence of rabbit hemorrhagic disease virus (RHDV) using the Maximum Likelihood method based on the Tamura-Nei model with 1,000 bootstrap replications in MEGA 7 software. Bootstrap values above 60% are shown at the branch node. The sequences determined in samples from the current case (RHDV/Ehime-1/2019 and RHDV/Ehime-2/2019) and past cases in Japan (Tokyo-1/2000, Tokyo-2/2000, Hokkaido-3/2002, and Hokkaido-4/2002) are highlighted in red and blue, respectively.