Rabbit Haemorrhagic Disease (RHD) is extremely acute highly fatal, contagious disease with mortality rates of 80-90% of the infected rabbits. RHD causes hepatic, intestinal and lymphoid necrosis with massive terminal intravascular coagulopathy. The etiological agent is a member of caliciviridae lagovirus, Rabbit Haemorrhagic Disease Virus (RHDV); it is a single stranded RNA, non-enveloped and replicates in the cytoplasm. In pathogenesis studies, the primary sites of replication were in the small intestinal crypt and villous epithelium, hepatocytes and splenic lymphocytes. Apoptosis (programmed cell death) has been reported as being a constant feature of the pathogenesis of RHD. This work was planned to study the lesions associated with RHDV in small intestine at different intervals. Eighteen growing New Zealand rabbits (Oryctolagus cuniculus) aged 2-3 months allotted into two equal groups: control group (non infected) and infected group in which rabbits were experimentally inoculated with rabbit hemorrhagic disease virus (RHDV) through the nostril. All animals were dissected at 24, 48 and 72 hrs post infection. Histopathological, histochemical, immunohistochemical and biochemical studies were done for small intestine.
Macroscopic lesions in infected grower rabbits were consistent with RHD infection including congestion and haemorrhages of lung, liver necrosis and splenomegaly. Moreover, congestion of small intestine with multiple focal necrotic spots appeared from serosa and mucosa of intestine. Histopathological findings of the small intestine 24 hrs post infection (pi) showing necrosis of the crypts and villi atrophy, at 48 hrs pi shortening of villi and severe lymphocytic infiltration of the lamina propria were seen. 72 hrs pi showing severe atrophy and destruction of both villi and crypts. Immunohistochemical labeling for RHDV antigen on small intestine at different intervals 24, 48 and 72 hrs pi showed that epithelial cells and areas of focal necrosis exhibit strong immunolabeling in the intestinal villi where reactivity increases progressively. Serum biochemistry revealed highly significant increase in AST, ALT, urea and creatinine. To the best of our knowledge, it is the first report of the macroscopic lesions of small intestine in RHDV infected rabbits.