Vaccination against and immune response to viral haemorrhagic disease of rabbits: a review of research in the People's Republic of China.

Viral haemorrhagic disease (VHD) of rabbits is an acute entity with high mortality which affects adult rabbits. Several vaccines have been developed in China and extensive use of these vaccines in the field has controlled the spread of the disease. Formalin inactivated tissue vaccine induces solid immunity on the third to fourth day post vaccination and immunity lasts for at least six months. The oil-emulsion tissue vaccine which has been developed has longer lasting potency. Successful adaptation of VHD virus (VHDV) to cultured cells and preliminary immunisation will provide the possibility of large-scale production of cell-cultured virus vaccine. Passive, emergency immunisation with hyperimmune antiserum provides short-term protection of threatened rabbits as well as treatment of infected rabbits in the field. Histopathological and pathophysiological studies reveal that immune cells and organs are the most affected targets in infected rabbits; owing to the damage to the endothelial system of blood vessels, extensive disseminated intravascular coagulation (DIC) occurs in the parenchymal tissues. Destruction of the immune system and the occurrence of DIC lead to acute illness and sudden death post infection. Experimental immunological studies demonstrate that the induction of rapid immunity is coordinated by macrophages and T and B lymphocytes in the initial, post-immunisation stage, whereas humoral immunity plays the main role in long-term protection against VHDV infection. The positive association of post-vaccination protection with haemagglutination inhibition antibody can also be observed. Interferon probably takes effect as an anti-VHDV agent soon after vaccination.