Arch Virol (1992) 124:363-370 _Archives Vi rology © Springer-Verlag 1992 Printed in Austria European brown hare syndrome in the U.K.; a calicivirus related to but distinct from that of viral haemorrhagic disease in rabbits Brief Report D. Chasey,M. Lucas, D. Westcott, and M. Williams Central Veterinary Laboratory, Weybridge, Surrey, U.K. Accepted November 7, 1991 Summary. The virus recovered from cases of European brown hare syndrome in the U.K. contains one major capsid protein of approximately 60 k molecular weight and morphologically resembles known caliciviruses. It has been com- pared with a European isolate of rabbit haemorrhagic disease calicivirus and, although it shows some antigenic similarity, it is not identical. In transmission and protection studies the virus from U.K. hares failed to produce disease in rabbits and did not effectively protect against subsequent challenge with the rabbit calicivirus. European brown hare syndrome (EBHS) has been reported in several European countries including the United Kingdom and occurs in both wild and farmed hares (Lepus europaeus) [2, 4-8, 11, 14, 18]. Clinical signs are variable but affected animals often appear depressed, and can exhibit anorexia, muscular tremors, and incoordination. Death occurs within 3 days of the onset of clinical signs and mortality rates can reach 100%. At post-mortem gross lesions are not consistent but generalised congestion is a feature, with lung and tracheal involvement, and there is usually marked necrosis of the liver. The syndrome was originally considered to be linked to the grazing of oil- seed rape but no evidence for any toxic effect has been reported. Although the aetiology may be mixed a small unenveloped virus has now been identified and is found in many disease outbreaks. The virus can be detected, usually in the liver, by electron microscopy, and has been described as a picornavirus on the basis of its apparent morphology when examined directly in homogenised tissue using phosphotungstic acid (PTA), pH 6.6, as a negative stain I-4, 9].