A further step in the evolution of rabbit hemorrhagic disease virus: the appearance of the first consistent antigenic variant

Rabbit hemorrhagic disease virus (RHDV) is a noncultivable calicivirus that infects rabbits (Oryctolagus cuniculus) and causes epidemics of an acute f atal hepatitis. In 1997 we identified two RHDV isolates from geographically distant Italian regions, which differed antigenically from the reference s train RHDV.Bs89. In fact, they were not reactive with mAb 1H8, that is able to protect rabbits from RHD and showed a low reactivity with the rabbit co nvalescent serum raised against RHDV.Bs89. Experimental infection of rabbit s with either RHDV isolates confirmed their high pathogenicity and their pe culiar antigenic profile; nevertheless, rabbits vaccinated with the current vaccine were protected against challenge infection with these isolates. Se quence comparison definitely demonstrated that the two isolates originated from the same RHDV variant and that the similarity of their structural prot ein (VP60) sequences with the RHDV.Bs89 is equal to 93%. This variant was n amed RHDVa since shows consistent genetic and antigenic differences from th e wild-type RHDV. In particular, 44% of amino acid substitutions in RHDVa V P60 were located between amino acids 344 and 370, where the similarity with RHDV.Bs89 drops to 70%, suggesting that this region probably contains the epitope recognized by mAb 1H8. In addition: this paper presents preliminary data concerning the amino acids of VP60 involved in the hemagglutination s ite of the virus. (C) 1998 Elsevier Science B.V. All rights resented.