Antigenic and molecular analyses reveal that the equine rotavirus strain H-1 is closely related to porcine, but not equine, rotaviruses: interspecies transmission from pigs to horses?

We have sequenced the genes encoding the inner capsid protein VP6 and the outer capsid glycoprotein VP7 of the subgroup (SG) I equine rotavirus strain H-1 (P9[7], G5). The VP6 and VP7 proteins of the equine rotavirus strain H-1 shared a high degree of sequence and deduced amino acid identity with SG I porcine strains and serotype G5 porcine strains, respectively. Previous sequence analyses of the genes encoding the outer capsid spike protein VP4 and the nonstructural proteins NSP1 and NSP4 of equine H-1 strain also revealed a high degree of sequence and deduced amino acid homology with the prototype porcine rotavirus strain OSU (P9[7], G5). We have also confirmed and extended the VP4 and VP7 antigenic relatedness of equine rotavirus strain H-1 to porcine strains of P9[7] and G5 serotype specificities isolated in the United States, Venezuela, Argentina, and Australia based on cross-neutralization studies. In addition, the pathogenicity of tissue culture-adapted equine H-1, H-2, FI-14, FI-23, and L338, and porcine OSU rotavirus strains was compared in the neonatal mouse model. The 50% diarrhea dose (DD50) of equine H-1 was similar to that of porcine OSU and equine H-2 and L338 strains, while the DD50 of equine H-2 was > or = 50 or 315-fold lower than those of equine FI-14 or FI-23, respectively. Our sequence comparison of NSP4 of the rotavirus strains tested potentially identified amino acid residue 136, within the variable region spanning amino acids 130 to 141, as playing a role in virulence. Taken together, there is strong support to suggest that the equine rotavirus strain H-1 may represent an example of interspecies transmission from pigs to horses.