Complex sentence: The virus is divided into four major serotypes (adr, adw, ayr, ayw) based on antigenic epitopes present on its envelope proteins, and into ten genotypes (A--J) and forty subgenotypes according to overall nucleotide sequence variation of the genome.
Split into simpler sentences: The virus is divided into four major serotypes (adr, adw, ayr, ayw) based on antigenic epitopes present on its envelope proteins. The viral strains have also been divided into ten genotypes (A--J) and forty subgenotypes according to overall nucleotide sequence variation of the genome.