aPMV-1 genome size is approximately 15 kb and encodes six genes, which produce nucleocapsid protein (NP), phosphoprotein (P), matrix protein (M), fusion protein (F), hemagglutininneuraminidase (HN), and polymerase protein (L) [10, 11] . RNAediting of P gene creates two additional proteins, V and W [12] . There are nine serotypes of aPMV-1; viruses associated with ND are in serogroup 1. Within serogroup 1 there are 2 major subdivisions, class I and II, based on phylogenetic grouping of the F gene [13] . Class I aPMV-1 are primarily recovered from waterfowl or samples from U.S. live bird markets, while the isolates from class II are commonly derived from poultry and other avian species [5, 14] . Eight genotypes of class II aPMV-1 can be identified [13] . Viruses belonging to genotypes I-IV have circulated since the 1930's. Genotype I and II consist of both lentogenic and velogenic viruses and have been associated with ND outbreaks in Australia and North America, respectively [5, 15, 16] . These viruses have been attenuated in culture and are used as modified live vaccines [16] . Genotypes V-VIII were first recognized in the mid-1960s [13] and contained only virulent viruses [16] . Genotype V was responsible for the second panzootic of ND in Europe from 1970-1974 and has been detected sporadically thereafter [17] . Genotype VI was described mainly from the Middle East and Asia during the 1980's-1990's [18] and genotype VII and VIII were reported in the 1990's from several countries [19, 20, 21, 22, 23, 24] . All genotypes, except IV [16] , are still in circulation.