On the origins and relationships of Newcastle disease virus vaccine strains Hertfordshire andMukteswar, and virulent strain Herts'33

Abstract

The origins and relationships of Newcastle disease virus (NDV) vaccine strains Hertfordshire OI) andMukteswar, and the virulent Herts'33 were studied using partial sequence analysis of the fusion protein gene.The mesogenic strain H was obtained by egg passages of a field virus isolated in England in 1933 (later knownas Herts'33). Different lines of the strain Herts'33, however, divided into two distinct groups: genotype IV, and ahitherto undescribed lineage, which comprised the Weybridge line (Herts'33/56). Vaccine strain H and the twoclusters comprising viruses designated Herts'33 displayed 6.5 to 6.8% and 15.6 to 16.3% mutational distances,respectively, which precluded parent-offspring relationships with either of them. In contrast, the different linesof the vaccine strain Mukteswar, which was reportedly derived from an Indian field isolate in the mid-1940s,showed 98.9 to 100% sequence similarity to strain H. It is therefore probable that the two vaccines were derivedfrom the same virus stock.