Recently, the Waterfowl viral infectious diseases innovation research group led by Prof. Chan Ding at the Shanghai Veterinary Research Institute (SHVRI) of Chinese Academy of Agricultural Sciences (CAAS) identified quasispecies diversity as a novel mechanism of Newcastle disease virus (NDV) virulence enhancement. This finding has been published in the Journal of virology on Dec 9 2015 available here: http://jvi.asm.org/content/early/2015/12/08/JVI.01801-15.full.pdf+html
 Phylogenetic analysis of NDV evolution showed that velogenic viruses likely emerged from a lentogenic progenitor virus via change two amino acids at the F0 cleavage site. The researchers passaged an avirulent isolate JS10 through chicken air sac and embryos, and the pathogenicity of the variants was assessed. A virulent variant, JS10-A10, was generated from consecutive passage in air sacs. And they developed a deep sequencing approach to detect of low-frequency viral variants across the NDV genome and observed that virulence enhancement of JS10 was due to the selective accumulation of velogenic quasispecies and the concomitant disappearance of lentogenic quasispecies. Their results suggest that because it is difficult to avoid contact between natural waterfowl reservoirs and sensitive poultry operations, circulating lentogenic NDV strains may represent a potential reservoir for emergent velogenic NDV strains that could cause outbreaks in chickens.