| Newcastle disease,also known as Asian Fowl pest,is a common kind of poultry disease which can cause a variety of respiratory and neurological symptoms.This disease was recognized in 1926 for the first time,and has caused four world-wide pandemics,brought great damage to the world economy.According to the pathogenicity in chickens,NDV is generally categorised into three pathotypes:velogenic,mesogenic and lentogenic.It is divided into two categories,class Ⅰ and class Ⅱ,depended on the nucleotide sequence of fusion protein which is the main virulent protein.Class Ⅰ strains are usually lentogenic,they can be divided into at least 4 genotypes:1a,1b,1c,1d,isolated mainly from wild waterfowl and live bird markets.Class Ⅱ contains the majority of virulent strains with at least 18 genotypes(Ⅰ-ⅩⅧ).The epidemiological investigation of Newcastle disease virus is conducive to the study of its evolution and development,and is of great significance to the early warning,prevention and control of the disease.In this study,we collected 1973 samples and isolated 4 Newcastle disease virus strains in wild animal nature reserves and live bird markets in parts of Jiangsu province.The source of the isolated strains is an oropharyngeal swab of Eurasian Coot,an oropharyngeal swab of domestic chicken,an oropharyngeal swab and a cloacal swab of two mallard,respectively.The clinical characterization of these hosts was apparently healthy.The positive rate of Newcastle disease virus of the total samples was 0.203%,among which the positive rate of wild animals was 0.218%,which was higher than the rate of live bird markets(0.168%).The F gene of the four isolates was amplified and obtained the full length of it.All of the four ORF was 1662nt,encoding 553 amino acids.It was found that the amino acid sequence at the cleavage site of F protein showed typical sequence characteristics of lentogenic strain,so they were predicted to be lentogenic;moreover,it was found that partial amino acid mutations occured at the important sites and main functional areas of F protein of the four isolates,but they were basically consistent with other strains which belong to the same genotypes.The results of genetic evolution showed that the isolates belonged to genotype 1d of class Ⅰ,genotype Ⅱ of class Ⅱ,and genotype Ib of class Ⅱ,respectively.The genotype 1d of classⅠ strain has the closest homologous relationship with the US strain Mallard/USA/MN/AI12-3156/2010 which isolated in 2010,so it may be a foreign strain.The genotype Ⅱ of class Ⅱ isolate has the highest homology with the La Sota strain which is a vaccine strain,in this way,it may be the vaccine strain or evolved from it.The two genotype Ⅰb of class Ⅱ stains are similar with the Russian isolate Uria_aalge/Russia/Tyuleniy_Island/109/2015 and domestic isolate NDV/Anser fabalis/CN/HN/F2-119-2/2016,so it may be an infected strain of a foreign strain or other domestic strain.The complete genome of the class Ⅰ strain was amplified and sequenced,the full length of the genome was 15198nt,which follow the ’rule of six’ principle which required for the replication of Newcastle disease virus,the sequence of genome is in the order of 3’-NP-P-M-F-HN-L-5’,the characterization of genome were basically consistent with other class Ⅰ strains.The results of genetic evolution showed that it belongs to genotype 1d which has high homology with the North American isolate.This is the first genotype 1d of class Ⅰstrain which identified in China,indicating that new genotype of Newcastle disease virus has increased in China.This study provides new data support for the epidemiological study of Newcastle disease virus in Jiangsu Province,and is of great significance for the evolution analysis and disease prevention and control of Newcastle disease virus. |
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