Pigeon NDV or PPMV-1 is a highly pathogenic and severe infectious disease. Both young and adult pigeons can be infected, which caused significant economic losses in the pigeon industry (5, 15). Although some strains of PPMV-1 are non-pathogenic in chickens, they cause morbidity in pigeons. The disease signs in pigeons are consistent with that in chickens, and generally include a series of nervous disorders: bilateral or unilateral locomotor disturbances of wings or legs, torticollis, and watery green diarrhea. If pigeons were infected during breeding or molting, the mortality would tend to increase.
Most pigeon-derived virulent isolates belong to class II of NDV. NDV strains of several genotypes were isolated and detected in pigeons, including genotype VI, VII and XXI (13, 20, 21). In China, the strains that infect pigeons are mainly genotype VI (11, 13–15).. The two strains also belong to genotype VI, suggesting that genotype VI is the dominant strain in pigeon in China. The genotype VI strains can infect many kinds of birds, including pigeons, chickens, turkeys, quails, and geese (5). However, it would not cause obvious symptoms in other species (22). There are still potential hazards to the aquaculture industry. Therefore, it is very important to implement epidemiological testing for PPMV-1.
The classification of NDV genotypes were renewed by Dimitrov et al (3). Namely, former VIc, VIl, VIi, VIg and VIm sub-genotypes were confirmed and renamed as genotype XX and XXI (3). Thus, the homogeneity of the two strains were with a close genetic distance from these three genotypes (VI, XX and XXI). Moreover, genotype VI strains can be further divided into at least seven sub-genotypes (VI.1, VI.2.1.1, VI.220.127.116.11.1, VI.18.104.22.168.2, VI.2.1.2, VI.2.2.1, VI.2.2.2) (3). At present, the genotypes of PPMV-1 that are prevalent in other countries are VI.1, VI.2.1.1, VI.2.1.2, VI.2.2.1. The genotypes prevalent in China are mainly VI.2.2.2, VI.22.214.171.124.1, VI.126.96.36.199.2(3). Tian et al. found that ten PPMV-1 viruses isolated in China during 1996–2019 belonged to sub-genotypes VI.2.2.2, VI.188.8.131.52.1, VI.184.108.40.206.2 and genotype VII (13). Additionally, Zhan et al. reported that 21 PPMV-1 isolates belonged to sub-genotypes VI.220.127.116.11.1 and VI.18.104.22.168.2 in China from 2007 to 2019 (14). In this study, we identified two strains of PPMV-1 from Jiangsu province in China in 2006 and 2017, they were classified into sub-genotype VI.22.214.171.124.1 and VI.2.2.2. The above results indicated that the prevalence of PPMV-1 was the result of different genotype strains circulating in China. Besides, several novel mutations were also detected (I20, M22, V235, S515 mutation in F protein and I253, H280, I326, S365 mutation in HN protein). It indicated that the overall variation rate of the genotype VI strain amino acids was rather fast. It should be noticed that all the novel mutations were in the sub-genotype VI.2.2.2 strain, suggesting it might become a new sub-genotype.
In summary, the full genomes of two genotype VI viruses isolated from pigeons in Jiangsu Province were identified and analyzed based on a recently unified phylogenetic classification system. The sub-genotype VI.126.96.36.199.1 and VI.2.2.2 strains showed high virulence and shedding efficacy in pigeons. The results showed that the prevalence of genotype VI NDV was contributed by strains from diverse sub-genotypes. Although these isolates were only found in Jiangsu Province, it had undergone a certain degree of variation, suggesting the importance of NDV prevalence and evolution surveillance in China. It would further lay a foundation for the subsequent development of pigeon ND vaccine.