| Atypical porcine pestivirus(APPV) is a causative agent of congenital tremor in newborn piglets.It is a new type of pestivirus,first reported in 2015.The virus can cause rhythmic tremors,jitter,and difficulty in breastfeeding in newborn piglets,often resulting in the death of sick piglets.With the first discovery of APPV,most countries in the world and parts of China have reported the outbreak and popularity of APPV,Which has caused widespread concern.Due to the wide variety of viral genotypes,there is still a lack of rapid and effective diagnostic methods and prevention measures,which poses a huge threat to the breeding industry.So,pathogen detection and genetic variation analysis of the virus,mastering its epidemic law and pathogenic characteristics are of far-reaching significance for the diagnosis,prevention and control of future diseases.In this study,RT-PCR was used to investigate the epidemiology of APPV.During the period of 2016-2018,in different regions of China(Guangdong,Guangxi,Fujian,Hainan,Heilongjiang,Hubei,Jiangxi,Sichuan,Yunnan,Zhejiang),a total of 1367 samples of different stages and types of disease were collected from 127 pig farms which were suspected APPV.The test results showed that the positive rate of APPV infection in the farm was 7.09%(9/127),and the positive incidence of APPV infection in all samples was 10.90%(149/1367).Among them,the positive rate of Guangdong pig farm was 12.50%(6/48),the proportion of positive samples was 43.62%(65/149);the positive incidence of Guangxi pig farm was 9.38%(3/32),and the proportion of positive samples was 56.38%.(84/149),a small number of pig farms in other provinces have not detected APPV.The positive detectable rate of pig feces and oral and nasal secretions was 4.12%(30/729),the seroprevalence rate was 7.14%(15/210),and positive rate of the tissue and organ was 24.30%(104/428).The results of fecal and oral secretions from pigs from three APPV-positive farms showed that the positive incidence of suckling pigs(1-20 days old)was 13.21%(14/106),The positive rate of nursery pigs(February-June)was 8.33%(10/120),the positive incidence of growth and fattening pigs was 2.48%(3/121),and the positive rate of lactating sows was 2.50%(3/120).In this study,a total of 9 E2 gene sequences were screened and obtained.The homology analysis showed the following results: The homology analysis showed that the nucleotide sequence homology of APPV E2 gene known in domestic and foreign was between 81.6% and 100%,but There is a large difference in homology with the CSFV E2 gene.According to the genetic evolution tree analysis: APPV Chinese strains discovered and identified in recent years belong to the same branch and belong to a closer relationship.The genome sequences of APPV/CNGL/2017(11445 bp)and APPV/CNYJ/2018(11468 bp)were successfully amplified,and the homology of other known APPV genes was between 83.3% and 98.3%,phylogenetic tree The analysis showed that the strains isolated from China were closely related,and they were far away from other countries’ foreign strains.They could form two small branches independently and proved to be new members of APPV.In this study,APPV pathogenicity experiments were performed on different animals.The virus was detected by RT-PCR in the brain,liver,spleen,lung and kidney tissues of KMinfected mice.Granulocyte-like degeneration was observed in liver tissue,and lymphoid necrosis of lymphocytes in spleen nodules was observed in spleen tissue.Focal hemorrhage could be seen in the tumor,and a small amount of microscopic pathological changes such as tubular tubule casts could be seen in the renal tissue.The virus was detected by RT-PCR in serum,liver and lung tissues of adult rabbits infected with APPV.In adult rabbits,the lung tissue was substantially mutated,accompanied by congestion and congestion,and inflammatory cells were found in liver,lung and kidney tissues.The virus was detected by RT-PCR in the serum,brain,heart,liver,spleen,lung,kidney and inguinal lymph nodes of the weaned piglets.The weaned piglets showed an increase in body temperature after infection,and the pancreas was found at the edge of the lung tissue accompanied by slight edema.large areas of liquefaction necrosis at the visible edge of the brain tissue,The number of neurons was greatly reduced.macroscopic pathological changes such as inflammatory cell infiltration in the heart,liver,lung,kidney and inguinal lymph nodes.q PCR was used to detect the average level of drug loading in 28 dpi of weaned piglets.The average copy number of each tissue in infected pigs was between 59-113 copies/μL,and the average drug load of lung tissue was the highest. |
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