Isolation,Identification And Pathogenicity Analysis Of Gene VIK Subtype PPMV-1

Newcastle disease(ND)is a viral infection that can cause serious deaths in pigeons in recent years.It is one of the most important infectious diseases that harms the pigeon industry.Its pathogen is Pigen(Paramyxovirus type I,PPMV-1),belonging to the gene type VI Newcastle disease virus,also known as the pigeon Newcastle disease virus.The evolution rate of PPMV-1 is relatively fast.At present,the spread of the strain does not continue to expand,but maintains the constant evolution within a certain population.Therefore,it is necessary to monitor the spread of Newcastle disease virus in the pigeon farms in Guangdong Province and understand the current spread of PPMV-1 and the virulence.Moreover,the current Newcastle disease vaccines on the market are all genes of type I,II,III and VII,and there is no exclusive vaccine for gene VI.Therefore,the effect of these vaccines on the epidemic pigeon PPMV-1 remains to be studied.The research team conducted epidemiological surveillance of Guangdong provincial pigeon farms from December 2016 to June 2017.During the period,the blood samples were collected from 350 pigeon farms using the hemagglutination inhibition test(HI),and most of Guangdong Province was found.The number of Newcastle disease antibodies in the pigeons of the pigeon farm is lower.Significantly,since the pigeon farm is mainly used for the La Sota vaccine or the gene type VII vaccine,and there is no specific vaccine for the NDV gene type VI,when the HI test is performed,it is found that when the virus of different genotypes is used as the antigen,The measured antibody levels are very different.When the gene type VI strain is used as the antigen,the measured antibody level is low,which proves once again that the vaccine used by the pigeon farm will protect the pigeons of the infected gene type VI strain.Low.During the epidemiological investigation,a group of pigeons Newcastle disease(PPMV-1)virulent strain was isolated from the dead pigeons sent to a pigeon farm in Zengcheng,named PPMV-1/Guangdong/B5/2017,and then 3 Sub-plaque purification,whole-genome sequencing of the purified strain.Genetic phylogenetic tree analysis of the F gene indicated that the strain belonged to the gene type VI of class II of NDV.In order to understand the biological characteristics of the B5 strain,the pigeon pathogenicity test was carried out on the strain B5,and it was used to infect three groups of pigeons of different ages,namely 3 weeks old,6 weeks old and 12 weeks old.The infectious dose was 106 EID50.On the 3rd day and the 7th day of infection,3 mice were killed in each group to detect the replication of the virus in the pigeons.On the 3rd day of infection,the kidney,spleen and lung had the highest toxicity.On the 7th day of infection,the toxic content of brain,kidney,spleen and glandular stomach increased,indicating that the virus has broken through the blood-brain barrier.Obviously,the infected pigeons have obvious leg weakness,and they can't afford to tremble with the feet and tremble and turn their heads.The first-incidence mortality rate was 100%in the 3-week-old pigeon infection group and 100%in the cohabitation control group;the mortality rate in the 6-week-old pigeon infection group was100%,and the cohabitation control group mortality rate was 66%;the 12-week-old pigeon was slower.Clinical symptoms and death occurred,the mortality rate of the infected group was 83.3%,and the mortality of the cohabitation control group was 0%.The results showed that the B5 strain was a virulent strain that caused high morbidity and high mortality of pigeons.In order to test the protection of the current Newcastle disease vaccine against B5,three vaccines were designed to protect the PPMV-1 pigeons.Three-week-old pigeons were used to immunize La Sota attenuated vaccine,La Sota inactivated vaccine and gene type VII inactivated vaccine,and blood was collected on the 21st day after immunization to measure the antibody level of PPMV-1 in all pigeons.The HI results showed that the antibody levels of all immunized pigeons were positive,but the average antibody level was not high.On the22nd day of immunization,the infection test group had an infection rate of 10⁶ EID₅₀.The control group died all 12 days after infection,the mortality rate of NDV gene type VII vaccine immunization group reached 60%,and the mortality of La Sota attenuated vaccine group reached 30%.The protection ratio of La Sota inactivated vaccine was better,but it was not fully achieved.Protection,the mortality rate is 10%.During the infection,the diseased pigeons showed the symptoms of falling down,wings drooping,tremors of the feet,and weakness of the legs,which was consistent with the pathogenicity test of PPMV-1 on the pigeons.The results showed that the three vaccines could not fully protect B5.In order to evaluate whether the immunogenicity and biological characteristics of PPMV-1 are mutated or related to each other,the antigenic variation coefficient of PPMV-1 was analyzed easily,and the antigenic typing and antigenic differences among different strains were compared.In order to evaluate whether the immunogenicity and biological characteristics of PPMV-1 are mutated or related to each other,the antigenic coefficient of variation of PPMV-1 was analyzed easily,and the antigenic typing and antigenic differences among different strains were compared.The basis for the evaluation of sex size was called R value,the R value between PPMV-1 and La Sota was 0.597,and the R value between PPMV-1 and m GM was0.672.The results showed that PPMV-1 and La Sota and m GM were different subtypes.In summary,the isolation of B5 strains in a pigeon farm in Guangdong Province can lead to the death of different age pigeons.It is a virulent strain.Although the degree of disease can be reduced with age,12-week old birds can also produce a large number of deaths.And most of the pigeons raised in the pigeon farm are about 3 weeks old and less than 6 weeks old,so it can be concluded that the Guangdong provincial pigeon farm has already faced the threat of the virulent strain PPMV-1.However,at present,Newcastle disease vaccine can not produce better protection for pigeons.The protective effects of the three vaccines can not reach 100%.Among them,NDV gene type VII seedlings have the worst protection effect,followed by La Sota attenuated vaccine,La Sota inactivated seedling protection.The effect is better than the other two groups.Therefore,the development of vaccine against the Newcastle disease gene type VI is indispensable.Only the release of the gene VI vaccine as soon as possible can reduce the public health safety of PPMV-1 and the huge threat to the pigeon farm.