| Mycoplasma synoviae(MS)is a common respiratory pathogen in chickens,which has a high infection rate in chickens.MS is conditional pathogenic bacteria that often requires the cooperation of other factors to exert its pathogenicity.Sometimes even minor respiratory injury caused by attenuated vaccine creates an opportunity for MS infection.When MS is mixed with other pathogens and under the environmental stress factors,it will cause respiratory symptoms,infectious synovitis,decline of egg production and quality,which cause great economic losses to chicken industry.This study verified the synergistic pathogenicity of MS with Infectious bronchitis virus(IBV),H9 subtype Avian influenza virus(AIV)and the attenuated live vaccine of Newcastle disease(ND).1.Study on the synergistic pathogenicity of MS and IBVA total of 60 one-day-old SPF chickens were kept in individual negative-pressure isolators and randomly divided into four groups:MS group,IBV group,MS+IBV group and negative control group.The experiment was carried out in negative pressure isolator.At 14 days of age,MS Ningxia/2017-1 strain was inoculated to MS group and MS+IBV group via the oculo-nasal rout,and the infection dose was 2.0×108CCU/chicken.At 3 days interval,chickens in IBV group and MS+IBV group were inoculated with CK/CH/JS/2010/12 strains of IBV via the oculo-nasal rout,and the infection dose was 105.5EID50/chicken.For 14 days from MS challenge,the morbidity and mortality of the chickens were observed and recorded every day.Serum and cleft palate swabs were collected at 3,7,10,and 14 days after MS inoculation.Antibody titers for MS and IBV in serum and MS load in cleft palate swabs were determined.The clinical results showed that no clinical symptoms were observed in the control group and MS group.3/15 of the chickens in the IBV group showed respiratory symptoms and 1/15 died.7/15 chickens in the MS+IBV group developed severe respiratory symptoms and 3/15 died.Compared with control group,MS group and IBV group,weight gain in MS+IBV group was significantly slower.The necropsy results showed that the MS+IBV group had air-sac lesion and tracheal hemorrhage,and 7/15 of the chickens had peritonitis,while the MS group showed only slight air-sac lesion.At the 3,7,10 and 14 day of MS challenge,the positive rate of MS antibody in MS+IBV group was significantly higher than that in MS group,and the positive rate of antibody in serum of the IBV group was 0/15,6/15,11/15 and 14/14,respectively;and the positive rate of antibody in serum of the MS+IBV group was 0/15,15/15,14/14 and 12/12,respectively.On the 7 and 10 day of MS challenge,the shedding of MS in the respiratory tract of MS+IBV group was significantly higher than that of MS group.On the 14 day of MS challenge,the shedding of MS in the respiratory tract of MS group could not be detected,while the shedding of MS in the respiratory tract of MS+IBV group remained at a high level.The above experimental results showed that the clinical morbidity and mortality of IBV CK/CH/JS/2010/12 strain were significantly increased under the condition of MS Ningxia/2017-1 strain infection.At the same time,IBV CK/CH/JS/2010/12 strain could also increase the shedding in the respiratory of MS Ningxia/2017-1 strain and enhance the pathogenicity.2.Study on the synergistic pathogenicity of MS and H9 AIV80 one-day-old SPF chickens were randomly divided into four groups:MS group,H9 AIV group,MS+H9 AIV group and negative control group.The test was carried out on a negative pressure isolator.At 14 days of age,MS group and MS+H9 AIV group were inoculated with MS Ningxia/2017-1 strain via the oculo-nasal rout at a infection dose of 2.0×108.0CCU/chicken;with an interval of 3 days,H9 AIV and MS+H9 AIV group administered H9 subtype AIV A/Chicken/Shandong/QD4/2013 strains,and the infection dose was 108.3 EID50/Chicken.After 28 days of MS challenge,the morbidity and mortality of the chickens were observed and recorded every day.Serum and cleft palate swabs were collected at 3,7,10,14,21 and 28 days after MS challenge to determine the antibody titer of MS and H9 AIV in serum and the load of MS and H9 AIV in cleft palate swabs.Clinical results showed that only 5/20 chickens in the MS+H9 AIV group developed respiratory symptoms,while the other groups had no symptoms.The MS+H9 AIV group showed airsacculitis and sternal cyst at autopsy,while the MS group had only slight air-sac lesions.No lesions were found in the control group or the H9 AIV group.Compared with the control group,weight gain was significantly slower in MS+H9 AIV group.At the same time,MS+H9 AIV group could induce a higher level of MS antibody titer.The shedding of MS in respiratory tract of MS+H9 AIV group was significantly higher than that of MS group,and the shedding of H9 AIV in respiratory tract of MS+H9 AIV group was significantly higher than that of H9 AIV group.The results showed that when MS and H9 subtype AIV were co-infected,the clinical morbidity was increased and even death cases occurred.3.Study on the synergistic pathogenicity of MS and ND attenuated vaccine80 one-day-old SPF chickens were randomly divided into four groups:MS group,ND attenuated vaccine group,MS+ND attenuated vaccine group and negative control group.The test was carried out on a negative pressure isolator.At 14 days of age,MS group and the MS+ND attenuated vaccine group were inoculated with the MS Ningxia/2017-1 strain(2.0×108.0CCU/chicken)by intranasal and intraocular routes.At 17 days of age,the ND attenuated vaccine and the MS+ND attenuated vaccine were vaccinated with ND attenuated vaccine(LaSota strain)at infection dose of 106.5 EID50/chicken.After 28 days of MS challenge,the morbidity and mortality of the chickens were observed and recorded every day.On days 3,7,10,14,21 and 28 after MS inoculation,serum and cleft palate swabs were collected to determine the antibody titer of MS and NDV in serum and the load of MS and NDV in cleft palate swab.Clinical results showed that after MS,the MS+ND attenuated vaccine group showed respiratory symptoms(5/20)and conjunctival congestion(1/20),while the other groups showed no symptoms.Only in the MS+ND attenuated vaccine group,air-sac lesions,kidney and spleen enlargement were found at autopsy,while no necropsy lesions were found in the other groups.Compared with MS group,MS+NDV attenuated vaccine group could induce a higher level of MS antibody titer.At the 21 day of MS challenge,the serum ND antibody titer of the attenuated NDV vaccine group was higher than that of the MS+attenuated ND vaccine group.During the trial,the shedding of MS in respiratory tract of MS+ND attenuated vaccine group was significantly higher than that of MS group,and the shedding of NDV in respiratory tract of MS+ND attenuated vaccine group was significantly higher than that of ND attenuated vaccine group.The results showed that ND attenuated vaccine could also enhance the pathogenicity of MS.In conclusion,this research through experimental proof in the case of infection with MS,then mix with the infection of IBV,H9 subtype AIV respiratory pathogens,such as ND attenuated vaccine,even may cause serious clinical symptoms and pathological changes,affect the growth and development of chicken,and cause serious economic losses,the importance and necessity of further evidence for MS purification. |
