| Infectious bronchitis(IB)is an acute and highly contagious disease caused by infectious bronchitis virus(IBV).There are many serotypes of IBV,and the cross-immune protection effect between different serotype strains is poor.Since the QX-type IBV was discovered in Shandong Province in 1997,which has been widely epidemic in China.At present,the QX-type has become the main serotype in China.Due to the fact that Mass-type strains have a distant relationship with the current popular QX-type strains,Mass-type vaccines are less effective in preventing and controlling QX-type IBV,which have been widely used in China for many years.Therefore,the development of QX attenuated vaccine is of great significance for the prevention and control of IB in China.Bi-combined Attenuated Vaccine of Newcastle Disease and Infectious Bronchitis(La Sota Strain + QXL87 Strain)developed by our laboratory will soon acquire a new veterinary drug certificate.To better promote the vaccine,this study evaluated the protective efficacy of the vaccine against the epidemic strains of IBV.1 Protective efficacy of bi-combined attenuated vaccine(La Sota strain + QXL87 strain)against QX strainsThe QX-type IBV has been subdivided into subtype Ⅰ and Ⅱ,and the subtype Ⅰ was reported early,while the subtype Ⅱ had been detected since 2010.In this study we evaluated the protective efficacy of the bi-combined attenuated vaccine(La Sota strain + QXL87 strain)against different subtypes of QX strains.The CK/CH/JS/2006/2 strain(JS-2 strain)used in this study belongs to subtype Ⅰ,while the stains of CK/CH/JS/2016/1(JS-1 strain)and CK/CH/FJ/2016/1(FJ-1 strain)belong to subtype Ⅱ.1-day-old SPF chickens were divided into 6 groups(n=10).Three groups were immunization groups and the chickens were inoculated nasally and ocularly with the bi-combined attenuated vaccine(La Sota strain + QXL87 strain),and the dose of immunization was 103.5 EID50/0.1mL。The other three groups were control groups.14 days after immunization,the immunization and control groups were challenged with JS-1 strain,FJ-1 strain and JS-2 strain,respectively,through the way of intranasal and intraocular dropping at the dose of 104.0 EID50/0.1mL.We counted the incidence and death of each experimental group daily after challenge.The virus content in throat swabs and cloacal swabs(collected on days 5,7 and 9)were detected after challenge by using the real-time fluorescence quantitative PCR.14 days after challenge,all chickens were autopsied to examine lesions of the trachea and kidney.The tracheal ring was prepared by collecting trachea,and the movement of cilia in tracheal epithelial cells was observed under a microscope.The bi-combined attenuated vaccine(La Sota strain + QXL87 strain)could provide more than 80%protection against subtype Ⅰ and Ⅱ QX strains.The result showed that the immunization group had significantly lower virus shedding after challenge than the control group.After necropsy,there was a lot of mucus in the larynx,with cilium stagnation and kidney enlargement in control groups.However,no significant lesions were found in the immunized group.2 The comparison of protective efficacy between bi-combined attenuated vaccine(La Sota strain+ QXL87 strain)and other IB live vaccines against QX strainsAlthough the QX type has become the most prevalent serotype in China,no vaccine against this serotype has been approved for listing.Currently IB live vaccines used in China include three serotypes,Mass-type(H120 strain and Ma5 strain),tl/CH LDT3/03-type(LDT3-A strain),793/B-type(4/91 strain),respectively.In this study,we compared the bi-combined attenuated vaccine(La Sota strain+ QXL87 strain)with four other IB live vaccines(H120 strain、Ma5 strain、LDT3-A strain and 4/91 strain)so as to evaluate the immunoprotection effect against QX strains.1-day-old SPF chickens were divided into 6 groups(n=10).Five groups were immunization groups and the chickens were inoculated nasally and ocularly with the bi-combined attenuated vaccine(La Sota strain + QXL87 strain)and four other IB live vaccines,and the dose of immunization was 103.5 EID50/0.1mL.The other was control group.14 days after immunization,the immunization and control groups were challenged with the CK/CH/JS/2010/12(QXL strain)through the way of intranasal and intraocular dropping at the dose of 104.0 EID50/0.1mL.We counted the incidence and death of each experimental group daily after challenge.The virus content in throat swabs and cloacal swabs(collected on days 5,7 and 9)were detected after challenge by using the real-time fluorescence quantitative PCR.14 days after challenge,all chickens were autopsied to examine lesions of the trachea and kidney.According to the evaluation of clinical symptoms,the protective rate of the bi-combined attenuated vaccine(La Sota strain +QXL87 strain)and Ma5 strain immunization groups reached 80%,while the protective efficacy of H120 strain and LDT3-A strain immunization groups were only 10%～30%.7 days after the challenge,the amount of virus shedding of the bi-combined attenuated vaccine(La Sota strain +QXL87 strain)immunization group reached the peak,which was significantly reduced compared to the other 4 immunization groups(P<0.05).Combined with clinical protection and virus shedding protection,the bi-combined attenuated vaccine(La Sota strain + QXL87 strain)had significantly better immune protection against QXL strain than the other four vaccines.3 Protective efficacy of bi-combined attenuated vaccine(La Sota strain+QXL87 strain)against TW-1 and TC07-2 strainsIn addition to the QX strains,there are also a certain proportion of other serotype virulent strains in China at the same time,the most common being TW-I type and TC07-2 type.In order to evaluate the efficacy of the vaccine on cross-immune protection against non-QX strains,the chickens were immunized with the bi-combined attenuated vaccine(La Sota strain + QXL87 strain)and challenged with TW-I and TC07-2 virulent strains in this study,respectively.1-day-old SPF chickens were divided into 4 groups(n=20).Two groups were immunization groups and the chickens were inoculated nasally and ocularly with the bi-combined attenuated vaccine(La Sota strain + QXL87 strain),and the dose of immunization was 103.5 EID50/0.1mL.The other were control groups.14 days after immunization,the immunization and control groups were challenged with the TW-I-type(AH/2011/3 strain)and TC07-2-type(FJ/2017/1 strain)through the way of intranasal and intraocular dropping at the dose of 104.0 EID50/0.1mL.We counted the incidence and death of each experimental group daily after challenge.The virus content in throat swabs and cloacal swabs(collected on days 5,7 and 9)were detected after challenge by using the real-time fluorescence quantitative PCR.14 days after challenge,all chickens were autopsied to examine lesions of the trachea and kidney.The results showed that the clinical protective efficacy of the bi-combined attenuated vaccine(La Sota strain + QXL87 strain)against the strains AH/2011/3 and FJ/2017/1 was 60%and 65%,respectively.However,there was no significant difference in virus shedding between the immunized group and the challenge contol group(P>0.5).To sum up,the bi-combined attenuated vaccine(La Sota strain + QXL87 strain)could only provide partial immune protection for TW-I and TC07-2 strains. |
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