B亚型禽偏肺病毒灭活疫苗对商品肉鸡免疫效果的研究

Study on immune effect of inactivated vaccine of avian metapneumovirus(subtype B)on commercial broiler chickens

为了研究B亚型禽偏肺病毒(a MPV/B)灭活疫苗对商品肉鸡的免疫保护效果,本研究选取21日龄的商品肉鸡,将前期研制的a MPV/B灭活疫苗通过肌肉注射的方式免疫商品肉鸡(0.5 mL/只),以注射相同剂量PBS的商品肉鸡作为阴性对照组。于首免后3周加强免疫1次,分别采用ELISA和中和试验检测首免1周~6周后各组鸡血清中的IgG抗体效价和中和抗体效价。结果显示,首免后3周及加强免疫后3周(首免后6周),各组鸡血清平均IgG抗体效价分别为1:11864和1:36619,平均中和抗体效价分别为4.7 log2和6.5 log2。而阴性对照组鸡血清均无IgG抗体和中和抗体产生。加强免疫后3周以a MPV/B LN16株(5000 TCID_(50)/只)攻毒,观察攻毒后1 d~7 d各组鸡的临床症状,统计免疫保护率。结果显示,免疫组有一只鸡挤压有鼻液,其他鸡均无明显症状,发病率为10.0%,而对照组鸡出现混浊或粘稠泡沫样、牵丝状鼻液,鼻痂等症状,且发病率达90.0%,经计算,疫苗免疫保护率达88.9%;通过RT-qPCR检测首免后1 d~6 d采集的各组鸡鼻腔拭子中的病毒基因拷贝数,分析其排毒情况。结果显示,攻毒后1 d~6 d,免疫组鸡鼻腔拭子中的病毒拷贝数较对照组鸡下降64.6%~80.7%;攻毒后9 d剖杀各组鸡,采集各组鸡鼻甲、气管及肺组织,制作病理切片后观察各组织病理学变化。结果显示,对照组鸡的鼻甲黏膜、气管黏膜及肺房壁均可见炎性细胞浸润,而免疫组鸡上述各组织均未见明显病理变化。本研究首次表明,aMPV/B灭活疫苗能够诱导商品肉鸡产生较高水平的体液免疫反应,并且对鸡产生较好的免疫保护效果。本研究对控制a MPV/B的传播与流行具有重要意义。

In order to study the immune protection effect of inactivated vaccine of subtype B avian metapneumovirus(aMPV/B)on commercial broilers,commercial broilers at 21 days of age were selected and immunized intramuscularly with the previously developed inactivated vaccine(0.5mL per chicken).Commercial broilers injected with the same dose of PBS were set as the control group.Three weeks after the priming immunization,the chickens were given a boosting immunization.ELISA and neutralization test were performed for the detection of serum IgG antibody titers and neutralization antibody titers from 1 to 6 weeks post primary immunization.The results showed that the mean ELISA antibody titers were 1:11864 and 1:36619 at 3 and 6 weeks after primary immunization,and the mean neutralization titers were 4.7 log2 and 6.5 log2,respectively.No neutralizing antibodies were detected in the negative control group.The chickens were challenged with a MPV/B LN16(5000TCID_(50)per chicken)3 weeks after the boost immunization.Clinical symptoms were monitored from 1 to 7 days after challenge,and the protection rate was analyzed.The results showed that one chicken in the immune group had nasal fluid extrusion,and the other chickens had no obvious symptom The incidence rate of the immune group was 10.0%.Chickens in the control group had cloudy or sticky foam-like nasal fluid,nasal callus and other symptoms,and the incidence rate was 90.0%.It was calculated that the immune protection rate was 88.9%.RT-qPCR was performed to detect the viral genomic copy numbers in nasal swabs collected from 1 to 6 days after the first immunization.The results showed that the viral copy number in nasal swabs of the vaccinated group decreased by 64.6%-80.7%compared with that of the challenged control group.At 9 days after challenge,the chickens in each group were dissected,and the turbinate trachea and lung tissues of the chickens were collected and made pathological sections for histopathological observation The results showed that inflammatory cell infiltration could be seen in the turbinate mucosa,tracheal mucosa and pulmonary chamber wall of the chickens in the control group,but no obvious pathological changes were found in the immunized group.This study has important significance for controlling the spread and epidemic of aMPV/B in China.The results of this study showed for the first time that aMPV/B inactivated vaccine could induce high humoral immune response in commercial broilers and had a good immune protective effect on chickens after challenge.This study is of great significance to control the spread and prevalence of aMPV/B.