Jackwood Mark W, Hilt Deborah A, McCall Amber W, Polizzi Crystal N, McKinley Enid T, Williams Susan M
Department of Population Health, Poultry Diagnostic and Research Center, 953 College Station Road, University of Georgia, Athens, GA 30602, USA.
Avian Dis. 2009 Jun;53(2):175-83. doi: 10.1637/8465-090308-Reg.1.
To determine the coverage of infectious bronchitis virus (IBV) vaccine field boost in commercial broilers, estimate the relative amount of vaccine virus in the trachea, and follow the clearance of the vaccine, we collected approximately 100 tracheal swabs at various times postvaccination from 10 different flocks and used real-time reverse transcriptase-PCR (RT-PCR) to detect the virus. This allowed us to detect vaccine virus in as few as 3% of the birds in a flock of 20,000 birds with a 95% confidence level. We found that the number of birds positive for IBV vaccine following vaccination in the field resembled a parabolic-shaped curve that peaked around 14 days postvaccination, or it resembled a sinusoidal-type wave with a frequency of about 2 wk. The patterns did not appear to correlate with water or spray vaccination methods, nor did they correlate with the type of backpack sprayer used. The highest number of positive birds in a flock ranged from 66% to 100%. The viral genome copies in the tracheal swabs, as determined by real-time RT-PCR, ranged from 1 x 10(2.6)/ml to 1 x 10(5.2)/ml and, in most studies, had a positive correlation with the number of birds positive for vaccine virus in the flock. On the last sample day of each study, 21, 28, or 35 days postvaccination, from 12% to 66% of the birds were still positive for vaccine virus, and although different IBV vaccine types were used in each study, only Arkansas vaccine virus was identified in selected samples on those days. Arkansas vaccine virus was also the only virus identified in selected samples at 1, 3, and 5 days postvaccination, clearly indicating that Arkansas vaccine virus is persisting in the birds. Protection studies conducted on birds vaccinated with Arkansas- and Delaware-type vaccines and removed from the field at 21 days postvaccination showed complete protection against challenge with Delaware (except for one bird), whereas protection against Arkansas challenge was between 37.5% and 62.5%. Our findings show that introduction of IBV vaccines into a commercial broiler flock do not necessarily follow a seemingly logical pattern of a high number of birds infected followed by clearance from the trachea, but resembled either a parabolic curve or a sinusoidal-type wave. In addition, Arkansas vaccine viruses are clearly persisting in commercial broilers, which may be because of incomplete protection observed for that IBV type.
为了确定传染性支气管炎病毒（IBV）疫苗在商品肉鸡中的田间加强免疫覆盖率，估计气管中疫苗病毒的相对含量，并追踪疫苗的清除情况，我们在接种疫苗后的不同时间从10个不同鸡群中收集了约100份气管拭子，并使用实时逆转录聚合酶链反应（RT-PCR）检测病毒。这使我们能够在置信水平为95%的情况下，在一个20000只鸡的鸡群中检测到低至3%的携带疫苗病毒的鸡。我们发现，田间接种IBV疫苗后呈阳性的鸡的数量类似于一条抛物线形曲线，在接种后约14天达到峰值，或者类似于一条频率约为2周的正弦波。这些模式似乎与饮水或喷雾接种方法无关，也与使用的背负式喷雾器类型无关。一个鸡群中阳性鸡的最高比例在66%至100%之间。通过实时RT-PCR测定，气管拭子中的病毒基因组拷贝数在1×10(2.6)/ml至1×10(5.2)/ml之间，并且在大多数研究中，与鸡群中疫苗病毒阳性鸡的数量呈正相关。在每项研究的最后一个采样日，即接种后21、28或35天，12%至66%的鸡仍对疫苗病毒呈阳性，尽管每项研究中使用了不同类型的IBV疫苗，但在那些日子的选定样本中仅鉴定出阿肯色州疫苗病毒。阿肯色州疫苗病毒也是在接种后1、3和5天的选定样本中鉴定出的唯一病毒，这清楚地表明阿肯色州疫苗病毒在鸡体内持续存在。对接种阿肯色州和特拉华州疫苗并在接种后21天从田间取出的鸡进行的保护研究表明，对特拉华州毒株的攻击具有完全保护作用（除一只鸡外），而对阿肯色州毒株攻击的保护率在37.5%至62.5%之间。我们的研究结果表明，将IBV疫苗引入商品肉鸡群后，不一定会遵循一种看似合理的模式，即大量鸡被感染后病毒从气管中清除，而是类似于一条抛物线或正弦波。此外，阿肯色州疫苗病毒在商品肉鸡中明显持续存在，这可能是因为对该IBV毒株观察到的保护不完全。
