Matthijs M G R, Bouma A, Velkers F C, van Eck J H H, Stegeman J A
Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Marburglaan 2, 3584 CN Utrecht, The Netherlands.
Avian Dis. 2008 Sep;52(3):461-6. doi: 10.1637/8204-010708-Reg.1.
The aim of this study was to quantify transmission of infectious bronchitis virus (IBV) H120 vaccine strain among broilers, and to assess whether birds that have been exposed to vaccine strain-shedding birds were protected against clinical signs after infection with a virulent strain of the same serotype. A transmission experiment and a replicate were carried out, each with six groups of commercial broilers. At day of hatch (n = 30) or at 15 days of age (n = 20), half of each group was inoculated with either IBV H120 vaccine (H120 group), virulent IBV M41 (M41 group), or were mock-infected, thereby contact-exposing the other half of each group. Nasal discharge was recorded, and antibody response and virus shedding were measured. To measure clinical protection, four weeks after inoculation all birds, in all groups, were challenged with IBV M41. The reproduction ratio (R; the average number of contact infections caused by one infectious bird) was determined to quantify virus transmission. All contact-exposed birds, except for one in an H120 group, became infected with either IBV H120 or IBV M41. Almost all birds contact-infected with IBV H120 or IBV M41 were subsequently protected against clinical signs after challenge with IBV M41. The lower limits of the 95% confidence interval (CI) of the R of IBV H120 vaccine, and of IBV M41, were significantly <1. For both IBV H120 and IBV M41, the 95% CI was [2.1-infinity] following inoculation at day of hatch and [1.8-infinity] after inoculation at 15 days of age. This finding demonstrates that IBV H120 vaccine is able to spread extensively among broilers. This implies that this vaccine strain might be able to become endemically present in the poultry population. It also implies that, even if not all birds received vaccine during spray application, due to the ability of the vaccine to spread in the flock, they will most likely be protected against clinical signs after a subsequent field virus infection.
本研究的目的是量化传染性支气管炎病毒（IBV）H120疫苗株在肉鸡中的传播，并评估接触过排出疫苗株的禽类在感染相同血清型的强毒株后是否能抵御临床症状。进行了一项传播实验及一次重复实验，每次实验均设有六组商品肉鸡。在出雏日（n = 30）或15日龄（n = 20）时，每组半数禽类接种IBV H120疫苗（H120组）或强毒IBV M41（M41组），另一半进行 mock感染，从而使每组另一半禽类接触感染。记录鼻分泌物，并检测抗体反应和病毒排出情况。为测定临床保护效果，接种四周后，所有组的禽类均用IBV M41进行攻毒。通过确定繁殖率（R；一只感染禽类引起的平均接触感染数）来量化病毒传播。除H120组的一只禽类外，所有接触感染的禽类均感染了IBV H120或IBV M41。几乎所有接触感染IBV H120或IBV M41的禽类在随后用IBV M41攻毒后均能抵御临床症状。IBV H120疫苗及IBV M41的R的95%置信区间（CI）下限均显著<1。对于IBV H120和IBV M41，出雏日接种后的95%CI为[2.1 - 无穷大]，15日龄接种后的95%CI为[1.8 - 无穷大]。这一发现表明IBV H120疫苗能够在肉鸡中广泛传播。这意味着该疫苗株可能会在家禽群体中成为地方流行毒株。这还意味着，即使在喷雾接种疫苗时并非所有禽类都接种了疫苗，但由于疫苗在鸡群中的传播能力，它们很可能在随后感染田间病毒后抵御临床症状。
