Animal Science, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia,
School of Veterinary Medicine, Wollo University, Dessie, Ethiopia.
Avian Dis. 2023 Jun;67(2):160-169. doi: 10.1637/aviandiseases-D-22-00050.
Mass vaccination against infectious laryngotracheitis virus (ILTV) in drinking water can result in variable initial vaccine take. Partial initial vaccine coverage of 20% with an Australian ILT vaccine (A20) previously resulted in significant protection against virulent ILTV challenge. This follow-up study used the international Serva ILT vaccine strain in a factorial design testing four levels of vaccination coverage (0%, 10%, 20%, or 100% of chicks eye-drop vaccinated with the live vaccine at 7 days of age) and three levels of ILTV challenge (no challenge or challenge at 7 or 21 days postvaccination [DPV]). The increase in ILTV load in choanal cleft swabs detected by qPCR after challenge was significantly reduced by 20% and 100% but not by 10% vaccination coverage. Vaccination reduced weight gain in unchallenged birds. Daily weight gain of birds was not affected by ILTV challenge at 7 DPV in any group, but following challenge at 21 DPV, it was significantly reduced in unvaccinated and 10% vaccinated groups relative to 20% and 100% vaccinated groups. Vaccination of 20% of the chickens provided substantial but incomplete protection (protective index range 44%-70%) against the severity of clinical signs and mortality following challenge while 10% vaccination coverage provided limited or no protection. Clinical signs were more severe and appeared earlier following challenge at 21 DPV than at 7 DPV. Within the vaccination treatments, eye-drop-vaccinated birds were better protected than their in-contact cohorts. In conclusion, partial vaccination of 20%, but not 10% of chickens, induced substantial protection against subsequent challenge. However, the attendant risks of reduced protection against early challenge and the possible reversion to virulence of vaccine virus when transmitted to unvaccinated chickens make it essential that 100% initial vaccine take be the goal of mass vaccination programs.
饮水免疫传染性喉气管炎病毒（ILTV）疫苗可导致初始疫苗接种效果的差异。先前使用澳大利亚传染性喉气管炎疫苗（A20）进行部分初始疫苗接种，覆盖率为 20%，可显著预防强毒 ILTV 攻毒。本后续研究采用国际 Serva ILT 疫苗株，采用因子设计检测四种疫苗接种覆盖率（0%、10%、20%或 100%，7 日龄雏鸡经滴眼接种活疫苗）和三种 ILTV 攻毒水平（无攻毒或攻毒于接种后 7 或 21 天）。攻毒后通过 qPCR 检测到的鼻后腔拭子中的 ILTV 载量增加，经 20%和 100%疫苗接种显著降低，但 10%疫苗接种覆盖率无显著降低。疫苗接种可减少未攻毒鸡的体重减轻。在任何组中，7 日龄攻毒均不影响未攻毒鸡的日增重，但在 21 日龄攻毒后，与 20%和 100%疫苗接种组相比，未接种和 10%疫苗接种组的鸡体重减轻显著。对 20%的鸡进行疫苗接种可提供针对临床症状严重程度和攻毒后死亡率的实质性但不完全保护（保护指数范围为 44%-70%），而 10%的疫苗接种覆盖率提供有限或无保护。与 7 日龄攻毒相比，21 日龄攻毒后的临床症状更严重且更早出现。在疫苗接种处理中，滴眼接种的鸡比与其接触的鸡群得到更好的保护。总之，20%的鸡进行部分疫苗接种，但不是 10%的鸡，可诱导对后续攻毒的实质性保护。然而，当疫苗病毒传播到未接种鸡时，早期攻毒保护降低和疫苗病毒可能返祖为强毒的风险，使得 100%初始疫苗接种覆盖率成为群体免疫接种计划的必要目标。
