Kurukulasuriya Shanika, Ahmed Khawaja Ashfaque, Ojkic Davor, Gunawardana Thushari, Goonewardene Kalhari, Gupta Ashish, Chow-Lockerbie Betty, Popowich Shelly, Willson Philip, Tikoo Suresh K, Gomis Susantha
Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada.
Animal Health Laboratory, University of Guelph, P.O. Box 3612, Guelph, ON N1H 6R8, Canada.
Vaccine. 2017 Feb 7;35(6):882-888. doi: 10.1016/j.vaccine.2017.01.005. Epub 2017 Jan 12.
Chickens are commonly processed around 35-45days of age in broiler chicken industry hence; diseases that occur at a young age are of paramount economic importance. Early age infection with infectious bursal disease virus (IBDV) results in long-lasting immunosuppression and profound economic losses. To our knowledge, this is the first study comparing the protection efficacy of modified live (MdLV) IBDV and herpesvirus turkey (HVT)-IBDV vaccines against early age variant IBDV (varIBDV) infection in chicks. Experiments were carried out in IBDV maternal antibody (MtAb) positive chicks (n=330), divided into 6 groups (n=50-60/group), namely Group 1 (saline), Group 2 (saline+varIBDV), Group 3 (HVT-IBDV), Group 4 (HVT-IBDV+varIBDV), Group 5 (MdLV) and Group 6 (MdLV+varIBDV). HVT-IBDV vaccination was given via the in ovo route to 18-day-old embryonated eggs. MdLV was administered via the subcutaneous route in day-old broilers. Group 2, Group 4 and Group 6 were orally challenged with varIBDV (SK-09, 3×10 EID) at day 6 post-hatch. IBDV seroconversion, bursal weight to body weight ratio (BBW) and bursal histopathology were assessed at 19 and 35days of age. Histopathological examination at day 19 revealed that varIBDV-SK09 challenge caused severe bursal atrophy and lower BBW in HVT-IBDV but not in MdLV vaccinated chicks. However by day 35, all challenged groups showed bursal atrophy and seroconversion. Interestingly, RT-qPCR analysis after varIBDV-SK09 challenge demonstrated an early (9days of age) and significantly high viral load (∼5744 folds) in HVT-IBDV vaccinated group vs unvaccinated challenged group (∼2.25 folds). Furthermore, flow cytometry analysis revealed inhibition of cytotoxic CD8 T-cell response (CD44-downregulation) and decreased splenic lymphocytes counts in chicks after HVT-IBDV vaccination. Overall, our data suggest that MdLV delays varIBDV pathogenesis, whereas, HVT-IBDV vaccine is potentially immunosuppressive, which may increase the risk of early age varIBDV infection in broilers.
在肉鸡行业中，鸡通常在35至45日龄左右进行加工处理，因此，幼龄期发生的疾病具有至关重要的经济意义。幼龄期感染传染性法氏囊病病毒（IBDV）会导致长期的免疫抑制和巨大的经济损失。据我们所知，这是第一项比较改良活（MdLV）IBDV疫苗和火鸡疱疹病毒（HVT）-IBDV疫苗对雏鸡幼龄期变异IBDV（varIBDV）感染保护效果的研究。实验在IBDV母源抗体（MtAb）阳性的雏鸡（n = 330）中进行，分为6组（每组n = 50 - 60），即第1组（生理盐水）、第2组（生理盐水+varIBDV）、第3组（HVT-IBDV）、第4组（HVT-IBDV+varIBDV）、第5组（MdLV）和第6组（MdLV+varIBDV）。HVT-IBDV疫苗通过卵内接种途径接种于18日龄的胚胎蛋。MdLV通过皮下途径接种于1日龄的肉鸡。第2组、第4组和第6组在出壳后第6天经口用varIBDV（SK-09，3×10 EID）进行攻毒。在19日龄和35日龄时评估IBDV血清转化、法氏囊重量与体重比（BBW）以及法氏囊组织病理学。19日龄时的组织病理学检查显示，varIBDV-SK09攻毒在HVT-IBDV疫苗接种的雏鸡中导致严重的法氏囊萎缩和较低的BBW，但在MdLV疫苗接种的雏鸡中未出现。然而到35日龄时，所有攻毒组均出现法氏囊萎缩和血清转化。有趣的是，varIBDV-SK09攻毒后的RT-qPCR分析表明，与未接种疫苗的攻毒组（约2.25倍）相比，HVT-IBDV疫苗接种组在早期（9日龄）病毒载量显著较高（约5744倍）。此外，流式细胞术分析显示HVT-IBDV疫苗接种后雏鸡细胞毒性CD8 T细胞反应受到抑制（CD44下调）且脾脏淋巴细胞计数减少。总体而言，我们的数据表明MdLV可延缓varIBDV发病机制，而HVT-IBDV疫苗具有潜在的免疫抑制作用，这可能会增加肉鸡幼龄期varIBDV感染的风险。
