Pathogenicity of three H9N2 avian influenza viruses of Guangxi sparrow origin to SPF chickens

Abstract

[Objective] To clarify the pathogenicity of H9N2 avian influenza virus (AIV) of sparrow origin to chickens, which was helpful to understand the role of sparrows in the ecological chain of H9N2 subtype AIV transmission, and it also had important significance for scientific prevention and control of the outbreak of H9N2 subtype AIV.

[Method] Three Guangxi H9N2 AIV virus of sparrow origin with HA genes belonging to different evolutionary branches were selected for SPF chicken pathogenicity test. A total of 84 4-week SPF chickens were randomly divided into 4 groups (blank control group and 3 infection groups). In each infection group, 16 SPF chickens were infected nasally with 100 μL virus which has been diluted to 10 ⁶ EID ₅₀/100 μL, the remaining 5 SPF chickens were placed in each infection group as blank contact group after 24 h of infection. Clinical symptoms and pathological changes of the chickens were observed after infection. Tissues were collected at different time points to make pathological sections, virus titers and distribution in different organs were detected.

[Results] Three H9N2 subtype AIV of sparrow origindid not have multiple basic amino acid insertions at the cleavage site of HA protein, showing RSSR↓GLF, which was consistent with the typical molecular characteristics of low pathogenicity AIV (LPAIV). The median infective dose (EID ₅₀) of chicken embryos ranged from 10 ^-6.0/0.2 mL to 10 ^-6.8/0.2 mL, and median lethal dose (ELD ₅₀) ranged from 10 ^-6.8/0.2 mL to 10 ^-7.2/0.2 mL. All the three H9N2 AIV could directly infect SPF chickens, and there were some differences in the virus titer and distribution of the virus in different organs. The SPF chickens did not show any obvious clinical symptoms and death, but there was a certain degree of congestion and bleeding in the trachea and lung of the upper respiratory tract, tracheal ciliary detachment, inflammatory lymphocyte infiltration and other changes after infection. The detoxification period of three H9N2 subtype AIV of sparrow origin infected SPF chickens was mainly between 1 d and 7 d, and they could directly infect chickens and detoxify without in vivo adaptation. There were some differences in the replication ability of the three sparrows of H9N2 AIV in the organs of SPF chickens, and they could replicate effectively in the trachea and lung, while no corresponding virus was detected in the liver, brain, pancreas, thymus, heart, cecum tonsil and bursa.

[Conclusion] H9N2 subtype AIV of sparrow origin could directly infect chickens and has the potential of horizontal transmission among chickens, suggesting that relevant protective measures should be taken in poultry breeding, transportation and marketing to cut off the transmission routes of AIV between wild birds and poultry, so as to reduce the economic losses caused by avian influenza outbreaks.

Abstract

摘要: 【目的】 明确麻雀源H9N2亚型禽流感病毒 (AIV) 对鸡群的致病性, 既有利于了解麻雀在H9N2亚型AIV传播 生态链中的作用, 对科学防控H9N2亚型AIV的暴发流行也具有重要意义。 【方法】选取3株HA基因处于不同进化分支 的广西麻雀源H9N2亚型AIV进行SPF鸡致病性试验, 将84羽4周龄SPF鸡随机均分为4组 (空白对照组和3个感染组)。 感染组每组以100 μL稀释至10 ⁶ EID ₅₀/100 μL的病毒液经鼻腔感染16羽SPF鸡, 于病毒感染24 h后分别在各感染组放 人剩余的5羽SPF鸡作为空白接触组, 感染后观察鸡群的临床症状及剖检病理变化, 在不同时间点采集器官组织制作 病理切片并检测不同器官中的病毒滴度及分布情况。 【结果】3株麻雀源H9N2亚型AIV在HA蛋白裂解位点处不存在 多个碱性氨基酸插人现象, 表现为RSSR↓GLF, 符合低致病性AIV (LPAIV) 的典型分子特征; 对鸡胚的半数感染量 (EID ₅₀)在 10 ^-6.0/0.2 mL~10 ^-6.8/0.2 mL, 半数致死量(ELD ₅₀)在 10 ^-6.8/0.2 mL~10 ^-7.2/0.2 mL。3株H9N2亚型AIV均可直接感 染SPF鸡, 且病毒在不同器官中的滴度及分布存在一定差异;感染SPF鸡后均未表现出明显的临床症状和死亡现象, 但在上呼吸道的气管及肺脏出现一定程度的充血和出血、气管纤毛脱落及炎性淋巴细胞浸润等病变。3株麻雀源 H9N2亚型AIV感染SPF鸡后的排毒期主要介于第1~7 d, 且能不经体内适应而直接感染鸡群并排毒;3株麻雀源H9N2 亚型AIV在SPF鸡各器官中的复制能力存在一定差异, 可在气管和肺脏中进行有效复制, 而在肝脏、脑、胰腺、胸腺、心 脏、盲肠扁桃体及法氏囊中均未检测到对应的病毒。 【结论】麻雀源H9N2亚型AIV可直接感染鸡群且具有在鸡群间水 平传播的潜在风险, 提示在家禽饲养、运输及销售等环节要做好相关的防护措施, 切断AIV在野鸟与家禽间的传播途 径, 减少禽流感暴发造成的经济损失。