美国近期暴发新城疫疫情流行特点分析

Analysis on the Epidemiological Characteristics of Newcastle Disease Outbreak in the United States

2018年5月,美国加利福尼亚州在南部地区发病散养鸡中检测到新城疫病毒强毒株。这是美国自2003年以来,首次出现新城疫病毒强毒株感染的报道。该病传播速度快、致死率高。截至2019年5月24日,美国农业部已在加利福尼亚州、犹他州和亚利桑那州共确诊新城疫疫情425起,其中加利福尼亚州423起,犹他州、亚利桑那州各1起。病原学分析显示,此次流行的新城疫病毒属于基因Vb亚型。初步遗传分析表明,本次疫情暴发为单点传入并造成二次扩散,但病毒暴发的起源仍未确定。病例对照研究表明,禽群数量大小、观赏鸟、禽群中公鸡高占比、与野鸟接触等是病毒感染的风险因素。美国政府已采取包括限制移动易感动物、扑杀暴露动物、提升饲养场生物安全水平、避免家禽与野禽接触以及家禽与其他传染源接触、加强监测筛查和流行病学跟踪支持等等一系列举措来控制新城疫疫情的传播。但该病毒仍具有持续性威胁,或有进一步传播的可能,对于该疫病的防控和监测工作仍在继续。

On May 16,2018,a strain of virulent Newcastle disease virus(NDV)was detected in free-range chickens in southern California,which was the first report in the United States since 2003. As the disease could spread rapidly with high fatality rate,425 cases had been confirmed in California,Utah and Arizona by United States Department of Agriculture(USDA)till May 24,2019,including 423 cases in California,1 case in Utah and in Arizona respectively. The pathogen analysis showed that,current NDV was classified into gene subtype Vb. The outbreak was considered as the secondary spread caused by single-point introduction in accordance with preliminary genetic analysis,however,the virus source was still unclear. Further,it was indicated that,by comparing and studying all cases,the risk factors of infection mainly included flock size,pet birds,high proportion of cocks in poultry flocks,contacting with wild birds,etc. To control the outbreak,a series of measures were adopted by USDA,including isolating susceptible animals,culling exposed animals,strengthening surveillance and screening, supporting epidemiological tracking,avoiding any contact with wild birds or other infectious sources,and improving the level of bio-safety in farms. However,there was still some ongoing threats,or the disease had the possibility to further spread,so the prevention and control or surveillance of the disease was still continuing.