High number of HPAI H5 virus infections and antibodies in wild carnivores in the Netherlands, 2020–2022

In October 2020, a new lineage of a clade 2.3.4.4b HPAI virus of the H5 subtype emerged in Europe, resulting in the largest global outbreak of HPAI to date, with unprecedented mortality in wild birds and poultry. The virus appears to have become enzootic in birds, continuously yielding novel HPAI virus variants. The recently increased abundance of infected birds worldwide increases the probability of bird–mammal contact, particularly in wild carnivores. Here, we performed molecular and serological screening of over 500 dead wild carnivores and sequencing of RNA positive materials. We show virological evidence for HPAI H5 virus infection in 0.8%, 1.4%, and 9.9% of animals tested in 2020, 2021, and 2022 respectively, with the highest proportion of positives in foxes, polecats and stone martens. We obtained near full genomes of 7 viruses and detected PB2 amino acid substitutions known to play a role in mammalian adaptation in three sequences. Infections were also found in without neurological signs or mortality. Serological evidence for infection was detected in 20% of the study population. These findings suggests that a high proportion of wild carnivores is infected but undetected in current surveillance programmes. We recommend increased surveillance in susceptible mammals, irrespective of neurological signs or encephalitis.

2020年10月，H5亚型高致病性禽流感（Highly Pathogenic Avian Influenza, HPAI）病毒进化分支2.3.4.4b的一个新谱系在欧洲出现，引发了迄今为止全球规模最大的高致病性禽流感疫情，对野生鸟类与家禽造成了史无前例的致死率。该病毒现已在鸟类种群中形成地方性流行态势，持续不断产生新型高致病性禽流感病毒变体。近期全球范围内受感染鸟类的种群数量显著增加，提升了鸟类与哺乳动物的接触风险，这一现象在野生食肉动物群体中尤为突出。
本研究对500余只死亡的野生食肉动物开展了分子及血清学筛查，并对RNA检测呈阳性的样本进行了测序。结果显示，2020年、2021年及2022年的受检动物中，H5亚型高致病性禽流感病毒感染的病毒学阳性率分别为0.8%、1.4%与9.9%，其中狐狸、艾鼬和石貂的阳性检出率最高。我们成功获取了7株病毒的近乎全长基因组序列，并在3条序列中检测到了已知可影响哺乳动物适应性的PB2蛋白氨基酸替换位点。部分感染个体未表现出明显神经症状或死亡症状。此外，在20%的研究对象中检测到了感染相关的血清学阳性证据。
上述研究结果表明，当前的监测体系中存在大量未被发现的野生食肉动物感染病例。据此，我们建议针对易感哺乳动物群体加强监测工作，无需考虑其是否表现出神经症状或脑炎症状。