An outbreak caused by H7N3 low pathogenicity avian influenza virus (LPAIV) occurred in commercial turkey farms in the states of North Carolina (NC) and South Carolina (SC), United States in March of 2020. Subsequently, H7N3 high pathogenicity avian influenza virus (HPAIV) was detected on a turkey farm in SC. The infectivity, transmissibility, and pathogenicity of the H7N3 HPAIV and two LPAIV isolates, including one with a deletion in the neuraminidase (NA) protein stalk, were studied in turkeys and chickens. High infectivity [<2 log₁₀ 50% bird infectious dose (BID₅₀)] and transmission to birds exposed by direct contact were observed with the HPAIV in turkeys. In contrast, the HPAIV dose to infect chickens was higher than for turkeys (3.7 log₁₀ BID₅₀), and no transmission was observed. Similarly, higher infectivity (<2–2.5 log₁₀ BID₅₀) and transmissibility were observed with the H7N3 LPAIVs in turkeys compared to chickens, which required higher virus doses to become infected (5.4–5.7 log₁₀ BID₅₀). The LPAIV with the NA stalk deletion was more infectious in turkeys but did not have enhanced infectivity in chickens. These results show clear differences in the pathobiology of AIVs in turkeys and chickens and corroborate the high susceptibility of turkeys to both LPAIV and HPAIV infections.

中文翻译：

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2020年美国爆发的H7N3低致病性禽流感病毒和高致病性禽流感病毒的病理学在火鸡和鸡之间存在差异

2020年3月，美国北卡罗来纳州（NC）和南卡罗来纳州（SC）的商业火鸡养殖场爆发了由H7N3低致病性禽流感病毒（LPAIV）引起的疫情。随后，H7N3高致病性禽流感病毒（H7N3高致病性禽流感病毒（ HPAIV) 在南卡罗来纳州的一个火鸡场被发现。在火鸡和鸡身上研究了 H7N3 HPAIV 和两种 LPAIV 分离株的传染性、传播性和致病性，其中包括一种神经氨酸酶 (NA) 蛋白柄缺失的分离株。在火鸡中观察到高传染性 [<2 log ₁₀ 50% 禽类感染剂量 (BID _{50 )] 和通过直接接触暴露于禽类的传播。}相比之下，感染鸡的 HPAIV 剂量高于火鸡（3.7 log ₁₀ BID₅₀ )，并且没有观察到透射。同样，与鸡相比，在火鸡中观察到 H7N3 LPAIV 具有更高的传染性（<2-2.5 log ₁₀ BID _{50 ）和传播性，鸡需要更高的病毒剂量才能被感染（5.4-5.7 log 10} BID ₅₀）。具有NA茎缺失的LPAIV在火鸡中更具传染性，但在鸡中没有增强的传染性。这些结果表明火鸡和鸡中 AIV 的病理生物学存在明显差异，并证实了火鸡对 LPAIV 和 HPAIV 感染的高度易感性。