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Scientists at the National Institutes of Health (NIAID) have found that heat treatment can significantly reduce the amount of infectious H5N1 virus in raw milk, but small amounts of the virus may remain under certain conditions. This finding is important in light of reported outbreaks of the H5N1 virus in dairy cows in the United States.

美国国立卫生研究院（NIAID）的科学家们发现，热处理可大大降低生牛奶中传染性 H5N1 病毒的含量，但在某些条件下仍会残留少量病毒。据报道，美国奶牛中爆发了 H5N1 病毒疫情，这一发现非常重要。

Studies have shown that heating raw milk can significantly reduce the amount of H5N1 virus, but it may still remain. Despite the outbreak of cattle flu in the United States, the FDA's ongoing assessment has concluded that commercial milk is safe.

研究表明，加热生奶可大大降低 H5N1病毒的含量，但仍有可能残留。尽管美国爆发了牛流感疫情，但食品及药物管理局正在进行的评估认为，商业牛奶是安全的。

Laboratory experiments show that the amount of infectious H5N1 influenza virus in raw milk drops rapidly after being heated. The research was conducted by scientists at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH).

实验室实验表明，加热处理后，生牛奶中传染性 H5N1 流感病毒的数量迅速下降。这项研究由美国国立卫生研究院（NIH）下属的国立过敏与传染病研究所（NIAID）的科学家进行。

However, low levels of infectious virus were still detectable in raw milk samples with elevated viral loads after treatment at 72 degrees Celsius (161.6 degrees Fahrenheit) for 15 seconds, one of the standard pasteurization methods used by the dairy industry. However, the study authors stressed that their findings reflect experimental conditions in a laboratory setting and are not identical to the large-scale industrial raw milk pasteurization process. The results were published June 13 in the New England Journal of Medicine.

然而，在 72摄氏度（161.6华氏度）的条件下处理 15 秒（这是乳制品行业使用的标准巴氏杀菌法之一），病毒含量较高的生奶样本中仍能检测到少量传染性病毒。不过，该研究的作者强调，他们的发现反映的是实验室环境下的实验条件，与大规模工业化的生奶巴氏杀菌过程并不完全相同。研究结果于 6 月 13 日发表在《新英格兰医学杂志》上。

In late March 2024, U.S. officials reported an outbreak of a highly pathogenic avian influenza virus, called HPAI H5N1, in dairy cows in Texas. To date, 95 herds in 12 states have been affected, and three human cases have been found in farm workers with conjunctivitis. While the virus has not so far genetically demonstrated the ability to spread between people, public health officials are closely monitoring dairy cows as part of pandemic preparedness efforts.

2024 年 3 月下旬，美国官员报告在得克萨斯州的奶牛中爆发了名为高致病性禽流感 H5N1 的高致病性禽流感病毒。迄今为止，已有 12 个州的 95 个牛群受到影响，在患有结膜炎的农场工人中发现了 3 例人感染病例。虽然到目前为止，该病毒还没有在基因上显示出在人与人之间传播的能力，但公共卫生官员正在密切监测奶牛的情况，作为大流行病防备工作的一部分。

Given limited data on the susceptibility of avian influenza viruses to pasteurization methods used by the dairy industry, scientists at NIAID's Rocky Mountain Laboratories sought to quantify the stability of H5N1 viruses in raw milk when tested at different intervals at 63°C (145.4°F) and 72°C, the temperatures most commonly used in commercial dairy pasteurization processes. The scientists isolated highly pathogenic avian influenza H5N1 viruses from the lungs of a mountain lion that died in Montana. They then mixed these viral isolates with samples of raw, unpasteurized milk and heat-treated the milk at 63°C and 72°C for different periods of time. The samples were then cultured and tested to determine whether, and if so, how much live virus remained.

鉴于有关禽流感病毒对乳制品行业使用的巴氏杀菌法的敏感性的数据有限，NIAID 洛基山实验室的科学家们试图量化生牛奶中 H5N1 病毒在 63℃（华氏 145.4 度）和 72℃（商业乳制品巴氏杀菌过程中最常见的温度）的不同时间间隔下进行检测时的稳定性。科学家们从蒙大拿州一头死亡山狮的肺部分离出了高致病性禽流感 H5N1 病毒。然后，他们将这些病毒分离物与未经巴氏杀菌的生牛奶样本混合，并在 63℃ 和 72℃ 下对牛奶进行不同时间段的热处理。然后对样本进行细胞培养和检测，以确定是否残留有活病毒，如果有，残留多少。

They found that a temperature of 63°C produced a significant reduction in infectivity levels of H5N1 virus (1010-fold) within 2.5 minutes, and noted that 30 minutes of standard bulk pasteurization eliminated infectious virus. At 72°C, they observed a 104-fold reduction in infectious virus within 5 seconds, however, in one of three samples, very low levels of infectious virus were still detected after heat treatment for up to 20 seconds. The authors noted: "This finding suggests that relatively low but detectable amounts of H5N1 virus may still be present in milk after heating at 72°C for 15 seconds if initial viral levels are sufficiently high."

他们发现，63℃ 的温度可在 2.5 分钟内使 H5N1 病毒的感染性水平显著下降（1010 倍），并指出 30 分钟的标准散装巴氏杀菌可消除感染性病毒。在 72℃下，他们观察到传染性病毒在 5 秒钟内减少了104 倍，然而，在三个样品中，有一个样品在加热处理长达 20 秒钟后仍检测到极少量的传染性病毒。作者指出："这一发现表明，如果初始病毒水平足够高，72℃加热 15 秒后，牛奶中仍有可能存在相对少量但可检测到的 H5N1 病毒。"

The scientists emphasize that their measurements reflect experimental conditions and should be replicated by direct measurements of infected milk in commercial pasteurization facilities, and that no conclusions should be drawn about the safety of the U.S. milk supply. In addition, a limitation of their study was the use of raw milk samples spiked with H5N1 virus, and raw milk from cows infected with H5N1 influenza may have a different composition or contain cell-associated virus, which could affect the thermal effect. The authors conclude that while highly pathogenic avian influenza H5N1 viruses have caused enteric infections in several mammals, it remains unknown whether ingestion of live H5N1 virus in raw milk can cause illness in humans.

科学家们强调，他们的测量结果反映的是实验条件，应在商业巴氏杀菌设备中对受感染牛奶进行直接测量后再进行复制，不应据此对美国牛奶供应的安全性得出任何结论。此外，他们研究的局限性在于使用了添加 H5N1 病毒的生乳样本，而来自感染 H5N1 流感奶牛的生乳可能具有不同的成分或含有细胞相关病毒，这可能会影响热效应。作者总结说，虽然高致病性禽流感 H5N1 病毒已在几种哺乳动物身上发生过肠道感染，但摄入生牛奶中的活 H5N1 病毒是否会导致人类患病仍是未知数。

To date, the U.S. Food and Drug Administration (FDA) has concluded that all evidence continues to indicate that the commercial milk supply is safe. While laboratory benchtop studies provide important, useful information, their limitations pose challenges for extrapolating to real-world commercial processing and pasteurization. The FDA conducted an initial survey of 297 retail dairy products collected at retail locations in 17 states and representing products produced at 132 processing sites in 38 states. All samples were negative for the virus. These results highlight the opportunity for additional studies to closely replicate real-world conditions. The FDA is working with the U.S. Department of Agriculture on pasteurization validation studies, including the use of homogenizers and continuous-flow pasteurizers. We will share additional results as they become available.

迄今为止，美国食品和药物管理局（FDA）的结论是，所有证据仍然表明商业牛奶供应是安全的。虽然实验室台式研究提供了重要、有用的信息，但其局限性对推断现实世界中的商业加工和巴氏杀菌提出了挑战。美国食品和药物管理局对在 17 个州的零售点收集的 297 个零售乳制品进行了初步调查，并代表了在 38 个州的 132 个加工点生产的产品。结果发现，所有样品中的病毒均为阴性。这些结果突出表明，有机会进行更多的研究，以密切复制现实世界的条件。FDA 正在与美国农业部合作开展巴氏杀菌验证研究，包括使用均质器和连续流巴氏杀菌器。一旦有了更多结果，我们将立即公布。

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