В лабораторной сыворотке выявлен живой вирус птичьего гриппа H5N1

Live H5N1 Was Isolated from Fetal Bovine Serum in a Finding That Puts Laboratory Biosafety Under New Scrutiny Researchers at Cornell University isolated live, infectious H5N1 avian influenza virus from a commercial lot of fetal bovine serum, the growth supplement used in cell culture laboratories worldwide, in a report published in the August issue of the CDC journal Emerging Infectious Diseases. The finding matters to a specific audience, and it is worth stating plainly who that is. This is a laboratory biosafety and manufacturing quality-control story, not a consumer exposure story. No pasteurized dairy product, retail meat item, or medical treatment is implicated. The people whose practices may change are diagnosticians, cell culture technicians, biomanufacturing staff, and the institutional biosafety committees that write their protocols. The detection also carries one immediately reassuring result. Heating the serum to 56 degrees Celsius for 30 minutes, a step already built into many commercial serum products and lab protocols, inactivated the virus in the authors' experiments. Routine Screening at Cornell Caught the Contaminated Lot The lot arrived at the Virology Laboratory of the Cornell Animal Health Diagnostic Center in February 2025 for routine extraneous agents testing, a screening requirement under federal regulations governing biological products of animal origin. It was not submitted because anyone suspected contamination. Sequencing identified the virus as highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b, genotype B3.13, the lineage that has been circulating in U.S. dairy cattle since March 2024. As of mid-December 2025, more than 1,084 herds in 19 states had been affected, with most concentrated in California. The tested lot was a pool of samples collected in five states: Pennsylvania, Kansas, Nebraska, South Carolina, and California. That detail is the load-bearing one for anyone assessing risk in their own supply chain, and it is addressed below. Serum Is a Pooled Product, and That Matters Fetal bovine serum is collected from bovine fetuses at slaughterhouses and is, in the paper's own framing, the most frequently used growth supplement in cell culture media. It is commonly added to basal media at concentrations of about 5-10% and supports a wide range of cell types in academic research, pharmaceutical development, and biomanufacturing. Because it is pooled from many animals, a single infected donor can contribute a large amount that is subsequently widely distributed. The Cornell team followed the positive lot with broader testing, screening individual serum samples collected at slaughterhouses in California and Texas, 384 from each state. Of those 768 samples, one tested positive by real-time reverse transcription PCR, at a cycle threshold of 35, indicating a low viral load. The authors interpret that pattern as consistent with sporadic viremia in infected lactating dairy cattle, allowing the virus to reach tissues beyond the udder, including, on rare occasions, the fetus. Follow-up testing of 13 additional bottles from the same original lot, eight of them not heat-inactivated and five heat-inactivated, is documented in a summary table accompanying the paper, using virus isolation in two cell lines, embryonated eggs, and PCR. Detection was infrequent even by PCR, and attempts to confirm virus isolation at USDA's National Veterinary Services Laboratories were not successful, which the authors take as evidence of very low viral loads in the pooled lot. Heat Treatment Cleared the Virus in Laboratory Tests The inactivation experiment is the part with an actionable conclusion. Serum aliquots were spiked with bovine H5N1 at high titer and heated. The authors report that heating at 56 degrees Celsius for 30 minutes inactivated the virus, and they conclude that although finding a zoonotic virus in serum raises biosafety concerns for diagnostic testing of bovine serum and for laboratory procedures using it, "heat treatment of FBS seems to be efficient in inactivating the virus" and could serve as a safety precaution. That temperature and duration are not novel. Commercial suppliers, including ATCC, publish 56 degrees for 30 minutes as the standard heat-inactivation protocol, and heat-inactivated serum is sold as a distinct product line. The complication is that heat inactivation is not a universal practice because suppliers caution that it is unnecessary for many cell lines and can degrade heat-labile growth factors that some cells require. The result also aligns with earlier work. Heat inactivation of H5N1 in raw cow's milk was examined in a report in the New England Journal of Medicine, part of a broader body of research into how thermal treatment affects this virus in bovine-origin material. Consumers Are Not the Audience for This Finding Several limitations go hand in hand with the headline result. This is a single documented lot, identified through routine surveillance rather than through any adverse event. No laboratory-acquired infection has been reported in connection with it. The authors note that their findings and conclusions do not necessarily reflect the official positions of the agencies involved, and that one co-author is affiliated with USDA's Animal and Plant Health Inspection Service. The paper does not establish how often serum lots are contaminated because it was not designed to. Nor does it demonstrate that anyone has been infected through this route. It documents that a live virus survived in a commercial biological product and that a widely available treatment step neutralized it under laboratory conditions. What laboratories and biomanufacturers may reasonably reconsider is whether their current serum sourcing, screening, and heat-treatment decisions account for a pathogen that was not circulating in U.S. cattle three years ago. Institutional biosafety committees, not individual bench scientists, are typically the right level for that review. Facilities working with bovine-origin material should confirm what their supplier tests for and whether their lots are heat-inactivated. The broader surveillance question remains open. Continued monitoring of H5N1 in dairy cattle and of the animal-origin products the herds feed into is tracked through the CDC journal's influenza research collection. Whether contamination of serum proves to be rare or more common than a single lot suggests will depend on testing that has not yet been reported. Key Questions Answered What did researchers find? Live, infectious H5N1 avian influenza virus was isolated from a commercial lot of fetal bovine serum submitted to the Cornell Animal Health Diagnostic Center for routine screening. Sequencing identified genotype B3.13. Is this a risk to consumers? No consumer product is implicated. Fetal bovine serum is a laboratory and biomanufacturing reagent, not a food ingredient, and the report concerns laboratory biosafety rather than dietary exposure. Did anyone get sick from it? No laboratory-acquired infection has been reported in connection with this lot. The detection came from routine testing, not from an illness investigation. Does heat treatment solve the problem? In these experiments, heating serum to 56 degrees Celsius for 30 minutes inactivated the virus. That protocol is already standard for heat-inactivated serum products, though heat inactivation is not used for every cell line. How could a virus reach a fetal sample? The authors suggest sporadic bloodstream infection in lactating dairy cattle can allow the virus to reach tissues beyond the udder, including, in rare cases, the fetus. How common is contamination? Unknown. The study documents one positive lot and one positive individual sample among 768 samples tested at slaughterhouses in two states. It was not designed to estimate overall prevalence. Who should act on this? Institutional biosafety committees, diagnostic laboratories and biomanufacturers using bovine-origin material, who may want to confirm supplier testing and heat-treatment status for their serum lots. Published by Medicaldaily.com