Live H5N1 avian influenza virus found in fetal bovine serum raises biosafety concerns

Researchers at Cornell University have identified live H5N1 virus in commercial fetal bovine serum, prompting a review of biosafety protocols amid potential laboratory risks.

Cornell University researchers have reported finding live H5N1 avian influenza virus in a commercial batch of fetal bovine serum, a widely used growth supplement in cell culture, raising a biosafety issue for laboratories and biomanufacturers rather than a food-safety concern.

According to the CDC’s journal Emerging Infectious Diseases, the lot was identified during routine screening at Cornell’s Animal Health Diagnostic Centre in February 2025. Sequencing showed the virus was the highly pathogenic H5N1 clade 2.3.4.4b, genotype B3.13, the strain linked to the US dairy-cattle outbreak that began in March 2024.

The serum was pooled from animals in Pennsylvania, Kansas, Nebraska, South Carolina and California, illustrating how a single infected source can enter a distributed supply chain. Cornell later tested individual samples from slaughterhouses in California and Texas and found one positive result among 768 specimens, suggesting only low-level and sporadic contamination.

The reassuring finding is that heating serum to 56C for 30 minutes inactivated the virus in laboratory tests, matching standard heat-inactivation practice used by many suppliers. That said, heat treatment is not universal, because it can damage some growth factors needed by sensitive cell lines.

The study does not show that anyone was infected, but it may prompt diagnostics labs and biosafety committees to review serum sourcing and heat-treatment protocols.

Reference: Rebelo AR, Butler E, Nunez E, Cronk B, Powers J, Laverack M, et al. Isolation of Highly Pathogenic Avian Influenza A(H5N1) Virus from Fetal Bovine Serum, United States, 2025. Emerg Infect Dis. 2026;32(8):1323-1326. https://doi.org/10.3201/eid3208.260077