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Review 2: "Pasteurisation Temperatures Effectively Inactivate Influenza A Viruses in Milk"

Reviewers found this preprint reliable and that the conclusions were supported by the data. 

Published onJul 25, 2024
Review 2: "Pasteurisation Temperatures Effectively Inactivate Influenza A Viruses in Milk"
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Pasteurisation temperatures effectively inactivate influenza A viruses in milk
Pasteurisation temperatures effectively inactivate influenza A viruses in milk
Description

Abstract In late 2023 an H5N1 lineage of high pathogenicity avian influenza virus (HPAIV) began circulating in American dairy cattle1. Concerningly, high titres of virus were detected in cows’ milk, raising the concern that milk could be a route of human infection. Cows’ milk is typically pasteurised to render it safe for human consumption, but the effectiveness of pasteurisation on influenza viruses in milk was uncertain. To assess this, we evaluated heat inactivation in milk for a panel of different influenza viruses. This included human and avian influenza A viruses (IAVs), an influenza D virus that naturally infects cattle, and recombinant IAVs carrying contemporary avian or bovine H5N1 glycoproteins. At pasteurisation temperatures, viral infectivity was rapidly lost and became undetectable before the times recommended for pasteurisation. We then showed that an H5N1 HPAIV in milk was effectively inactivated by a comparable treatment, even though its genetic material remained detectable. We conclude that industry standard pasteurisation conditions should effectively inactivate H5N1 HPAIV in cows’ milk, but that unpasteurised milk could carry infectious influenza viruses.

RR:C19 Evidence Scale rating by reviewer:

  • Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.

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Review: In this preprint, all six virus strains, which included low and high pathogenicity avian viruses, were completely inactivated when subjected at 63 and 72C in less than 30 min and 15 seconds, respectively.

This research reports a series of experiments intended to investigate the inactivation of six different influenza virus by heating at temperatures typically used for pasteurization of milk, 63 and 72C. Individual virus strains were mixed with raw or commercially pasteurized milk and subjected to those temperatures. After different times, the residual number of active virus were determined. All experiments were very simple involving no more than three data points of measurement per experimental trial.

Overall, the results reported here supported the hypothesis that the temperatures used for commercial pasteurization inactivate influenza viruses, including a strain of HPAI. In all cases, there was no detection of active viruses after different sampling times between 10 to 1800 seconds at 63 C and between 5 and 15 seconds at 72 C.

From their results reported, Fig. 1e is irrelevant to the main hypothesis of this study and does very little to assess the viability of viruses in liquid media or milk. No information was provided on the experimental conditions and the time of sampling buffer and milk samples containing the viruses. In addition, the detection of viral nucleic acids as described in the manuscript is largely missing from the results.

This paper reaffirms the previous reports that pasteurization can eliminate the risk of exposure to HPAI from milk.