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Review 1: "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 1: "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: This preprint shows that two different industry standard pasteurization treatments, both LTLT and HTST, effectively inactivates many different influenza A virus.  The high-temperature short-time treatment does inactivate H5N1, although it does not eliminate the ability to detect its DNA in a treated milk sample. These viruses remain viable in untreated raw milk.

Overall, the main conclusion of the study is supported by the data presented.  While I appreciate the point of this review is not to provide traditional line-item comments, there are a few important points about context and readability that I want to share for improving the work.

Saying pasteurization ‘temperatures’ alone inactivate viruses is insufficient. All thermal lethality is a combination of time and temperature. So the title could/should be revised somehow to reflect this.  The authors could maybe consider pasteurization ‘treatments’, which implies the industry standard time-temp combinations evaluated in the work.

The final concluding statement in the abstract, about the risk of unpasteurized milk, is supported by the paper but not supported by anything in the abstract. So if the abstract is read in isolation, it seems unsupported, and may be interpreted as some as an unreasonable attack on raw milk.  Which might lead some to dismiss the (very reasonable) point.

The main figure 1 has some challenges with readability.  It would help to provide short phrases next to the “abcd” letters, to tell briefly the point of the experiments.  Panel D is not interpretable in black and white, only in color. Since this is perhaps the most important direct finding in the paper, it would be useful to make it in a way that works in black and white.  Finally, it would help somewhere in the study to explain the seemingly arbitrary selection of sample times.  Like in panel A, why are there only points reporting when the data drop below the limit of detection (LOD), and for example not the 5 seconds data for samples that drop below LOD by 10 s. The authors should include the intermediate data.  And for panel C, presumably things were only tested at the end of LTLT 30 min or HTST 15 s and in this case, drawing lines between two points can be misleading (would LTLT inactivate before 30 min?).

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