Inactivation of highly pathogenic avian influenza virus with high temperature short time continuous flow pasteurization and virus detection in bulk milk tanks

Authors: Spackman, Erica; ANDERSON, NATHAN - Us Food & Drug Administration (FDA); WALKER, STEPHEN - Us Food & Drug Administration (FDA); Suarez, David; Jones, Deana; MCCOIG, AMBER - Us Food & Drug Administration (FDA); COLONIUS, TRISTAN - Us Food & Drug Administration (FDA); RODDY, TIMOTHY - Us Food & Drug Administration (FDA); Chaplinski, Nick

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: With the recent discovery of bird flu virus infections in dairy cows and virus in milk there is a need to better understand how much virus can be in milk and to ensure that current milk processing methods are adequate to kill the virus. Therefore, 275 milk samples were collected from bulk storage tanks, which hold fresh milk before it goes to the processing plant. Samples were collected from counties where infected herds were known to be present. These milk samples were double blinded then were tested for virus genetic material by PCR methods. Positive samples (57.5%) were then tested for live virus. It was found that 14% of the total samples contained live virus at low levels, an average of about 3,000 infectious units per mL. To ensure that the standard heat treatment of milk used in the U.S. to kill bacteria, Pasteurization, will also kill bird flu we simulated commercial milk processing with a continuous flow pasteurizer. High levels of the bird flu virus (around 5 million infectious units) were added to fresh raw milk and was processed by standard times and temperatures, 161F for 15 seconds, then was tested for infectious virus. No live virus was recovered after numerous replicates. This showed that the standard treatment of milk in the U.S. is sufficient to eliminate at least 1,000 times as much virus that was found in the average positive bulk tank.

Technical Abstract: Infections of dairy cattle with clade 2.3.4.4b H5N1 highly pathogenic avian influenza virus (HPAIV) were reported in March 2024 in the U.S. and viable virus was detected at high levels in raw milk from infected cows. This study aimed to determine the potential quantities of infectious HPAIV in raw milk from affected farms and to confirm that the commonly used continuous flow pasteurization using the FDA approved 72°C for 15 s conditions for high temperature short time (HTST) processing, will inactivate the virus. Double-blinded raw milk samples from bulk storage tanks from affected farms (n=275) were collected in five states. Samples were screened for influenza A using quantitative real-time RT-PCR of which 158 (57.5%) were positive and were subsequently quantified in embryonating chicken eggs. Thirty-nine samples (14.2%) were positive for infectious virus with a mean of 3.5 log10 50% egg infectious doses (EID50) per mL. To closely simulate commercial milk pasteurization processing systems, a pilot-scale continuous flow pasteurizer was used to evaluate HPAIV inactivation in artificially contaminated raw milk using the minimum legal conditions in the US: 161°F (72°C) for 15s. Among all replicates at two flow rates (n=5 at 0.5L per min; n=4 at 1L per l min), no viable virus was detected. A mean reduction of =5.8 ± 0.2 log10 EID50 per mL occurred during the preheating phase where the milk is brought to 72.5°C before the pasteurization step. Therefore, standard U.S. continuous flow HTST milk pasteurization parameters consistently inactivated ~6 log10 EID50 per mL of HPAIV, which is ~3 log10 EID50 per mL greater than the average quantity of infectious virus detected in raw milk from bulk storage tank samples.