Fresh examinations show that milk from cows with influenza could cause illness in other creatures, posing queries about speedy pasteurization.
A team of scientists from the University of Wisconsin School of Veterinary Medicine are involved in a project called the Centers of Excellence for Influenza Research and Response (CEIRR), a federally funded programme conducting prompt research to address issues in the H5N1 outbreak in dairy cattle.
A paper published online on Friday in New England Journal of Medicine details the results of experiments with milk from four cows infected with the virus - two from New Mexico and two from Kansas. The research took place in a Biosafety Level 3 lab, adhering to strict safety regulations.
The team first verified that the raw milk was contaminated with the H5N1 virus, and then examined if levels of the virus would decrease over time when stored in a fridge. After five weeks, there was only a slight drop in viral levels in the raw milk.
Dr. Seema Lakdawala, an immunology and microbiology professor at Emory University and also part of the CEIRR network, but not involved in this study, commented on this finding, expressing concern that the virus was not decaying over time.
The researchers then tested various methods of pasteurization to determine which one inactivated the virus more effectively. Samples of milk were subjected to vat pasteurization, where it is heated at 63 degrees Celsius (145 degrees Fahrenheit) for intervals between 5 and 30 minutes, and flash pasteurization, conditions usually associated with high-temperature, short-time pasteurisation. This is the most common method employed in the US now.
Under the vat pasteurisation method, the milk samples were completely free of the virus. However, with the high-temperature short-time (flash pasteurisation) method, they observed a significant reduction in the level of the virus, but inactivation was not complete.
The researchers highlighted that the laboratory study did not fully replicate industrial-scale milk treatment.
Dr. Lakdawala advised against panicking over these findings, pointing out that industrial flash pasteurisation includes several steps, such as preheating and homogenisation, that increase the difficulty for the virus to survive. She emphasised the need for the complete process of commercial flash pasteurisation to be followed.
Between November 2021 and May 2022, tests conducted by the Food and Drug Administration (FDA) on 297 dairy products from retail stores returned evidence of H5N1 virus genetic material in roughly one-fifth of the milk sampled. These findings were reaffirmed after further testing, confirming that the viral fragments were inert and did not pose a threat to consumers. These tests were conducted as part of the FDA’s surveillance activities. The Centers for Disease Control (CDC) considers the risk to the general public to be low, advising against consumption of raw milk.
To date, there have been 58 dairy herds infected with H5N1 influenza in nine states. Michigan currently has the greatest number of infected herds, surpassing Texas.
To ascertain if the raw milk could infect other animals, the researchers gavaged some milk into mice. The mice fell sick the next day, with signs of illness including laboured breathing. The mice were euthanized on the fourth day, allowing the researchers to examine their bodies for the presence of the virus. They found the virus all over the mice's bodies, with high viral loads in their lungs and respiratory tract. The virus was also detected in the mice's mammary glands despite them not producing milk at the time. The team confirmed that raw milk can infect susceptible animals, which could indicate a risk to humans.
In an official statement, USDA officials denied knowing of any raw milk from infected farms being sold to consumers. However, not all dairy farms are testing their cows, and some infected cows in the current outbreak have shown no symptoms.
CDC Principal Deputy Director Dr. Nirav Shah asserted at a recent briefing that raw milk was dangerous, no matter the speed, and there were safer ways for individuals to protect themselves than consuming raw milk.
Interviewed about the new raw milk experiments, Kawaoka mentioned that the raw milk appeared to have more debris compared to typical milk. He assured that this would be removed before sale. Additionally, some of the milk appeared yellowish, but Kawaoka explained that milk from healthy and infected cows would be combined in large vats, making it appear normal and rendering it difficult to determine the safety of the milk just by appearance.
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The Centers for Disease Control (CDC) recommends avoiding consumption of raw milk due to its potential risk, given that it can infect susceptible animals as shown in the laboratory study. After five weeks, there was only a slight drop in viral levels of the H5N1 virus in the raw milk stored in a fridge, suggesting that the virus might not decay over time.
Source: edition.cnn.com
