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How Bird Flu Virus Fragments Get Into Milk Sold In Stores, And What The Spread Of H5N1 In Cows Means For The Dairy Industry And Milk Drinkers

The discovery of fragments of avian flu virus in milk sold in U.S. Stores, including in about 20% of samples in initial testing across the country, suggests that the H5N1 virus may be more widespread in dairy cattle than previously realized.

The Food and Drug Administration, which announced the early results from its nationally representative sampling on April 25, 2024, was quick to stress that it believes the commercial milk supply is safe. The FDA said initial tests did not detect any live, infectious virus. However, highly pathogenic avian influenza virus can make cows sick, and the flu virus's presence in herds in several states and new federal restrictions on the movement of dairy cows between states are putting economic pressure on farmers.

Five experts in infectious diseases in cattle from the University of California, Davis – Noelia Silva del Rio, Terry Lehenbauer, Richard Pereira, Robert Moeller and Todd Cornish – explain what the test results mean, how bird flu can spread to cattle and the impact on the industry.

What are viral fragments of avian flu, and can they pose risks to people?

It's crucial to understand that the presence of viral fragments of H5N1 doesn't indicate the presence of intact virus particles that could cause disease.

The commercial milk supply maintains safety through two critical measures:

First, milk sourced from sick animals is promptly diverted or disposed of, ensuring it does not enter the food chain.

Second, all milk at grocery stores is heat treated to reduce pathogen load to safe levels, mainly by pasteurization. Pasteurization has been shown to effectively inactivate H5N1 in eggs, and that process occurs at a lower temperature than is used for milk.

The viral fragments were detected using quantitative polymerase chain reaction testing, which is known for its exceptional sensitivity in detecting even trace amounts of viral genetic material. These fragments are only evidence that the virus was present in the milk. They aren't evidence that the virus is biologically active.

To evaluate whether the presence of the viral fragments corresponds to a virus with the capacity to replicate and cause disease, a different testing approach is necessary. Tests such as embryonated egg viability studies allow scientists to assess the virus's ability to replicate by injecting a sample into an embryonated chicken egg. That type of testing is underway.

On April 24, 2024, the FDA said it had found no reason to change its assessment that the U.S. Milk supply is safe. The agency does strongly advise against consuming raw milk and products derived from it because of its inherent risks of contamination with harmful pathogens, including avian flu viruses.

How does an avian flu virus get into cow's milk?

Currently, cows confirmed to have H5N1 have different symptoms than the typical flu-like symptoms observed in birds.

Abnormal milk and mastitis, an inflammatory response to infection, are common. While there is speculation that other bodily secretions, such as saliva, respiratory fluids, urine or feces, may also harbor the virus, that has yet to be confirmed.

How waterfowl or other birds transmitted H5N1 to cattle is still under investigation. In 2015, an outbreak of highly pathogenic avian influenza in commercial poultry farms reached its peak in April and May, the same time birds migrated north. Birds can shed the virus through their oral, nasal, urine and fecal secretions. So the virus could potentially be transmitted through direct contact, ingesting contaminated feed or water, or inhaling the virus.

Infected dairy cows can shed the virus in milk, and they likely can transmit it to other cows, but that still needs to be proven.

Contagious pathogens that cause mastitis can be transmitted through milking equipment or contaminated milker's gloves. Ongoing research will help determine whether this is also a potential transmission route for H5N1, and if so, what makes the virus thrive on mammary tissue.

If H5N1 is found to be widespread in milk, what risks can that pose for the dairy industry?

For the dairy industry, infection of cattle with H5N1 avian influenza virus creates challenges at two levels.

The overriding concern is always for the safety and healthfulness of milk and dairy products.

Existing state and federal regulations and industry practices require sick cows or cows with abnormal milk to be segregated so that their milk does not enter the food supply. Proper pasteurization should kill the virus so that it cannot cause infection.

The American Association of Bovine Practitioners has also developed biosecurity guidelines for H5N1, focusing on key practices. These include minimizing wild birds' contact with cattle and their environment, managing the movement of cattle between farms, isolating affected animals, avoiding feeding unpasteurized (raw) colostrum or milk to calves and other mammals, and ensuring the use of protective personal equipment for animal caretakers.

The other major concern is for the health of the dairy herd and the people who take care of the dairy cattle. A farm worker who handled dairy cows contracted H5N1 in Texas in March 2024, but such cases are rare.

No vaccines or specific therapies are available for avian influenza infections in dairy cattle. But following good sanitation and biosecurity practices for both people and cows will help to reduce risk of exposure and spread of the avian influenza virus among dairy cattle.

For cows that get the virus, providing supportive care, including fluids and fever reducers as needed, can help them get through the illness, which can also cause loss of appetite and affect their milk production.

Dairy farms facing an outbreak will have economic losses from caring for sick animals and the temporary reduction in milk sales. Approximately 5% to 20% of the animals in the affected herds have become ill, according to early estimates. Affected animals typically recover within 10 to 20 days.

At least 22 states have restricted importing dairy cattle to prevent the virus's spread, and the federal government announced it will require that lactating dairy cattle be tested before they can be moved between states starting April 29, 2024. While the overall impact on U.S. Milk production is projected to be minor on an annual basis, it could lead to short-lived supply disruptions.

How worried should people be about avian flu?

The federal government's monitoring and food safety measures, along with pasteurization, provide important safeguards to protect the public from potential exposure to avian influenza virus through the food chain.

Drinking raw milk, however, does represent a risk for exposure to multiple diseases, including H5N1. This is why the FDA and Centers for Disease Control and Prevention strongly recommend drinking only pasteurized milk and dairy products.

This article, published April 25, 2024, has been updated with new FDA test results.

This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Noelia Silva del Rio, University of California, Davis; Richard V. Pereira, University of California, Davis; Robert B. Moeller, University of California, Davis; Terry W. Lehenbauer, A person in Texas caught bird flu after mixing with dairy cattle. Should we be worried?

How deforestation helps deadly viruses jump from animals to humansNew Jersey's small, networked dairy farms are a model for a more resilient food system

Noelia Silva del Rio has received funding from CDFA and USDA-NIFA

Richard V. Pereira has received funding from CDFA and USDA-NIFA.

Robert B. Moeller, Terry W. Lehenbauer, and Todd Cornish do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.

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FDA Finds Traces Of Bird Flu Virus In Grocery Store Milk But Says Pasteurized Dairy Is Still Safe

The next pandemic could strike crops, not people The next pandemic could strike crops, not people

Nobody really knows how the fungus Bipolaris maydis got into the cornfields of the United States. But by the summer of 1970, it was there with a vengeance, inflicting a disease called southern corn leaf blight, which causes stalks to wither and die. The South got hit first, then the disease spread through Tennessee and Kentucky before heading up into Illinois, Missouri, and Iowa — the heart of the Corn Belt.

The destruction was unprecedented. All told, the corn harvest of 1970 was reduced by about 15 percent. Collectively, farmers lost almost 700 million bushels of corn that could have fed livestock and humans, at an economic cost of a billion dollars. More calories were lost than during Ireland's Great Famine in the 1840s, when disease decimated potato fields.

Really, the problem with southern corn leaf blight started years before the 1970 outbreak, when scientists in the 1930s developed a strain of corn with a genetic quirk that made it a breeze for seed companies to crank out. Farmers liked the strain's high yields. By the 1970s, that particular variety formed the genetic basis for up to 90 percent of the corn grown around the country, compared to the thousands of varieties farmers had grown previously.  

That particular strain of corn — known as cms-T — proved highly susceptible to southern corn leaf blight. So, when an unusually warm, wet spring favored the fungus, it had an overabundance of corn plants to burn through.

At the time, scientists hoped a lesson had been learned. 

"Never again should a major cultivated species be molded into such uniformity that it is so universally vulnerable to attack by a pathogen," wrote plant pathologist Arnold John Ullstrup in a review of the matter published in 1972.

And yet, today, genetic uniformity is one of the main features of most large-scale agricultural systems, leading some scientists to warn that conditions are ripe for more major outbreaks of plant disease. 

"I think we have all the conditions for a pandemic in agricultural systems to occur," said agricologist Miguel Altieri, a professor emeritus from the University of California, Berkeley. Hunger and economic hardship would likely ensue.

Climate change adds to the danger — shifting weather patterns are on track to shake up the distributions of pathogens and bring them into contact with new plant species, potentially making crop disease much worse, said Brajesh Singh, an expert in soil science at Western Sydney University in Australia. 

Incorporating biodiversity into large-scale farming could move agriculture away from this crisis. Here and there, some farmers are taking steps in this direction. But will their efforts become widespread — and what will happen if they don't? 

Grist goes deep on the history of genetic manipulation of crops and how it might lead to a dire threat to the world's food supply.

Sepia Times / Universal Images Group via Getty Images Industrialization made food a global commodity, the burdens of which made crop diversification difficult

Farms cover close to 40 percent of the planet's land, according to a 2019 report from the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. Almost 50 percent of those systems are made up of just four crops: wheat, corn, rice, and soybeans. Disease is commonplace — globally, $30 billion worth of food is lost to pathogens every year.

Things were not always this way. As the 1900s dawned in the United States, for instance, food was produced by humans, not machines — more than 40 percent of the American workforce was employed on a multitude of small farms growing a wide range of crop varieties. The British Empire sparked the shift toward today's industrialized food system, said historian Lizzie Collingham, who wrote the book "Taste of War: World War II and the Battle for Food."

By the early 1900s, the British Empire had learned that it could "basically treat the whole planet as a resource for its population," Collingham said. It acquired cocoa from West Africa, meat from Argentina, and sugar from the Caribbean, for example. Suddenly, food was not something to be bought from the farmer down the street, but a global commodity, subject to economies of scale.

America grabbed hold of this idea and ran with it, according to Collingham. First came the New Deal — President Roosevelt's plan for pulling the country out of the Great Depression included raising the standard of living for farmers, partly by bringing electricity to rural life. In 1933, farm country was characterized by outhouses, iceboxes, and a complete lack of street lights. By 1945, all that had changed.

Once they were on the power grid, farmers could buy equipment such as electric milk coolers and feed grinders that let them scale up their operations, but such things are expensive — only by expanding could farmers afford them. "It all makes sense if you rationalize it for economies of scale and make your farm into a factory," Collingham said.

Then World War II hit, and much of agriculture's workforce had to go off to fight. At the same time, the government had an army to feed and the general public to keep happy, so it really needed to keep the food supply coming. Machines were the answer — the war era solidified the shift from humans to tractors. And machines do best when they only perform one job, like harvesting a single crop, acre after acre.

Monocultures can be very efficient when they're not contracting diseases, and that efficiency is part of what got the United States through the war. In fact, the system worked so well that "soldiers doing their training in America got fatter," Collingham said. "A lot of them had never eaten so well in their lives."

Soon, small-scale farms growing diverse crops had largely retreated into the past in the Midwestern U.S. It's not that anyone intended for the practice to be lost. It was simply "in many people's minds, rendered obsolete," said agronomist Matt Liebman, who recently retired from Iowa State University. 

maerzkind/Getty Images Not all microbes are bad, and limiting or eliminating them can negatively impact biodiversity

One might think the realization that biodiversity protects plant health is a new one, given that it wasn't that long ago that biodiverse farming became a rare practice. But in fact, scientists and farmers have recognized this connection for at least centuries, and probably longer, said evolutionary biologist Amanda Gibson from the University of Virginia.

The basic concept is simple enough: A typical pathogen can only infect certain plant species. When that pathogen ends up on a species it can't infect, that plant acts like a sinkhole. The pathogen can't reproduce, so it's neutralized, and nearby plants are spared.

Disease-resistant plants can also alter airflow in ways that keep plants dry and healthy and create physical barriers that block pathogen movement. Especially if they're tall, resistant plants can act like fences that diseases have to hop over. "Somebody did a nice experiment taking dead corn stalks and just plopping them in the bean field," said plant pathologist Gregory Gilbert from the University of California, Santa Cruz. "And that works, too, because it's just keeping things from moving around."

In nature, this dynamic between plants and pathogens can be part of healthy ecosystems. Pathogens spread easily between stands of the same species, killing off plants that are too close to their relatives and making sure landscapes have a healthy degree of biodiversity. As "social distancing" is restored between susceptible hosts, the disease dies down.

In monocultures, there are no sinkholes or natural fences to stem the spread of pathogens. Instead, when a disease takes hold in a crop field, it's poised to burn through the entire thing. "We create amplification rather than dilution," said Altieri.

New technology has driven home these old lessons: Over the last decade, it's become possible for scientists to isolate a broad swath of the microbes found within a particular niche — like an ear of corn or a stalk of wheat — and use DNA sequencing to create a censuslike list of everything that lives there.

The results have been unsettling, but not always unexpected. Plants in cultivated lands carry a significantly larger variety of viruses than those in adjacent biodiversity hotspots, plant and microbial ecologist Carolyn Malmstrom from Michigan State University and her colleagues found in one study. 

Conversely, they later found that some fields of barley and wheat were largely devoid of viruses, but that could also be a sign of problems to come. Pesticides may be keeping virus levels low: "So we might think, OK, yay, we're protecting our crops," Malmstrom said. But not all microbes are bad. 

"By pulling our crop systems out into a virus-free situation, we may also be removing them from some of the richness of the biodiversity of microbes that's beneficial," she added.

The bigger the farm, the more serious the disease problems, at least in the case of a pathogen called Potato virus Y, which leads to low potato yields. When researchers looked at the amount of simplified cropland surrounding a potato plant, they found that the prevalence of the pathogen went up steadily as the percentage of surrounding area covered in cropland increased. Unmanaged fields and forests, on the other hand — carrying wild mixes of plants — seemed to have a protective effect.

In natural landscapes, increasing biodiversity lowers the number of virus species present. But increasing biodiversity along the edges of crop fields doesn't seem to have the same effect, plant ecologist Hanna Susi from the University of Helsinki found. 

Fertilizers and other chemicals leached from the crops might affect the susceptibility of nearby plants to infection, Susi and her coauthor postulated. Beneficial microbes found on wild plants may be keeping many of these viruses from causing disease, but if the same viruses get into crops that lack that protection, "We don't know what may happen," she said. Farmers could find themselves dealing with new kinds of crop diseases.

On Altieri's farm in the Colombian state of Antioquia, he mixes many plants — corn with squash, pineapples with legumes — and said, "We don't have the diseases that neighbors have, that have monocultures." 

The results of recent DNA-sequencing experiments are familiar to him because traditional Latin American farmers have long used biodiversity to protect their crops. "These papers are good ecological research," he said. "But actually, they're basically reinventing the wheel."

This old wheel does have to get over a new hill, however. Climate change is redistributing pathogens, bringing them into contact with new crops, and changing weather patterns in ways that foster disease.

Already, Liebman has seen the effects of climate change firsthand in Iowa, where tar spot disease — an infection that kills the leaves on corn plants — is on the rise. "We have warmer nights and more humid days," he said. The tar spot pathogen loves the new weather.

Predicting exactly how much climate change will increase crop disease is difficult, said Singh. But there are some general conclusions he can draw.

Rising temperatures will likely favor certain pathogens that cause disease in major crops. A wheat-infecting fungus called Fusarium culmorum, for example, is likely to be replaced by its more aggressive and heat-tolerant relative, Fusarium graminearum. That could spell bad news for Nordic countries, where wheat crops could suffer.

Hotter temperatures will likely knock back other pathogens. A fungus that infects the herb meadowsweet, for example, has already begun dying out on islands off the coast of Sweden. In general, however, Singh thinks regions that are currently cold or temperate will likely see increases in crop disease as they warm.

For regions that are already warm, rising humidity could cause trouble. For example, parts of Africa and South America are among the regions that will probably see increases in funguslike pathogens called Phytophthora. Food insecurity is already prevalent in some of these areas, and if nothing's done to stop disease spread, that's likely to get worse. "We need a lot more information," Singh said. "But I agree that that is one of the scenarios that is a possibility." 

Ben Hasty / MediaNews Group / Reading Eagle via Getty Images Intercropping may provide a means of making large-scale agriculture more biodiverse

Photo: Intercropping with rows of corn planted alongside coffee at a farm in Brazil.

Jason Mauck farms "every which way," in his words. The head of Constant Canopy Farm likes experimenting, seeing what works and what doesn't. And on about 100 out of the 3,000 acres he tends to in Gaston, Indiana, one of his experiments involves a strategy called intercropping.

Intercropping means growing two or more crops in the same field, by alternating rows or mixing the crops within the same rows — it's a modern reimagining of age-old techniques like those Altieri uses, and one way of introducing biodiversity into large-scale agriculture. In Mauck's case, he's planting wheat with soybeans. The wheat seeds go into the ground in October, and by February, the plants are poking up through the soil. Then in April, he adds soybeans between the rows. The two crops grow together until the harvest, right around July 1.

Unlike the wheat Mauck grows in a monoculture, he doesn't spray the intercropped wheat with fungicides at all — they simply don't need the help to stay healthy. The combination of crops likely encourages airflow that dries moisture and prevents fungus from growing, Mauck said. With climate change bringing more extreme storms to the region, he welcomes the help. 

Mauck's experiences are far from unique. When biologist Mark Boudreau from Penn State Brandywine reviewed 206 studies on intercropping across a wide variety of plants and pathogens, he found that disease was reduced in 73 percent of the studies.

In China, farmers have been experimenting with intercropping for decades, and it's catching on in Europe and the Middle East, Boudreau said. But in the American Midwest, Mauck said intercropping makes him "kind of a weirdo." He speaks at about 20 conventions every year to spread the word about this and other sustainable farming practices, plus he has a lively social media following. He's convinced some of his fellow farmers to try intercropping, but progress is slow.

Lack of equipment is a big part of the problem, said extension agronomist Clair Keene from North Dakota State University. Farm equipment companies haven't invented the machine that will let farmers harvest mixed crops separately, and farmers usually don't have the time to do multiple harvests. That would be an easy enough problem for farm equipment companies to solve, Boudreau thinks, if farmers put a bit of pressure on them.

In North Dakota, the humble chickpea might just provide the motivation farmers and farm equipment companies need. In recent years, the profit margin on chickpeas has been two to three times that of spring wheat — a common crop for the region. But there's a problem: Chickpeas are very susceptible to a disease called Ascochyta leaf blight. "It can just wipe out the field. Like, there will be no chickpeas left to harvest," Keene said. To avoid this fate, farmers spray their chickpeas with fungicides between two and five times a year, and the cost of the fungicides really cuts into the profit margin.

Intercropping could be an affordable alternative. Keene and others have found that Ascochyta leaf blight drops by at least 50 percent when chickpeas are grown along with flax. Like in Mauck's fields, Keene thinks flax promotes airflow around the chickpeas, reducing moisture and preventing the blight-causing fungus from growing.

When Keene looks across the expansive crop fields that characterize her home state of North Dakota, she sees two sides to modern agriculture. On the one hand, monocultures have given many people a vital source of calories. "We as Americans — we're using our landscape to provide a quality of life that, at least writ large, wasn't ever dreamed of by generations before us," she said. "And who's making that happen? Farmers. We owe them a lot."

But the same agricultural system has impacted the landscape dramatically, from the native plants that used to thrive in Midwestern prairies to the microbes that populate the soil. Changes are brewing in Earth's climate, and a system we've come to rely on may start to falter. Modern agriculture has offered humans comfort: "But," Keene asked, "at what ecological cost?"

 

This story was produced by Grist and reviewed and distributed by Stacker Media.

Lena Trindade / Brazil Photos / LightRocket via Getty Images

High Risk Of Animal-to-human Diseases Developing In Some China Fur Farms, Animal Protection Group Says

HONG KONG (Reuters) - An investigation of five fur farms in China housing foxes, raccoon dogs and mink found a high risk of diseases developing that could jump from animals to humans, said animal protection group Humane Society International who conducted the study at the end of 2023.

The farms in China's northern Hebei and Liaoning provinces each held between 2,000 and 4,000 animals in intensive conditions, including in close proximity to poultry, HSI said.

Alastair MacMillan, a visiting professor at Surrey University's Veterinary School, said the high stocking density of the animals facilitates the rapid spread of viruses on droplets from one to another, and potentially to humans.

"The rapid circulation and mixing of different strains of virus from animal to animal facilitates their adaption to a mammalian host, the development of mutant strains of concern and a greater likelihood of a threat of human infection."

China's Ministry of Agriculture and Rural Affairs did not respond to requests for comment regarding the conditions on the fur farms and the risk of disease spread.

MacMillan said that from a disease transmission and public health perspective the footage was extremely worrying as it is well known that animals farmed for their fur are susceptible to respiratory viruses that can infect humans.

Data from the early days of the COVID-19 pandemic briefly uploaded to a database by Chinese scientists last year suggested raccoon dogs may also have been involved in coronavirus reaching humans.

Photos and footage from HSI showed animals densely packed in small empty cages with wire mesh floors. Reuters was not able to independently verify the footage.

Many animals could be seen pacing up and down repetitively, an action linked to psychological distress, according to veterinary experts.

"Mentally disturbed animals, piles of animal filth, barren cages and worrying zoonotic disease is in stark contrast to the glamorous image the fur trade tries to portray," said Peter Li, HSI's China policy expert.

Even as China's fur production has fallen in line with global trends, down 50% from 2022 to 2023 and a near 90% decline in the past decade, there appears to be still robust demand for fur.

Social media platforms such as e-commerce site Xiaohongshu and Weibo showed users discussing wearing fur as desirable and practical for keeping warm.

(Reporting by Farah Master; additional reporting by Edward Cho; Editing by Hugh Lawson)

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