There are concerns about the spread of bird flu among cows and the detection of virus fragments in milk sold in US grocery stores. People are worried about the virus's potential to infect mammals, and whether drinking the contaminated milk can transmit bird flu to humans.
Science News approached experts for answers. In short, the risk to people is low due to milk pasteurization and the way bird flu spreads.
Are there bird flu viruses in cow milk?
It's unlikely in pasteurized milk.
On April 23, the FDA revealed that genetic material of bird flu was found in grocery store milk. About 1 in 5 samples contained virus RNA, with a higher likelihood in areas with infected dairy cows. Is it possible for whole infectious viruses to be present in the milk?According to Michael Osterholm, from the University of Minnesota, the pasteurization process effectively kills the virus particles, so there is no need to worry about ingesting infectious material.
Osterholm believes that the presence of genetic remains of the flu virus does not automatically indicate a public health concern.
The pasteurization process eliminates bacteria and viruses by heating milk to high temperatures. As Osterholm explains, fragments of dead bacteria have always been present in milk. Therefore, finding genetic remnants of the flu virus is not a cause for public health concern.
H5N1 is an envelope virus, which is easier to inactivate than non-envelope viruses, says Meghan Davis, an environmental epidemiologist at Johns Hopkins Bloomberg School of Public Health. E. coli and Listeria The FDA stated on April 23 that studies have not directly tested milk pasteurization's ability to kill the H5N1 virus, but pasteurization of egg has been shown to inactivate the virus, which provides reassurance about the effectiveness of pasteurization.
Government officials emphasize that pasteurized milk is safe to drink, but advise against consuming raw milk, which has not undergone pasteurization.
Due to the potential risk of other infectious diseases, Davis does not recommend consuming raw milk and products made from it. Davis recommends avoiding raw goat and sheep milk products as some goats have also been infected with H5N1..
Is it possible for people to get bird flu from eating or drinking?
Osterholm says that evidence from decades suggests it’s unlikely that humans have been infected with influenza A virus through ingestion.
Some scavenger mammals have been infected with H5N1 from eating dead birds. However, influenza viruses need to attach to certain sugars on cell surface proteins to enter cells. These sugars are different in humans compared to scavengers. The one case of human infection from bird flu in the United States occurred in a person who worked with cows and had an eye infection called conjunctivitis.
Osterholm says it may be challenging for people to catch bird flu from infected cows. The experience in recent years has shown very few infections in humans despite significant contact with infected flocks of turkeys and chickens. The U.S. Centers for Disease Control and Prevention and World Health Organization consider the virus to be low risk for humans.
Where is bird flu spreading in the United States at the moment?
The U.S. Department of Agriculture initially reported the discovery of a strain of bird flu in dairy cattle.
bird flu has been found in dairy cows in Kansas and Texas on March 25.
Since then, the virus has been found in dairy cows in eight states, and the same strain has also been found in poultry in five states. Following this, the USDA issued a federal order requiring mandatory testing of dairy cows before they can be moved to another state, as well as tracing their previous movements from infected herds.
The virus has also been found in poultry in five states. The USDA's order mandates mandatory testing for all dairy cows before they can be transported to another state, and requires tracking the previous movements of cows from infected herds. This order will take effect on April 29. The particular strain of bird flu, clade 2.3.4.4b, has been found in poultry in five states. The particular strain of bird flu, clade 2.3.4.4b, has been found in poultry in five states. The USDA's order mandates mandatory testing for all dairy cows before they can be transported to another state, and requires tracking the previous movements of cows from infected herds. This order will take effect on April 29.SN: 4/3/24The virus may have only jumped into cattle once and then spread from cow to cow, according to evolutionary biologist Michael Worobey of the University of Arizona in Tucson. In late December 2023, evolutionary biologist Michael Worobey of the University of Arizona in Tucson suggested that the virus may have jumped into cattle only once and then spread from cow to cow, a few months earlier than previously believed. Where did the bird flu virus spread in late December 2023?
H5N1 According to evolutionary biologist Michael Worobey of the University of Arizona in Tucson, the virus may have jumped into cattle only once and then spread from cow to cow in late December 2023, which is earlier than previously thought. The findings, posted by evolutionary biologist Michael Worobey of the University of Arizona in Tucson, are preliminary and have not been independently verified by other scientists, according to Davis. However, they suggest that bird flu in cattle may be more widespread than reported cases on the USDA dashboard. It is potentially circulating from cow to cow, but the full extent is not yet known. Davis states that there is both concern and reassurance at the moment. Despite the low risk, the H5N1 virus has been globally present since 2020 and it has been in the U.S. since 2022. The virus continues to cause major outbreaks in birds and has spread to many species of mammals, which differs from earlier iterations of H5N1 avian influenza that would flare up and then die off the next year.Can cows get infected with bird flu?
Yes, but usually the cases are not very severe. H5N1 infections in cows can lead to a decrease in appetite and milk production
as well as irregular feces, fatigue, fever, and other symptoms
.
Davis, a former dairy vet, mentions that vets often receive reports of cows being “off feed,” meaning they are not eating well or producing as much milk as usual. These symptoms are not unique to any specific disease, so cases of H5N1 flu might have been missed. Some cows may show no symptoms. Lung tissue from one asymptomatic cow tested positive for the virus, as per the USDA announcement on April 24.The virus has also been detected in
cats at dairy farms in Texas
and in Poland, South Korea, and France. According to the World Organization for Animal Health, at least one cat has died.
For poultry like chickens and turkeys, the virus can be lethal, wiping out flocks in a few days. Can H5N1 evolve to infect people more easily? It's possible, Osterholm states. “In our line of work, we are always vigilant because the virus could potentially change through mutation or reassortment at any time.”
Reassortment occurs when flu strains swap some of their genetic instructions. The H1N1 flu strain that caused the 2009 pandemic was generated through reassortment. In a pig, fragments from the
1918 pandemic flu strain combined with
portions from a virus that was already a mix of
a swine flu virus and an avian flu virus . The resulting virus eventually infected people ( SN: 5/22/09; SN: 2/12/10 ). The current H5N1 resulted from thereassortment of avian flu virusesfrom poultry and wild birds.“Our concern is the virus adapting to better match some of the receptors found in humans, which is why any transmission from bird populations to mammals is a cause for worry,” says Davis. Those working on dairy farms, individuals in the dairy production chain, and anyone else who may come into contact with raw milk, cows, or poultry should wear protective gear to avoid potential infection. Davis also suggests testing farm workers, their families, and others in their communities. Both Davis and Osterholm are worried about the virus spreading to other food animals. “The challenge I currently see on U.S. farms is a virus making its way into hogs,” Osterholm remarks. Pigs have receptors similar to those found in both humans and birds, making them an ideal host for bird flus that have the potential to cause a pandemic. Meanwhile, Davis states, “if this virus can infect both cows and goats, sheep are on my list of suspected species of concern.”
H5N1 avian flu viruses have been present in birds since 1996 and have affected
over 880 people
globally since 1997. In the United States, a
poultry worker tested positive for H5N1 in 2022. The dairy farmworker with conjunctivitis was only the second documented case of bird flu infection in the United States. So far, H5N1 has not acquired the ability to easily spread from person to person, which would make it a potential pandemic virus. “Anything could happen at any moment,” says Osterholm, “but based on the current record, there is very little evidence to support the idea that this virus will infect humans and then be transmitted from person to person.” We inquired of the specialists: Is it necessary for people to be concerned? The method of pasteurization and the way the H5N1 virus infects indicates that the risk to people is still minimal. tested positive for H5N1 in 2022. The dairy farmworker with conjunctivitis was only the second person in the United States with a documented bird flu infection.
So far, H5N1 has not developed the ability to spread easily from person-to-person, which would make it a pandemic-potential virus. “Lightning could strike tomorrow,” Osterholm says, “but at least based on the track record so far, there’s been very little evidence to support that this is going to infect humans [and] then be transmitted by people to other people.”
