Study reveals cows possess human flu receptors, increasing risk of bird flu transmission in milk-producing livestock.
"Their milk was noticeably thicker and had changed color, but it couldn't be attributed to the usual suspects like bacteria or tissue damage.
Several dairy farm owners called in, with one saying he believed his farm had the same mysterious virus, and half of his pets had died, hinting that the contagion had spread beyond just cattle.
Since it couldn't be explained by any known cause, Petersen sent samples from both sick and deceased animals to the Texas A&M state veterinary lab and to experts at Iowa State University.
What they discovered - an abundance of H5N1 influenza virus - has caused widespread alarm in the dairy industry and prompted public health officials around the world to vigilantly monitor the situation. It also increased the urgency of scientific research. One of the initial questions that needed to be answered was how the virus was infecting the cows to begin with.
Researchers in the US and Denmark took on this mission. Their preliminary study revealed that cows share the same receptors for flu viruses as both humans and birds. This raises the potential concern that cows could serve as intermediate hosts, aiding the virus in adapting to spread more effectively between people. While this scenario is uncommon, experts warn that it could lead to another pandemic.
For years, H5N1, or highly pathogenic avian influenza, has been primarily contained within the bird population. However, it has recently started to infect an increasing number of mammals, suggesting the virus might be evolving and inching closer towards becoming a human pathogen.
Avian flu viruses have ravaged commercial poultry operations in the US. Consequently, swines have been observed for any signs of infection. Cows, on the other hand, were not considered potential hosts.
Since late March, H5N1 has been detected in 42 infected herds across nine states in the US, reported the US Department of Agriculture. Only one individual has contracted H5N1 after coming into contact with infected cows. The US Centers for Disease Control and Prevention states that the current public health risk is low, and they're collaborating with several states to keep an eye on individuals with potential animal exposure.
"This finding in cattle has been quite different," said Dr. Lars Larsen, a professor of veterinary clinical microbiology at the University of Copenhagen in Denmark. Typically, flu viruses infect the lungs of mammals. In cats, it can also impact the brain. "Here, we see large amounts of virus in the mammary glands and the milk," Larsen said.
Larsen and his colleagues found that the concentration of H5N1 viruses in the milk of infected cows is one thousand times greater than what's usually observed in infected birds. They calculated that even if the milk from a single infected cow were mixed with 1,000 tons of milk, experts would still be able to detect traces of the virus in laboratory tests.
Tests conducted by the US Food and Drug Administration showed that about one-fifth of milk samples purchased from grocery stores contained inert fragments of H5N1 genetic material. This raised concerns over how widespread the virus had become. However, in later tests, it was confirmed that the pasteurized milk samples posed no threat to human health.
The outbreak has left many feeling uneasy. Milk and dairy products rank as the fourth largest agricultural commodity in terms of revenue in the US, according to the USDA's economic research service. Sales of cattle and calves rank as the second largest commodity.
How viruses enter cells
Viruses need a way to access healthy cells. The virus causing COVID-19 utilizes a receptor known as ACE2. For flu viruses, their entryway is a sugar molecule protruding from the surface of the cells called sialic acid.
Different animals have unique sialic acid receptors. Birds have sialic acid receptors in a specific shape that differ from those in the upper respiratory tracts of humans.
If you cross your index finger at a 90-degree angle, it represents the shape of a bird's sialic acid receptor. If you bend your index finger at the knuckle and create a curved shape, that's the shape of a human's sialic acid receptor. Flu viruses tend to favor one shape over the other, according to Dr. Andy Pekosz, a molecular microbiologist and immunologist at Johns Hopkins University.
Until recently, it was believed that cows didn't contract A-strain flu viruses like H5N1. But Larsen and his colleagues from the US and Denmark discovered that cows possess sialic acid receptors similar to those found in both humans and birds.
Researchers think this could be one explanation for why H5N1 hasn't efficiently spread between humans - it prefers attaching to one sialic acid receptor shape over the other."
-This is the paraphrased text.
The researchers were astonished by what they discovered: the alveoli, the teeny milk-producing pouches of the udder, were jam-packed with sialic acid receptors. Not only that, but these receptors had both the ones associated with birds and the ones more prevalent in humans. As per Dr. Charlotte Kristensen, a postdoctoral lecturer in veterinary pathology at the University of Copenhagen, every cell they examined had both types of receptors.
This revelation has generated significant concern as one method flu viruses undergo change and evolution is by exchanging portions of their genetic material with other flu viruses. This process, known as reassortment, necessitates that a cell is infected with two separate flu viruses at one time.
"If you get both viruses in the same cell at the same time, you can essentially get hybrid viruses emerging from it," said one of the study authors, Dr. Richard Webby, director of the World Health Organization Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds.
For a cow to be infected with both a bird flu virus and a human flu virus, it would need to possess both types of sialic acid receptors, which cattle do, an aspect that wasn't previously recognized.
"I think this is likely a relatively rare occurrence," commented Webby, who has spent the past 25 years researching the H5N1 virus.
For this to take place, a cow infested with the bird flu virus would need to acquire a different flu strain from an afflicted human. As human flu infections across the country are currently low and decreasing due to the conclusion of flu season, the likelihood of such an event happening is also diminished.
Although it's not a first, this phenomenon has happened before. Pigs also possess both human and bird sialic acid receptors in their respiratory tracts, and flu infections in pigs have been known to bring forth pandemic viruses. The 2009 pandemic triggered by the H1N1 influenza is thought to have initiated in pigs in Mexico when the virus reassorted to become one capable of rapid transmission among people.
Another way the bird flu virus could adapt in cattle, according to Webby, is a more gradual process and more common.
Each time a virus replicates itself, it makes errors. While some errors lessen the potency of the virus and limit its chances of survival, other times, these mistakes are fortuitous - at least for the virus. If a bird flu virus happened to mutate in such a way that it bound more easily to the human-type sialic acid receptors in cattle, this could bestow it with a survival advantage: the ability to infect more cells and various types of animals, like humans.
Viruses can skate and drift
Reassortment would represent a huge shift in the evolution of the virus, but the gradual passage of the virus through new hosts could also result in a change to the virus' genome through evolutionary drift.
In either case, it's distressing news, said Dr. Sam Scarpino, a computational biologist and director of AI and life sciences at Northeastern University.
"We now have a piece of data that suggests the risk profile is higher" Scarpino, who was not involved in the new study, stated.
He added that the findings are significant as no one had examined the susceptibility of cow tissues to influenza A viruses before.
"This is the first time I'm aware of. It doesn't mean there isn't another one out there, but a number of us scrutinized it meticulously and didn't find any," he said.
Kristensen noted that the researchers similarly couldn't locate any prior studies on this issue, hence their decision to conduct the research.
"We simply felt that, given the scenario, we should get these results out as fast as possible," Larsen added.
Additional experts stated that although there are numerous unknown variables to resolve, this study significantly raises the alert level.
"I think we now have enough evidence to conclude that what we need to do is to prevent transmission in dairy cattle," Scarpino said. "We need to increase the levels of protection that are enforced for workers who are in close contact with cows and milk products and elevate the funding dedicated to understanding influenza in cows because there's so much we don't know that we need to learn urgently."
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- The study by researchers in the US and Denmark revealed that cows share the same receptors for flu viruses as both humans and birds, which could potentially allow them to serve as intermediate hosts for the virus.
- The discovery of human-like sialic acid receptors in the milk-producing pouches of cows could increase the risk of viral reassortment, as it might enable the virus to bind more easily to human cells, potentially leading to a new strain capable of infecting people.
Source: edition.cnn.com
