Iowa State University study shows it’s possible for bird flu to infect mammary glands

Iowa has seen low-level transmission of bird flu across the state this year, but researchers at Iowa State University are sounding the alarm about a possible new way the virus could spread.

The study by Iowa State University researchers, published last month in the Journal of Dairy Science, found that the mammary glands of mammals can be infected with H5N1 bird flu.

The ISU research team found that the mammary glands of pigs, sheep, goats, beef cattle, alpacas and even humans, are “biologically suitable” to be infected by and host the virus.

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Rahul Nelli, the study’s lead author and a research assistant professor of veterinary diagnostic and production animal medicine at ISU, said mammals’ mammary glands have the potential to harbor the virus because the glands have high levels of sialic acids, sugar molecules in the body that are crucial for milk production.

“The main thing we wanted to understand in this study is whether there is potential for transmission among these other domestic mammals and humans, and it looks like there is,” Nelli said.

H5N1, or bird flu, has affected more than 30 million birds in Iowa since the current outbreak began in February 2022.

The research, which was done in partnership with the National Animal Disease Center, began after the detection in March 2024 of avian flu in dairy cattle, which led to contaminated milk.

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Only a handful of H5N1 cases have been reported in mammals, but Todd Bell, professor of veterinary pathology at ISU and a study co-author, said other domestic animals that may be in contact with wild birds aren't being tested on a widespread and consistent basis.

“If we don’t look, we don’t know,” he said.

Bell said the initial detections of avian flu in dairy cattle were from “spillover” events from wild birds, and the team wanted to find out if other animals on mixed animal farms also could be infected. He said the goal of the research was to determine if a bird that tested positive for the virus could spread it to other animals in the food chain. Researchers found it is possible.

As avian influenza evolves, the researchers will be expanding their research beyond looking at mammary glands.

“In the future studies, we are actually adding more other tissues because the virus we have, as we are seeing, is evolving. Influenza is traditionally replicated in the respiratory tract, but we are seeing virus RNA being detected in urine, in uterus samples. It's detected in samples like the rumen as well,” Nelli said, referring to a stomach compartment in animals like cows, sheep and goats. “There's a lot going on, so we don't know what's happening systemwide.”

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Mitigating risks

Although avian influenza is circulating, Nelli said it’s not an immediate threat.

However, he said “we need to be cautious about the approaches we take,” including not drinking raw milk.

It’s “as simple as that,” Nelli said, adding that pasteurized dairy products are widely available. It can “reduce the chances of any kind of potential for infections in these animals and through them, humans getting cross-contamination through any of these products.”

Nelli said the point of contact for influenza in humans is through the respiratory tract, but if the virus binds and replicates, it could become possible for a mother to pass it to a child through breast milk.

He cautioned that it’s still unknown how much the virus would be able to replicate and spread through breastfeeding, and his team and others are continuing their research.

“We don't want to be alarmist, but at the same time, we have these receptors there, so we just want all the research community to be aware of this,” Nelli said. “Let's start looking into this more closely and see what can be addressed and how we can mitigate this virus before it's spreading as a large-scale outbreak.”

Bell agreed, adding that the risk to the public is low.

“But that being said, we need to continue to be vigilant and looking for this at all times, and making sure it is not changing, making sure it's not showing up in spots that we didn't anticipate or think it was going to show up before,” Bell said. “Because I can tell you for certain, nobody expected this to show up in the milk of dairy cows.”

To keep the risk low among humans, the researchers said that use of PPE — personal protective equipment — by producers is key.

Nelli said PPE, including masks, gloves and eye gear, is helpful in reducing the spread of the virus. Farms also should use disinfects and thoroughly clean areas where animals are kept. Strong biosecurity measures are important, he said.

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Bell said the researchers’ goal is to come back with additional studies that help answer some of the outstanding questions raised in their first study, like whether other animals can be infected and how they can be infected.

He pointed to the guidance laid out by the U.S. Department of Agriculture as a solid information source for Iowans looking to protect their farming operations or learn more about the virus.

“I'm hopeful and optimistic that maybe some of our research has helped them with some of those recommendations, specifically mixed species, making sure that different types of species have different segments (of land), they have different water and food, so that's not mixing together,” Bell said. “We don't know for sure if our research is up with that, but we would like to think that some of that research that we're doing is going to help them make those kinds of decisions, that they're going to make those farms more bio-secure.”

Bird flu levels across Iowa

Iowa has been “pretty fortunate” with low levels of bird flu detected in the state this fall, according to Yuko Sato, poultry extension veterinarian and diagnostic pathologist at the Veterinary Diagnostic Lab at Iowa State University.

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The state reported a positive case in Calhoun County in October and in another in early December in Hamilton County, but Iowa has had “a little bit of a lull period compared our neighbors to the east and west,” Sato said.

That doesn’t mean testing isn’t happening. Sato said the Veterinary Diagnostic Lab at ISU tests for the virus at high levels. She described two types of testing: active surveillance and passive surveillance.

Active surveillance involves testing on a routine basis to make sure influenza doesn’t pop up, or to act as soon as it does.

Sato said producers will actively test by sending PCR swab tests to laboratories for testing, similar to COVID-19 tests, on a routine basis. She said this happens “24/7” on commercial farms.

Passive surveillance happens when a bird is already sick with what could be avian influenza.

“When producers get a trigger like mortality suddenly jumped or don’t have a good reason why birds are dying, that's when they'll send in samples to make sure that they're not dealing with something terrible,” Sato said. “The key is to have early detection so we can control the outbreak, so it doesn't spread.”

The most recent detection of the virus seen in Iowa was on Dec. 18, according to the Iowa DNR, after Canada geese tested positive for avian influenza at Green Valley Lake and the Lake of Three Fires in southwest Iowa.

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An ongoing threat

Bell said influenza is a “crafty” virus that can mutate and create new strains.

He described influenza viruses meeting in a single cell as “playing cards” with their gene segments.

“If you get two separate viruses, like the seasonal human viruses, like H1N1 and H3N2 infects a cell, and then you have, for example, this high path virus infects that same cell,” Bell said, “not only do these viruses tend to not proofread well and have mutations, but they also have segments. They have eight different gene segments each one of them, and what happens when those two viruses affect the same cell?”

Bell said many human pandemics throughout history have started when influenza-infected cells swapped these “cards.” “Here you have influenza viruses from different species, mixing in the same species, be that a human, be that a pig, be that a bird, but these two different viruses go in, and a new one can pop out at the end.”

“Because of this playing card scenario where they can swap segments, these new viruses pop out, and those new viruses then have not been seen by either the animal or human population,” he said.

Consequently, neither humans nor animals have immunologic memories of the infection, delaying the body’s immune response to infection.

“That's why we get the flu vaccines, so your body has seen it before and can react when challenged. But if your body does not have that immunologic memory to this new virus, because it's got these different playing cards, it could potentially do a lot of damage before you can either get a vaccine or get antivirals developed, or kind of put other biosecurity measures in place against that virus,” Bell said. “It's very crafty.”

Olivia Cohen covers energy and environment for The Gazette and is a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

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Comments: olivia.cohen@thegazette.com