Infectious Disease Experts Warn Bird Flu Outbreak Bigger Than Previously Thought

For weeks, the dairy industry has been gripped by a highly contagious virus that is threatening to only get worse. Federal regulators announced this week that samples of pasteurized milk tested positive for H5N1, the strain of bird flu that has jumped from poultry to cows with one recent infection in an American.

At the moment, the U.S. Food and Drug Administration (FDA) reports that the country’s milk supply is safe thanks to the pasteurization process, which works by heating milk to kill bacteria and viruses, and “the diversion or destruction of milk from sick cows.”

However, infectious disease experts warn that these positive tests are a sign that the outbreak is much bigger than previously thought, and indicate that the government doesn’t have a good grasp on the situation. And the problem only seems to be worsening. According to the USDA’s Animal and Plant Health Inspection Service (APHIS), H5N1 has been identified in 33 herds in eight states. On Thursday, a senior FDA official said 1 in 5 milk samples have tested positive for H5N1.

While experts aren’t expecting a H5N1 pandemic in humans to spread across the United States this year, yet, it’s likely it could be the next pandemic in the not-so-distant future. The fact that the current spread between species, and even to a few humans, is likely underestimated could mean that an emergency could arrive too late to contain.

Katelyn Jetelina, an epidemiologist and author of the newsletter Your Local Epidemiologist, told Salon “the worst case scenario” is that this turns into a “massive pandemic.” If a person asked a group of epidemiologists what the next pandemic is going to be, a majority would likely say “bird flu,” she said.

“I think what would be most helpful is to mount a proactive response rather than always being in this reactive, defensive mode with diseases,” Jetelina said. “And if we can understand where it’s going, how it’s changing, then we can certainly prepare and know when it jumps to humans and when we do need to employ all the other steps.”

Such steps include making more vaccines, starting to get frontline workers vaccinated and more.

“But if we’re not following it, this could easily jump and start spreading without us knowing for a while,” Jetelina said. “And by then we’re already in this reactive-defensive perspective.”

Just like humans, birds can get the flu. When that happens, they can pass it on to other poultry — such as chickens, ducks and turkeys. But the most recent strain of avian influenza, H5N1, has jumped species. Instead of only infecting fellow birds, the current outbreak is infecting dairy cows.

In the most recent confirmed human case, the virus spread from a cow to a human; which is the first time cow to human transmission has happened. The last time a human tested positive for H5N1 was in April 2022 in Colorado when an individual got infected from poultry. As Salon previously reported, one major concern is that the more it jumps from animal to animal, or animal to human, the more likely it is to mutate to become more effective at infecting humans.

Jetelina said at the moment, infectious disease experts are “pretty much blind” to how big the outbreak is, and that the discovery of viral fragments in milk suggests it’s more widespread among dairy cows. Another clue the bird flu is more widespread is genomic surveillance that suggests the spillover to dairy cows started in December of last year despite the outbreak being detected at the end of March.

Part of the issue is that testing animals is voluntary at the moment. According to APHIS, the agency is recommending a voluntary testing approach instead of a mandatory one for cattle. The agency says it wouldn’t be “practical, feasible or necessarily informative to require mandatory testing.” For context, the agency stated, there are more than 26,000 dairy herds nationwide and it’s still a small portion that’s infected. However, if cows are going to be moved between state lines the USDA is requiring testing.

However, Dr. Rajendram Rajnarayanan of the New York Institute of Technology campus in Jonesboro, Ark., told Salon testing is still voluntary for the most part and there needs to be comprehensive guidelines on what a common citizen should know, as well as the cattle ranchers.

“Mandatory tests for cattle that are transported is a welcome move. I’d strongly recommend them to include a period of quarantine and retesting before integrating them into the existing herd,” Rajnarayanan said. “The recent data about commercial milk samples testing positive for H5N1 fragments suggests a much wider spread of H5N1 among dairy cattle. Several cows are asymptomatic [but] they still spread the virus to others.”

He added there is no guidance on asymptomatic cattle testing either. However, dairy farmers, Rajnarayanan said, will likely see signs that their herds are infected without testing. In the confirmed infected cows with H5N1, their milk production dropped and turned yellowish. “But what about beef cattle?” Rajnarayanan asked.

Dr. Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization, told Salon via email that more testing needs to be done — especially among asymptomatic cows, beef cattle and cows in states with no known cases. Testing people in contact with animals and testing other animals is “essential.” Serology testing to see evidence of previous infections would be helpful, too.

“In addition, we need complementary lab research to show how tissues of the cow can be infected and more epidemiological data to better understand transmission routes,” Rasmussen said. “Above all, we need more data on virus sequences and sample collection/analysis to date from USDA and other government agencies to better direct our efforts.”

When asked if more humans could be infected, Rasmussen said “this is definitely possible.” But she said it is challenging to assess since the one cow-to-human case was mild and not a respiratory infection.

“As well as the fact that many people at the greatest exposure risk may be undocumented, discouraged from reporting by their employers, and not have access to health care,” she added.

Some public health experts are concerned that human cases are flying under the radar, likely because they are asymptomatic, highlighting anecdotes about dairy workers who have pink eye and other symptoms, but are avoiding testing or being seen by doctors. Earlier this week, James Lowe, a researcher who specializes in pig influenza viruses, told ScienceInsider, “I believe there are probably lots of human cases.”

Rajnarayanan told Salon he is cautious to categorize the current outbreak as “mild” and downplay it despite it not being an immediate risk to humans right now. He added that if public health experts learned anything from the COVID-19 pandemic, it’s that if you keep saying “everything is mild” then “the common people tend not to pay attention at all.” He added the biggest concern is that officials are missing other infections among other species, like pigs. The goal should be to contain the virus as much as possible to keep it from mutating and evolving into something worse.

“The moment it hits species like pigs, it can produce all this reassortments from coinfected viruses; that’s when we’ll have problems,” Rajnarayanan said. “Then it will be better adapted to mammalian species.”

Jetelina agreed.

“The more this spreads, the more it jumps from animal to animal, the more ability it has to mutate,” Jetelina said. “I think that it’s a good sign that we haven’t seen more human cases, we haven’t seen any human clusters, but that doesn’t mean that it can’t happen — the flu is incredibly unpredictable and we need to treat it with urgency and transparency.”