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Foodborne risk for bird flu may be less of a risk than previously thought. But there is still a risk, scientists say. So, we shouldn’t let our guard down just yet. It is just that consuming the virus likely produces milder symptoms than respiratory exposure.
That is what a recent study out of the National Institutes of Allergy and Infectious Diseases explains in a paper published in Nature.
Using monkeys as a model, experiments showed less of a foodborne risk for bird flu when compared to other modes of transmission.
But first, let’s chat about the current bird flu situation.
Highly pathogenic avian influenza (HPAI) H5N1 virus, better known as bird flu, has been in the news since early 2022. What started out as a concern for wild aquatic birds and poultry throughout the United States has begun to spill over into many other mammalian species.
In March 2024, everything changed.
Bird flu was detected in dairy cows in Texas.
Yes. You read that right. Bird flu in dairy cows.
And then people started getting sick. With bird flu. From dairy cows.
Curiouser and curiouser…
The current bird flu situation paints a bigger picture. It seems the threat of bird flu in humans could be more significant from cows than from birds. Meat from beef and chicken as well as poultry eggs are generally consumed cooked. So, heat treatment, theoretically, should kill any potential viral contamination.
But with raw milk consumption rising in popularity, concern over foodborne risk for bird flu in this non-heat-treated product also grows.
The number of people who have had bird flu since this phenomenon began, while important, is just part of the question you should be asking. That number comes to 67 confirmed cases in the United States, by the way.
So, what’s the more important question?
How did they get infected?
Those statistics may surprise you.
Only 23 of these cases (plus another five probable cases) were the result of poultry farm exposure. This only accounts for around a third of the total cases.
The majority of the human cases of bird flu were the result of dairy cattle. Over half (59%) of all human cases of bird flu could be traced back to dairy cattle. This included 40 cases (plus one probable).
One case was traced back to “other animal exposure” and three others (plus one probable) have still unknown source.
A recent study exposed monkeys to bird flu using various modes of transmission to better understand what happens if you consume the virus instead of inhale it.
Scientists have been trying to determine how cow-to-human transmission is occurring. Since human subjects aren’t typically used in studies like this, a surrogate was chosen.
Cynomolgus macaques monkeys were the subject of this experiment. This subject was chosen as a surrogate for humans due to the similar way their bodies react to pathogens compared to humans and often used in similar experiments.
The study included a viral dose close to what has been observed in raw milk samples. A total of 18 macaques monkeys were inoculated in three different ways.
Six were inoculated intranasally to mimic an upper respiratory tract infection. Another six were inoculated in the windpipe (intratracheal route) to mimic a lower respiratory tract infection And the final six were inoculated in the mouth and stomach (orogastric route) to mimic consuming food containing the virus.
In 14 days, symptomatic data was compared.
Monkeys subjected to lower respiratory tract exposure experienced systemic infection with severe pneumonia.
Those who were subjected to upper respiratory track exposure experience mild-to-moderate pneumonia.
But the macaques subjected to mouth or stomach exposure experienced no signs of illness despite limited infection in the body.
All monkeys, even those who consumed the virus, showed evidence of oral shedding. Even limited nasal shedding. Those inoculated in the nose and windpipe, did show higher and prolonged shedding though. Even those who consumed the virus demonstrated some degree of shedding.
“Overall, our study shows that lower and upper respiratory tract infection can lead to systemic virus replication, virus shedding and pneumonia with varying degrees of disease outcome,” the study authors wrote. “In contrast, orogastric exposure led to virus infection, reduced virus shedding and subclinical disease.”
While this study weas a model to examine foodborne risk or bird flu associated with drinking raw milk, researchers caution that the surrogate is just a model. “To what extent it recapitulates human infection remains, as yet, unclear.”
Bird flu is often referred to as “highly pathogenic.” But that categorization applies to poultry, rather than humans.
Most human infections are mild. However, there have been reports of moderate human infection.
Respiratory exposure of bird flu often reveals itself first as eye symptoms. Redness and irritation are often observed around one to two days after exposure. Other respiratory symptoms generally come onboard in about three days (somewhere between two and seven days).
Common symptoms associated with mild bird flu may include:
In some cases, mild illness symptoms can include diarrhea, nausea, or vomiting.
Moderate to severe bird flu symptoms may include:
These symptoms generally last somewhere between a few days to less than two weeks. Though this could vary from person to person. Those with severe illness or complications may be sick for several weeks.
Moderate to severe illness may cause certain complications.
These complications may include:
While human-to-human bird flu transmission has not been well documented, it is theoretically possible and often compared to seasonal flu.
According to the Centers for Disease Control and Prevention (CDC), people are thought to be most contagious during the early part of their illness (the first few days).
Those with higher levels of virus in their lower respiratory tract, likely hospitalized for severe illness or pneumonia, may be contagious for several weeks.
Even those who are infected by not experiencing symptoms could still be contagious, as viral shedding has been observed in asymptomatic subjects.
If you’d like to know more about food safety topics in the news, like “New Study Shows Less Foodborne Risk for Bird Flu Than Previously Thought,” check out the Make Food Safe Blog. We regularly update trending topics, foodborne infections in the news, recalls, and more! Stay tuned for quality information to help keep your family safe, while The Lange Law Firm, PLLC strives to Make Food Safe!
By: Heather Van Tassell (contributing writer, non-lawyer)
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