The US Department of Agriculture made a startling announcement on Wednesday, revealing that the H5N1 bird flu virus has been identified in a pig from a farm situated in Crook County, located in the heart of central Oregon. This marks an unprecedented moment, as it is the first confirmed instance of a pig in the United States being infected with this particular strain of the virus. While the specific genetic sequence associated with this outbreak has not yet been disclosed to the public, the Oregon Department of Agriculture (ODA) has assured the media that it bears no relation to the strain currently affecting dairy cattle in the region.
In a troubling turn of events, the infected pig was euthanized, and an autopsy revealed that the virus had spread throughout its body, as noted by state veterinarian Ryan Scholz. In response to the outbreak, a total of five pigs, along with 70 chickens, ducks, and geese from the same farm, were culled as a precautionary measure to mitigate the risk of further contagion from this highly transmissible virus. The farm is currently under quarantine as thorough surveillance efforts are underway to monitor the situation. Authorities suspect that the outbreak may have been triggered by exposure to infected waterfowl.
Reports indicate that poultry and pigs had been housed together on the property, heightening concerns among experts who addressed the media after the announcement. They underscored the significant implications of the virus’s presence in pigs, given that these animals are known to be vulnerable to infections from both avian and human pathogens. This susceptibility raises alarm bells, as it creates an environment conducive to the genetic reassortment of viruses, potentially resulting in the emergence of new hybrid strains. Dr. Dean Sidelinger, an epidemiologist with the Oregon health department, expressed legitimate concerns, stating, “We do worry about changes in this virus.” However, he attempted to alleviate fears by asserting, “The risk to the public remains low.”
Despite Dr. Sidelinger’s reassurances, scientists conversing with STAT News expressed a more cautious outlook, eagerly awaiting additional details concerning the ongoing investigation. Dr. Florian Krammer, a prominent flu virologist at Mount Sinai’s Icahn School of Medicine, acknowledged that if the virus did not begin to transmit among pigs and was contained to the one farm, it would not pose a significant risk. Yet he stressed, “If it starts to spread from pigs to pigs, then it’s much more of a problem. If it ends up in large pig populations in the U.S., similar to cows, I think this would be a disaster.”
This emerging outbreak of the H5N1 bird flu virus among dairy cattle was first reported in March of this year and has since infiltrated 14 states, affecting a staggering 404 dairy cattle herds. Originally centered in Colorado, the outbreak has recently shifted to California, where 202 cattle herds have been impacted, with a concerning 158 of those cases emerging within just the last month.
The total number of human cases of H5N1 now stands at 39, with 20 of these infections occurring among dairy cattle handlers. A concerning 16 infections have been documented among workers in California. In addition, 18 poultry workers have also tested positive for H5N1, with nine of these cases identified in Colorado. The Centers for Disease Control and Prevention (CDC) has only conducted testing on approximately 300 individuals, while keeping a watchful eye on over 6,100 people who may have been exposed.
Compounding the seriousness of this situation, the origin of an H5N1 case in Missouri remains a mystery, further intensifying concerns regarding the possible human-to-human transmission of the virus. Coupled with the escalating number of infections among livestock and their handlers, fears about the potential emergence of a novel H5N1 bird flu pandemic are starting to loom larger on the public health horizon.
The inclusion of pigs in this mix raises the concerning possibility of developing a pandemic pathogen. Dr. Thomas Peacock, an expert in influenza viruses at the Pirbright Institute in the UK, commented on the gravity of the situation. He remarked, “Pigs are absolutely full of influenza viruses that in the past were human seasonal influenza viruses or human pandemic influenza viruses. So, they have a really, really rich genetic material in them.” This capability positions pigs as potential mixing vessels for avian and human influenza viruses, allowing for genetic exchange that could lead to more dangerous strains.
The April 2024 edition of the CDC’s journal Emerging Infectious Diseases issued a grave warning regarding the emergence of H5N1 among swine. The journal stated, “If an avian [Influenza A Virus] strain, such as H5Nx 2.3.4.4b, successfully infected domestic swine, pig-to-pig transmission, reassortment with endemic swine IAV, or acquisition of adaptive mutations that might enable an avian-to-mammalian switch could potentially occur. Continued circulation in the wild bird population and peridomestic wild mammal infections elevate the risk for exposure of swine because of the current outbreak’s wide distribution in states with large pig populations.”
Dr. Webby, speaking to Scientific American, elaborated on the criteria necessary for a pandemic virus to arise, stating that it would require more than a simple reassortment of the circulating strains. “It’s going to take reassortment, followed by some critical mutations in [one specific] gene,” he explained. This implies that the virus may need to adapt to spread beyond the conjunctiva of the eyes to infect the respiratory tract, thereby transmitting through airborne aerosols, significantly increasing its potential to infect humans.
He further cautioned, “[The] hurdles are high that this virus has to overcome to become a human virus. But anything that gives it more opportunity to do so is obviously a concern—whether that’s just more human infections from farm animals or the potential of reassorting with a human seasonal virus. All of those things would increase the risk.”
Although current cases among agricultural workers have not resulted in severe illness, troubling laboratory experiments using isolates from these strains have produced alarming results. A recent study published in the journal Nature, led by Dr. Yoshihiro Kawaoka and his team from Wisconsin, showed that the bird flu virus isolated from an eye of an infected animal handler in Texas demonstrated efficient spread in human respiratory cells and proved lethal in both mice and ferrets. The research showed the virus was capable of spreading via aerosol to other animals, resulting in lethal outcomes. The researchers underscored the urgent need for containment measures, stating, “Based on these observations, every effort should be made to contain HPAI H5N1 [bird flu virus] outbreaks in dairy cattle to limit the possibility of further human infections.”
In another important study conducted by CDC investigators employing ferrets as a model to evaluate the bird flu virus’s pathogenicity, the researchers reported significant findings. They revealed the TX/37 strain displayed exceptional potential for systemic infection in ferrets, leading to high levels of viral shedding and infection among naïve contacts. Ferrets exposed to TX/37 quickly developed severe and fatal illness, exhibiting both viremia and extrapulmonary spread. The study also confirmed that the virus was capable of airborne transmission, albeit at lower levels compared to highly transmissible human seasonal and swine-origin H1 subtype strains. The results underscored the heightened virulence, transmissibility, and airborne shedding of the virus, emphasizing the imperative for continued public health vigilance.
These alarming developments necessitate widespread discussion and communication with agricultural workers and the general public. Public health cannot afford to be confined to scientific conferences and academic journals; it requires urgent action from local and federal authorities to avert the emergence of the next pandemic. A wait-and-see approach is both imprudent and fraught with potentially dire global consequences.
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**Interview: Understanding the Implications of H5N1 in Pigs — A Discussion with Dr. Ryan Scholz, State Veterinarian**
**Editor:** Thank you for joining us today, Dr. Scholz. The announcement made by the USDA regarding the H5N1 bird flu virus being found in a pig in central Oregon is unprecedented. Can you walk us through the immediate steps taken following this discovery?
**Dr. Scholz:** Absolutely, and thanks for having me. Once we confirmed the infection in the pig, our first priority was to contain the virus. The infected pig was euthanized and underwent an autopsy, which indicated that the virus had disseminated throughout its body. As a precaution, we culled the five pigs and 70 poultry on that farm. The farm is currently under quarantine, and we are actively monitoring the situation.
**Editor:** Given this is the first recorded case of H5N1 in pigs in the U.S., what does this mean for public health and agriculture?
**Dr. Scholz:** It’s indeed a significant finding. H5N1 has primarily been a concern in poultry, but its presence in pigs raises alarms due to their susceptibility to a wide range of pathogens, including both avian and human viruses. While we recognize the situation’s seriousness, I want to emphasize that the Oregon Department of Agriculture has assured us there is currently no threat to public health.
**Editor:** Dr. Dean Sidelinger expressed concerns about potential changes in the virus, while also noting that the public risk remains low. How do you assess the risk of the virus mutating or spreading, especially among pig populations?
**Dr. Scholz:** There’s always a degree of uncertainty when dealing with viruses, particularly when one like H5N1 appears in a new animal host. If the virus were to begin transmitting among pigs, that could certainly escalate the concerns. But right now, our focus is on preventing that occurrence through strict biosecurity measures. Surveillance is crucial, and we’re working closely with federal and state health authorities to monitor any developments.
**Editor:** Experts have talked about the potential for pigs to act as “mixing vessels” for viruses. Should the public be concerned about the possibility of a new hybrid strain emerging?
**Dr. Scholz:** It’s a valid concern. Pigs are capable of harboring various forms of influenza, which can lead to genetic reassortment. However, we are actively engaged in research and surveillance to ensure that we detect any changes early. The goal is to prevent any scenario where the virus could adapt to spread among humans.
**Editor:** With reports of human infections related to H5N1 in agricultural settings, what precautions is the CDC taking, and how are farm workers being kept safe?
**Dr. Scholz:** The CDC is actively monitoring potential human exposure and testing individuals who may have come into contact with infected animals. Farm workers are advised to use proper protective equipment, practice good hygiene, and report any illness immediately. Awareness and education are key in minimizing risks.
**Editor:** Lastly, how optimistic are you about managing this situation and preventing a larger outbreak?
**Dr. Scholz:** While the situation is serious, we have robust systems in place to respond to outbreaks and monitor animal health. Collaboration between state and federal agencies, along with the expertise of veterinarians and epidemiologists, strengthens our ability to manage situations like this effectively. Our hope is to contain this outbreak swiftly, minimizing implications for public health and agriculture.
**Editor:** Thank you, Dr. Scholz. Your insights are invaluable as we navigate these complex public health issues.
**Dr. Scholz:** Thank you for having me.
