Highly Pathogenic Avian Influenza (HPAI): An Update on Bird Flu

Bird flu has spread its wings, and it's back with a new name: Highly Pathogenic Avian Influenza, or HPAI. The name may sound like it came from a sci-fi thriller, but don't worry — it's still the same old avian influenza we know, just a bit more sophisticated. And while it might be tempting to panic when a virus crosses species (from birds to dairy cows, of all things), a calm, informed approach is the way to go. Let’s break it down, so you can keep your head on straight and not start eyeing every pigeon with suspicion.

HPAI in Context: Understanding the Disease

HPAI, still commonly known as bird flu, is a highly contagious viral disease affecting birds. The “highly pathogenic” tag refers to the severity of disease it causes in birds, not necessarily in humans. The current strain, H5N1, has led to extensive outbreaks in poultry and, more unusually, dairy cattle. While human infections are rare, H5N1 has previously shown a high mortality rate in those affected, which is why public health authorities are monitoring it closely, particularly for any signs it could spread more easily between humans.

Current Human Cases: What We Know So Far

In 2024, there have been 16 confirmed cases of H5 infections in the U.S., almost all involving individuals who work closely with infected animals. Six cases are tied to exposure to dairy cows, and nine to contact with infected poultry. Most patients experienced mild symptoms like conjunctivitis (eye redness) or flu-like symptoms, and no one required hospitalization for severe respiratory illness.

Recently, two new cases were confirmed in California among farm workers in the Central Valley who had contact with infected dairy cows. According to Nirav Shah, the CDC’s principal deputy director, these cases were not unexpected given the outbreaks in animals, and they don’t change the agency’s overall risk assessment for the public, which remains low. The CDC continues to analyze these cases to monitor any changes in the virus, particularly those that could suggest a shift toward human-to-human transmission.

The Missouri Case: A Unique Concern

One case, confirmed in September in Missouri, stands apart. Unlike all other human H5 infections in the U.S., this patient did not have any known exposure to infected animals. The individual was hospitalized due to underlying health conditions but did not have severe flu symptoms. This anomaly has raised questions about how the patient became infected, prompting a detailed investigation.

The CDC is conducting further tests, including serologic testing on healthcare workers who were in contact with the patient to rule out any possibility of human-to-human transmission. While no evidence of this has been found so far, the case remains a focus of active investigation as the CDC awaits more test results, including antibody analyses expected later this month.

Federal Response: Vaccine Production and Preventive Measures

To prepare for any potential need, the U.S. government has invested $72 million to increase the stockpile of H5N1 vaccines for humans, contracting with CSL Seqirus, GSK, and Sanofi to ramp up production. “We do expect that we will have a total of just over 10 million doses filled and finished by the end of the first quarter of calendar year 2025,” said David Boucher, director of infectious disease preparedness at the Administration for Strategic Preparedness and Response. While there is no immediate need for these vaccines, having them on hand ensures rapid deployment should the virus pose a greater threat to humans.

Additionally, Moderna, Pfizer, and GSK are working on mRNA vaccines specifically targeting H5N1, but these remain in the testing phase and are not yet approved for use.

For those working around potentially infected animals, the CDC recommends personal protective equipment (PPE) and biosecurity measures. Seasonal flu vaccination is also advised, not only to protect against typical flu but to reduce the risk of co-infections that could lead to viral mutations.

The “Silo Study”: Investigating H5N1 in Dairy Cattle

H5N1’s jump to dairy cows has prompted federal agencies to launch the “Silo Study,” a nationwide effort to assess the prevalence of the virus in raw cow's milk before pasteurization. Beginning in late October, samples of raw milk will be collected from dairy facilities across the country for testing. The FDA reassures the public that pasteurization effectively kills the virus, so there’s no risk in consuming pasteurized dairy products. However, those who prefer raw milk should be aware of the increased risk, as unpasteurized products can carry infectious pathogens like H5N1.

The data collected from this study will help inform strategies to control the virus in dairy herds and assess any potential risk to the food supply.

Preventive Measures and Public Health Recommendations

For those working closely with poultry or dairy cattle, adhering to the CDC’s guidance on using PPE and practicing biosecurity is crucial. If you develop symptoms like eye redness, flu-like illness, fever, or muscle aches after exposure to potentially infected animals, contact your local health department for testing and advice.

The general public is advised to stick to pasteurized dairy products to reduce any risk of exposure to the virus through food. If you’re a regular consumer of raw milk, consider switching to pasteurized options for added safety during this outbreak.

Looking Ahead: Monitoring and Preparedness

The CDC continues to monitor the spread of HPAI closely, analyzing any genetic changes that could increase the risk of human-to-human transmission. The agency emphasizes that the overall risk to the public remains low. Still, healthcare professionals, particularly those in rural or agricultural regions, should remain vigilant and stay informed on evolving guidelines and best practices for reducing risk.

HPAI has undoubtedly raised the stakes in animal and public health, but with vaccines in production and preventive measures in place, we are better equipped to manage this evolving situation. As we move forward, education, monitoring, and prevention will be key in reducing the spread of HPAI and ensuring the safety of both animals and people.

So, while bird flu may be back with a new name and a wider reach, we’re staying ahead of the curve with informed strategies and preparedness. The path forward is clear: stay informed, take precautions, and, most importantly, don’t let the name change fool you — it’s still just bird flu at its core, and we know how to deal with that.