Understanding the Risks of Bird Flu in Poultry, Cattle, and Humans

The confirmation from the Department of Agriculture regarding the H5N1 bird flu virus infecting dairy cows across the country has sparked widespread media attention. Nirav Shah, the principal deputy director at the Centers for Disease Control and Prevention, revealed that tests have identified the virus in cattle from nine states, predominantly in Texas and New Mexico, with the most recent case reported in Colorado. Shah made these remarks during a May 1 event at the Council on Foreign Relations.

Apart from dairy cows, a variety of other animals, including at least one person in Texas, have also been infected by H5N1. However, scientists’ primary concern revolves around the potential efficient transmission of the virus from person to person. As of now, such transmission has not occurred, and Shah stated that the CDC currently considers the H5N1 outbreak to pose a low risk to the general public.

It is important to note that viruses evolve rapidly, and outbreaks can undergo rapid shifts. Shah likened the speed of this outbreak to that of a bullet train, emphasizing that the information available today represents only a snapshot of the fast-moving situation. Therefore, what is presently known about the H5N1 bird flu is likely to change.

To help you stay informed, KFF Health News provides an overview of the essential information you need to know at this time.

Who is susceptible to bird flu infection?

While bird flu primarily affects birds, there has been a concerning trend in recent years where the H5N1 bird flu virus has crossed over from birds to mammals worldwide. This phenomenon has resulted in infections in an expanding range of species, numbering more than 50. Among these species are seals, goats, skunks, cats, and even wild bush dogs at a zoo in the United Kingdom. Disturbingly, outbreaks of H5N1 bird flu caused the deaths of approximately 24,000 sea lions in South America last year. This highlights the ability of the virus to infect and impact various mammalian species beyond its avian origins.

The current outbreak of bird flu in cattle is distinct due to its rapid transmission from one cow to another, which sets it apart from previous cases, with the exception of infections observed in sea lions. The similarity in genetic sequences of H5N1 viruses obtained from cattle indicates this widespread transmission.

The situation with the cattle outbreak is alarming because it has caught the country off guard. Researchers studying the genomes of the virus suggest that it originated from birds and crossed over to cows in Texas towards the end of last year. Since then, the virus has spread among a significant number of cows, far surpassing the extent of testing conducted thus far.

The revelations from analyses conducted by experts indicate that the virus has been circulating among cows for approximately four months without detection, right under our noses. This highlights the need for increased surveillance and vigilance to identify and address such outbreaks promptly. Michael Worobey, an evolutionary biologist from the University of Arizona in Tucson, emphasized the surprising nature of the situation.

Analyzing the Potential for a New Pandemic: Assessing the Current Situation

While the possibility of a bird flu pandemic is not imminent, it is an important consideration due to the potential devastating consequences it could bring. Historical data reveals that older strains of H5N1 bird flu viruses, spanning from 2003 to 2016, resulted in a mortality rate of over 50% among infected individuals. Even if the current H5N1 strain circulating in cattle proves to have lower death rates, the repercussions could still involve a significant number of people falling ill, potentially overwhelming hospitals and diverting resources from other critical medical emergencies. It is crucial to acknowledge the potential severity of such a scenario and take proactive measures to prevent the spread of the virus, mitigate its impact, and ensure healthcare systems are prepared to handle any potential outbreak effectively.

While there have been isolated cases of H5N1 infection in humans this year, the current state of the virus does not pose an immediate pandemic threat. To reach such a catastrophic status, a pathogen must be capable of causing widespread illness across multiple continents. This requires the H5N1 virus to infect a large number of individuals, which is unlikely to occur through sporadic spillovers from farm animals to humans.

For the H5N1 virus to trigger a pandemic, it would need to acquire specific mutations that enable it to spread efficiently from person to person, similar to seasonal flu. This would involve respiratory transmission through coughing, sneezing, and breathing, making it highly contagious. As we witnessed during the depths of the Covid-19 pandemic, airborne viruses are challenging to contain.

However, the current situation provides ample opportunities for H5N1 viruses to undergo evolutionary changes while replicating within thousands of cows. Like all viruses, they mutate during replication, and mutations that enhance their survival are passed on to subsequent generations. As cows are mammals, the viruses may adapt better to thrive within cells that resemble our own more closely than those of birds.

The evolution of a bird flu virus capable of causing a pandemic could be facilitated by a phenomenon known as reassortment, wherein viruses exchange genetic material with other strains. In a study published in 2009, researchers, including Michael Worobey, traced the origin of the H1N1 “swine flu” pandemic to instances where different viruses causing swine flu, bird flu, and human flu mixed and matched genes within co-infected pigs. Worobey cautioned that pigs might not necessarily play a role in any potential future events.

While the conditions for the emergence of a pandemic-ready bird flu virus exist, it is important to note that it has not occurred yet. Continued surveillance, research, and preparedness measures are vital to monitor the virus’s evolution and prevent the potential development of a pandemic strain.

Potential Risks of Consuming Virus-Contaminated Milk: Understanding the Implications

Commercially sold cow’s milk, including powdered milk and infant formula, is considered safe for consumption due to mandatory pasteurization requirements imposed by law. Pasteurization involves subjecting milk to high temperatures, effectively eliminating bacteria, viruses, and other microorganisms. While fragments of H5N1 viruses have been detected in milk samples from grocery stores, it has been confirmed that these viral particles are inactive and pose no harm.

On the other hand, it has been demonstrated that unpasteurized “raw” milk can contain viable H5N1 viruses. Consequently, health authorities such as the FDA strongly advise against consuming raw milk. Consuming unpasteurized milk can lead to severe illness or worse. However, even in such cases, the likelihood of a pandemic being triggered is low because the current form of the virus does not possess efficient person-to-person transmission capabilities, as observed in seasonal flu strains.

Recommended Actions and Strategies in Response to a Situation

The spread of H5N1 bird flu in cattle has been significant due to insufficient surveillance measures implemented by the U.S. Department of Agriculture (USDA) and other relevant agencies. This lack of monitoring has allowed the virus to propagate unnoticed within cattle populations. To address the situation, the USDA has recently issued an order requiring testing of all lactating dairy cattle before their movement to other states, with a mandate to report the test results.

However, similar to the early stages of the Covid-19 pandemic when testing was limited to international travelers, focusing solely on testing cows that cross state lines would likely result in numerous cases going undetected. This approach would overlook many instances of H5N1 infection within cattle that remain within a single state or region.

The current limited testing approach fails to provide insights into how the H5N1 virus is spreading among cattle, which is crucial information for farmers to effectively control its transmission. One leading hypothesis suggests that the virus may be transmitted from one cow to another through the milking machines.

To enhance testing efforts, Fred Gingrich, the executive director of the American Association of Bovine Practitioners, proposes that the government incentivizes cattle farmers by offering funds when they report cases, encouraging them to conduct testing. Without such incentives, reporting only adds to the financial losses and reputational damage experienced by farmers.

Gingrich highlights the significant economic impact of these outbreaks, with farmers experiencing a decrease of approximately 20% in milk production as animals eat less, produce less milk, and some milk becomes abnormal and unsellable.

While the government has made H5N1 tests free for farmers, Gingrich notes that there is no budget allocated for veterinarians who are responsible for sampling the cows, transporting samples, and completing paperwork. According to him, tests are the least expensive part of the process.

If on-farm testing remains challenging, evolutionary virologists can still gain valuable insights by analyzing the genomic sequences of H5N1 viruses sampled from cattle. Differences in these sequences can provide information about the origins of the current outbreak, its path of transmission, and whether the viruses are acquiring mutations that could pose a threat to humans. However, the USDA’s slow and incomplete posting of genetic data has hindered this crucial research, as noted by Michael Worobey.

Additionally, the government should assist poultry farmers in preventing H5N1 outbreaks, as they can cause significant bird fatalities and pose a continuous risk of spillover. Waterfowl, such as ducks and geese, are often the sources of outbreaks on poultry farms, and remote sensing and similar technologies can help detect their proximity. By focusing on potential spillover zones, farmers can implement targeted measures such as routine surveillance, using water cannons to deter migrating flocks, relocating farm animals, or temporarily confining them in barns. Prioritizing prevention measures and allocating resources accordingly is crucial, as emphasized by Maurice Pitesky, an avian disease specialist at the University of California-Davis.

Assessing the Risks of H5N1 Bird Flu for Humans

The current understanding of H5N1 bird flu transmission among farmworkers remains limited. In Texas, only one person has been diagnosed with the disease this year, specifically in April. This individual had close contact with dairy cows and experienced a mild case with an eye infection. The detection of this case was made possible through the surveillance process of the Centers for Disease Control and Prevention (CDC).

According to the established procedure, clinics are responsible for notifying state health departments when they diagnose farmworkers with the flu using broad influenza virus tests. State health departments then confirm the diagnosis and, if it is positive, send the person’s sample to a CDC laboratory for specific testing for the H5N1 virus. So far, the CDC has received 23 samples, of which all but one tested negative.

State health departments are actively monitoring approximately 150 individuals who have been in close proximity to cattle. These farmworkers are being contacted through phone calls, text messages, or in-person visits to check if they develop any symptoms. If symptoms do arise, they will undergo testing.

Another method to assess farmworkers would involve testing their blood for antibodies against the H5N1 bird flu virus. A positive result would suggest possible prior infection. However, health officials have not yet initiated this specific testing.

Overall, the current knowledge regarding H5N1 transmission among farmworkers is limited, and surveillance efforts are ongoing to identify any potential cases or patterns of infection.