“We were incredibly surprised. Rather than replicating in the respiratory tract as we had assumed, the virus was actually replicating in the intestinal tract of the birds, which led to them excreting it in their feces and contaminating the water,” explained Webster, now 92 and retired, but still participating in collection trips whenever possible. The feces, known as guano, from infected birds were found to be rich in viruses. Almost all known influenza subtypes have been detected in birds, with only two subtypes being exclusive to bats.
During his initial expedition to the Delaware Bay in 1985, Webster and his team discovered that 20% of the bird feces samples they gathered contained influenza viruses. This realization led them to recognize the area as an ideal location to monitor the spread of flu viruses carried by birds along the Atlantic flyway, spanning from South America to northern Canada. Detecting a new flu virus in this region could provide an early warning of an impending outbreak.
The project, now overseen by Dr. Richard Webby, has evolved into one of the most enduring influenza surveillance initiatives focusing on the same bird populations globally. Dr. Webby heads the World Health Organization’s Collaborating Center for Studies on the Ecology of Influenza in Animals at St. Jude. Predicting pandemics, as described by Webby, is analogous to forecasting tornadoes, requiring a deep understanding of the current baseline to detect deviations, such as host shifts and the driving forces behind these changes.
The United States is currently experiencing a significant transition. Prior to the arrival of the St. Jude team in Cape May this year, H5N1 was detected for the first time in dairy cattle in Texas. This novel finding raised concerns among flu experts like Webby since H5N1 had not previously been known to infect cows. While some flu viruses cause mild symptoms or no symptoms in birds, H5N1, categorized as highly pathogenic avian influenza (HPAI), can have devastating effects on bird populations, leading to mass culling to prevent further spread and alleviate animal suffering.
Despite effective containment measures taken during previous outbreaks, such as the introduction of H5N8 viruses to North America by migrating birds in 2014, the same level of success has not been achieved with H5N1. The virus arrived in the US in late 2021 and has persisted despite extensive culling of infected poultry. Furthermore, H5N1 has developed the ability to infect various mammals like cats, foxes, otters, and sea lions, raising concerns about potential human transmission.
Although H5N1 can infect humans, the current strains do not spread efficiently between people due to differences in receptor cells in the respiratory systems of birds and humans. However, this could change rapidly. A recent study published in the journal Science highlighted a critical shift that could significantly impact the transmissibility and potential threat of the virus.
The ability of the virus to attach onto cells in the human lungs is facilitated by its genetic modification. The team at Cape May had not previously detected the H5N1 virus in the birds they sampled there. However, with the virus spreading among cows in various states, they were curious about its potential presence in other locations. This led McKenzie and Seiler to carefully explore the boggy beach during the spring. Clad in boots, gloves, and face masks, they collected fresh white guano samples using swabs and deposited them into vials. These samples were meticulously stored in trays and a cooler for further analysis. Throughout the week, the team gathered 800 to 1,000 samples to be sequenced and uploaded to an international database for tracking influenza strains globally.
The team focused on different bird species, with seagulls and sandpipers yielding distinct samples. A separate study was planned for seagulls as specific viruses had only been found in them. The team also observed dunlins searching for crab eggs nearby. Some samples were sent to Memphis, Tennessee, while others were taken to an RV park where Dr. Lisa Kercher was stationed with her mobile lab. Kercher’s aim was to expedite the screening process to identify influenza viruses in the field, potentially speeding up the overall analysis timeline.
Despite comprehensive sequencing efforts, the H5N1 virus was not detected in the Cape May or Canadian duck samples this year, leading to continued curiosity among the team. After completing their work in Cape May, Kercher transported the mobile lab to the Peace River in northern Alberta, Canada, for testing ducks preparing to breed. This marked the team’s first use of the mobile lab on this long-standing research trip to Canada.
After her trip to Alberta, Kercher drove her RV to Tennessee to test more ducks in their winter hibernation grounds. Meanwhile, a virus was spreading among herds of cows in the Midwest and California. Although some farmworkers became infected, there was no evidence of human-to-human transmission. The cattle outbreaks briefly slowed down before cases of serious human infections surfaced.
The first case was a teenager in Vancouver hospitalized with respiratory distress, followed by a person in Louisiana falling seriously ill with H5N1 after contact with a backyard flock. These cases involved a different virus genotype than the one in cows. The cattle virus belonged to the B3.13 genotype, while the human infections were linked to the D1.1 genotype found in wild birds and poultry.
The St. Jude team, after missing the virus in earlier seasons, moved their mobile lab to a wintering ground for ducks in Tennessee. They discovered the D1.1 genotype in several duck samples, linking the virus to the Mississippi flyway.
This newer virus group has raised questions among scientists, prompting further analysis of surveillance data to understand its emergence and transmission patterns. Recent surveillance data contributed to a study led by Dr. Louise Moncla at the University of Pennsylvania, revealing multiple introductions of the virus by wild birds along migratory pathways.
The study suggests that wild birds serve as a reservoir for the virus, complicating efforts to control outbreaks through culling. Monitoring and surveillance of migrating birds are deemed crucial in preventing future outbreaks. Webby’s team plans to continue their surveillance efforts to stay ahead of potential risks.
As the sun rises over the Delaware Bay, scientists anticipate the return of an annual phenomenon. Kercher observes that the patterns observed in the Delaware Bay this year align closely with those witnessed over the past four decades. Specifically, shore birds play a critical role in the long-distance transmission of viruses. These birds make a pit stop in the Delaware Bay to refuel, inadvertently facilitating the spread of viruses during their temporary stay before carrying them to new locations.
The uncertainty surrounding the future remains palpable. The looming question remains: will the H5N1 virus undergo significant mutations to pose a threat to human populations? Kercher underscores the importance of vigilance in monitoring the situation closely. The implications of a potential shift in the virus’s behavior are profound, necessitating a proactive stance in response to emerging developments.
