Since late 20211, the U.S. has experienced a Highly Pathogenic Avian Influenza (HPAI) H5N1 outbreak that has caused tens of millions of commercial poultry deaths. This outbreak has highlighted the importance of animal surveillance efforts, one of the foremost strategies to understand circulating avian influenza viruses and anticipate the potential threats they pose. As part of these surveillance efforts, research scientists annually deploy to areas that have historically exhibited a high prevalence of influenza among susceptible avian species to collect samples from the bird populations, estimate infection rates, and monitor strain evolution.
Delaware Bay is a known hotspot within the U.S. for influenza surveillance. Fecal samples are collected yearly between May and June from the shorebird populations as they migrate to the Arctic from South America. Research teams from St. Jude Children's Research Hospital, the lead institution for the St. Jude Center for Excellence in Influenza Research and Response (SJCEIRR), have visited Delaware Bay for influenza surveillance for over 3 decades. The researchers collect fecal samples to both better understand the currently circulating influenza viruses within the migrating shorebird population and to try to stay a step ahead of potentially deadly, or highly pathogenic, viral strains. The Delaware Bay surveillance efforts are led by multiple SJCEIRR teams within Dr. Richard Webby's lab and are headed by Dr. Pamela McKenzie and Dr. Lisa Kercher. These efforts were recently highlighted in a New York Times (NYT) article2. The St. Jude research teams collaborate with wildlife biologist Dr. Lawrence Niles, who leads conservation efforts through his Wildlife Restoration Projects company, to pinpoint the best collection sites and retrieve their samples. The researchers then utilize various strategies to identify droppings from the appropriate bird species, collect the fecal samples using a swab, store it in a cooler, and analyze each sample back in their Memphis laboratories after the birds have continued their migration. The SJCEIRR researchers described 2023 as a “unique year” to the NYT, donning extra personal protective equipment due to the possibility that avian H5N1 influenza, also called A(H5N1), may show up in their Delaware Bay samples for the first time. As of the most recent collection efforts in 2022, HPAI A(H5N1) has not yet been detected in the South American area that the birds migrate from. The anticipated presence of HPAI A(H5N1) in their avian samples also spurred the SJCEIRR teams to boost their collection efforts from the standard 600 samples to a goal of 1000 samples.
The samples collected from Delaware Bay may be integral to our understanding of what makes the currently circulating A(H5N1) viruses so pathogenic, as well as allow the research community to observe how the viruses are evolving. These data also make studies, such as the one recently published in Nature Communications by Dr. Richard Webby’s group, possible. Kandeil et al. describe how the highly pathogenic A(H5N1) viruses of clade 2.3.4.4b, which are responsible for the recent outbreak, began to rapidly expand in wild and domestic bird populations across multiple continents, including North America, starting in 2021.3 Notably, as the A(H5N1) clade 2.3.4.4b spread intra-continentally in North America it mixed with other influenza viruses circulating in North American wild birds, which broadened the lineage’s genetic and phenotypic diversity. The authors express that concern is warranted based on their findings that a variety of HPAI A(H5N1) 2.3.4.4b viruses exhibited increased disease severity with neurologic involvement in the two mammalian models tested, ferrets and mice. Still, the receptor binding properties of the tested viruses show strong avian specificity, greatly inhibiting their ability to spread to mammals. Such work highlights the importance of collecting animal surveillance samples as it can enhance our understanding of how influenza viruses are changing over time, enables scientists to correlate genetic characteristics with disease phenotypes, and informs our estimations of the risks the viruses pose in causing widespread disease.
The unglamorous work conducted by the SJCEIRR teams at Delaware Bay are integral to our understanding of both the current state and potential future trajectory of HPAI viruses. Although the number of humans that have been infected with HPAI viruses remains low, and human to human transmission has not been observed, the high fatality rates associated with human infections makes constant surveillance of emerging HPAI imperative, especially of those that show the proclivity to infect mammalian species.4 Furthermore, the rapid expansion and diversification of HPAI A(H5N1), and specifically clade 2.3.4.4b, suggests it is vitally important that researchers keep close watch through animal surveillance sample collection and analysis. Surveillance efforts ensure that the risk to public health, as well as domestic animal industries, are well understood and guidance is continually updated.
To read more about the HPAI H5N1 surveillance, check out:
1. H5N1 Bird Flu: Current Situation Summary | Avian Influenza (Flu) (cdc.gov)
2. The New York Times: For These Bird Flu Researchers, Work Is a Day at the Very ‘Icky’ Beach
4. Technical Report: Highly Pathogenic Avian Influenza A(H5N1) Viruses (cdc.gov)