Although many avian influenza viruses cause only mild disease, Highly Pathogenic Avian Influenza (HPAI) is often fatal in birds and is known to sporadically spillover to mammals. Avian influenza viruses can become highly pathogenic in birds when one of the surface proteins, known as hemagglutinin (HA), acquires a mutation that allows greater viral spread throughout the host.1 Increased spread of these viruses increases the chances that they will acquire genomic variations that lead to highly pathogenic forms. Historically, the spread of HPAI H5 and H7 subtypes have resulted in great economic loss due to the severe disease and death they cause in domestic poultry. To date, however, HPAI have rarely infected mammals and have very limited capacity to be transmitted from human to human, with nearly all documented human cases resulting directly from close contact with infected birds. Confirmed HPAI H5N1 infections in humans since 2003 have resulted in a greater than 50% case fatality rate. Due to the high mortality rates and concerns over their potential to cause a pandemic, HPAI and their spread through wild bird and mammal populations are under close surveillance.
Since late 2020, HPAI H5N1 has devastated the U.S. poultry industry causing almost 60 million poultry deaths and has led to renewed conversations about whether preventative commercial poultry vaccination programs should be undertaken.2 Further, HPAI has infected wild bird populations at an alarming rate. Current reports from the World Animal Health Information System (WAHIS) sit at around 68,000 wild bird casualties, though due to less surveillance in wild populations some experts estimate the true extent of wild bird mortality in the millions.3 Recent reports of HPAI H5N1 spillover into mammals has increased concerns and scientific dialogue about the pandemic potential of HPAI and prevention strategies.4 Dr. Jonathan Runstadler, of Tufts University and member of the Center for Research on Influenza Pathogenesis and Transmission (CRIPT), found a large mortality event of over 300 harbor seals in New England attributed to HPAI. As reported by the New York Times (NYT), the recent avian influenza outbreak is the largest in U.S. history and has led to increased monitoring efforts by the Centers for Disease Control (CDC) in cooperation with state and local public health departments. Additionally, the recent outbreak has led to increased poultry vaccine testing by the federal Agriculture Department. Dr. Anice Lowen, Principal Investigator of Emory University CEIRR (Emory-CEIRR), mentioned to the NYT that vaccinating poultry could “reduce the potential for viral evolution,” which may limit new HPAI H5N1 variants and “exposures to humans.”2 Dr. Richard Webby, Principal Investigator of St. Jude CEIRR (SJCEIRR), told the NYT that avian influenza “is here to stay” in the US, highlighting the need for mitigation efforts.2 The Washington Post recently reported that agriculture officials in the Biden Administration are testing four avian influenza vaccines in poultry to mitigate transmission at farms and minimize economic consequences such as rising egg prices.2,5
It is important to acknowledge that even with the current spread of HPAI H5N1 within commercial bird populations, transmission to humans has remained incredibly rare and there have been no recorded cases of human-to-human transmission from this outbreak. An article recently published in Nature by Dr. Florian Krammer, CRIPT, and Dr. Stacey Schultz-Cherry, co-Principal Investigator of SJCEIRR, provides an overview of the past HPAI outbreaks and frames the current and future risks posed by HPAI. The authors emphasize that, although the apparent spread of H5N1 viruses between mammals does increase concerns over the possibility that the same viruses could acquire the ability to transmit between humans, it is still “not a reason for panic”.1 The authors point to antivirals that can target H5N1 influenza viruses, providing as a potential immediate treatment option, as well as seasonal exposure to the N1 neuraminidase (NA) component of the viruses, which likely provides partial immunity to the adult population. Nevertheless, Dr. Krammer and Dr. Schultz-Cherry suggest pandemic risk reduction actions should be undertaken including efforts to increase public awareness, informing physicians to be vigilant about monitoring influenza infections, starting production and stockpiling of H5N1 vaccines, and scrutinizing safe farm practices.
To read more about the HPAI H5N1 outbreaks, check out:
2 The New York Times: U.S. Considers Vaccinating Chickens Amid Bird Flu Outbreak
5 The Washington Post: Biden administration tests vaccines to fight avian flu that sent egg prices soaring