A recent editorial published in The Lancet Microbe underscored the ‘One Health’ policy for surveilling emergent infectious diseases.
Eighty-one cases of highly pathogenic avian influenza (HPAI) A subtype H5N6 in humans have been detected to date since the first human case in 2014. Most (68%) of these cases occurred during 2021-22, mainly in China. In contrast, millions of birds died this year due to avian influenza; for instance, more than 40 million birds have been killed in the United States (US) since January 2022.
The incidence of avian influenza is also rising across Europe. The European Center for Disease Prevention and Control (ECDC) reported over 1100 detections of HPAI H5 in birds from March to June 2022. This was a 38% increase from last year during the same period. The increased incidence of HPAI infections, especially H5N6 in humans, is concerning.
The resurgence of H5N6, amid an ongoing pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is opportune as the political appetite and funding for disease surveillance were never so significant. A sentinel surveillance program for influenza has prevailed for decades, even before the coronavirus disease 2019 (COVID-19) pandemic, as shown by the World Health Organization (WHO) Global Influenza Surveillance and Response System (GISRS).
The development of a ‘Pandemic Influenza Preparedness Framework’ is attributed to the GISRS, advocating for the sharing of influenza data, leading to timely interventions such as the rapid development of or access to vaccines. Its role in publishing SARS-CoV-2 sequence data was pivotal, contributing to the fast and impressive rollout of COVID-19 vaccines. Although HPAI viruses could be a significant public health threat, it’s a known threat and thus could be monitored.
Role of genomic surveillance
Since October 2021, all HPAI H5 viruses detected in Europe were of the 18.104.22.168b clade associated with outbreaks in Asia over the past few years. This clade is widespread and appears to be evolving; a recent study from China revealed novel reassortment of H5N6 viruses with other H5 viruses, resulting in newer strains. Antigenically, these strains were distinct from the vaccine used in the poultry industry.
Genomic surveillance programs are essential to decrease reassortment, inform vaccination policies, and preclude spillover into humans. Further, sequencing also revealed the importation of a novel reassortment of H5 genotypes into the US and Europe, perhaps due to the migration of birds. Therefore, metagenomic sequencing of HPAI infections in humans might not be sufficient to curb avian influenza in humans.
One Health approach
The need for a ‘One Health’ approach for the surveillance of emergent infectious diseases has been well established. The Wildlife Conservation Society released the Manhattan principles in 2004, urging world leaders to recognize the link between public and environmental health. The SARS-CoV-2 spillover has rekindled the interest in One Health, but it is complex to integrate various disciplines into surveillance.
For example, in medicine, clinical diagnostics attract public and private funding, but the same does not hold for animal diagnostics. Therefore, cost-effective innovation is required to address this disparity between animal and human health. In the context of innovation, a recent modeling study identified 47 new bat reservoirs for beta-coronaviruses using machine learning, with a perspective that it could be applicable for surveilling other zoonotic viruses.
Surveillance and preparedness
The emergence of a novel strain of influenza has been a pandemic-level threat. Nevertheless, surveillance and preparations could be made by learning from past epidemics and with a multidisciplinary approach and innovation. All recent cases of H5 infections were in individuals directly in contact with birds; importantly, transmission among humans has not been detected. This threat can be seen coming, and the ‘One Health’ concept is essential to avert an influenza pandemic.