Researchers at the Centre for Human Genetics and Pandemic Sciences Institute at the Nuffield Department of Medicine and colleagues from institutions including Borneo Medical and Health Research Centre, Universiti Malaysia Sabah and the Saw Swee Hock School of Public Health, National University of Singapore have developed a new surveillance approach for HPAI, encompassing analysis of both blood samples and spatial distribution of reservoir species.
Lead author Dr. Hannah Klim, Researcher NDM’s Pandemic Sciences Institute, said: ‘Our study highlights a previously understudied possible transmission route directly from migratory birds into humans. We hope this work will highlight the need to increase viral surveillance in migratory sites.’
To date, close contact with domesticated poultry – previously infected through contact with migratory birds – has been a widely discussed route of “bird flu” transmission into humans. While domesticated animals have been the focus of other studies, the new study, set in Malaysian Borneo, suggests that people living near habitats of these wild species may also have increased risks of exposure.
2,000 samples from individuals across four districts in Northern Sabah, Malaysian Borneo, were serologically tested for influenza exposure. The selected population was exposed to domesticated poultry and wild shorebirds, both potential carriers of H5 infection.
Analysis of blood samples identified antibodies suggesting that human participants had previously been exposed to H5 viruses. However, no human cases had ever been reported in the area – despite a severe poultry outbreak in 2018 and the presence of migratory birds known to carry H5 infection.
Corresponding author Kimberly Fornace, Associate Professor at Saw Swee Hock School of Public Health, National University of Singapore, said: ‘While all individuals in this study were healthy and there is no evidence of a current public health issue in this area, this study highlights how we can use environmental data and laboratory studies on past disease exposure to identify evidence of spillover and priorities for future monitoring.’
As a region experiencing both extensive environmental change and strong levels of avian migration, Malaysian Borneo is an important area for HPAI surveillance.
Climate change and the erosion of wild bird habitats may bring these species into much closer contact with domesticated species and humans alike – multiplying opportunities for zoonotic spillover events that see pathogens “jump” from animals to humans.
Not all study participants with the highest serological response owned poultry, but they all lived in proximity to migratory shorebird routes. This confirms the urgency of further research into pathogen transmission across species in migratory areas. Evidence from the study also seemed to exclude general influenza reactivity and cross-response from seasonal influenza infection or vaccination.
Confirmed cases of H5N1 in humans have been so far rare, but severe and with a high mortality rate. The study’s findings suggest that actual prevalence in humans may be currently underestimated – as non-severe cases may have been undetected or may have presented similar symptoms to other influenza types.
In the past few years, several H5N1 cases have been detected among livestock and wild animals globally – including a multi-state outbreak among dairy cows in the United States. Understanding actual rates of H5N1 exposure in humans will help prevent further spillover – and a possible new pandemic – as the virus may further mutate to maximise community transmission.
Read the full paper in Nature Communications: https://www.nature.com/articles/s41467-024-53058-y