How do we know when an animal virus might pose a risk to humans? Canada confirmed a human case of H5N1 avian influenza (often called “bird flu”) in 2024, the first ever known to have been acquired in Canada. The patient, a thirteen-year-old British Columbian, suffered severe symptoms including respiratory failure but recovered with intensive care in hospital.

Uncovering insights into how pathogens can switch from animals to humans — as in this human case of bird flu — can help researchers and public health agencies prepare for future outbreaks. In a recent study, our lab examined viral mutations in this case and uncovered an unexpected result: the effects of these mutations were inconsistent with the usual warning signs we expect to see in a virus adapted to infect humans.

How we usually monitor influenza

Public health agencies and collaborating groups use complementary approaches to monitor infectious disease outbreaks and risk. Human outbreak data comes from many places, including care settings and associated surveillance labs, volunteers reporting disease status, and wastewater monitoring. Current routine virological tests in public health labs include sequencing viral genes, testing for antiviral resistance and assessing immunity against strains of interest.

Read more: Sewage surveillance: How scientists track and identify diseases like COVID-19 before they spread

From wildlife and agricultural monitoring, Canadian agencies have tracked the arrival of the currently dominant H5N1 lineage of avian influenza, of which the B.C. case is a member. In this case of a human H5N1 patient in B.C., sequencing efforts........

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