The Disease Detectives Trying to Keep the World Safe From Bird Flu

Dr. Luch berated herself for not having thought to test the boy a day earlier, when she might have saved him if she had treated him for influenza.

But the alarm she raised and the urgent activity that followed was testament to the strength of Cambodia’s disease tracking system and to its importance to the global biosurveillance system.

It is the fruit of years of international and local investment, training and public education. It shows how frontline work in low-income countries is increasingly vital to a global system to detect zoonotic diseases — pathogens that jump between animals and humans, the way Covid-19 did. The goal is to identify and contain them, buying time to produce enough vaccines or drugs to treat them, or to embark on a frantic mission to develop something new.

A growing threat

H5N1 is one of many viruses that cause influenza in birds. It emerged in Hong Kong in 1996 and has since evolved into versions that have caused outbreaks in wild and farmed birds and have occasionally jumped to humans.

In 2020, a new, especially deadly one caught the attention of scientists as it spread along migratory routes to parts of Africa, Asia and Europe.

By 2022, it had reached North and South America and was killing wild and domestic animals, including livestock and marine mammals.

So scientists were alarmed when, in February 2023, Cambodia reported two people who had been infected with H5N1. Was this the new version of the virus, returned to Asia and killing people? There had been no such human cases in the country for nearly a decade, though scientists had found that the virus had been present in birds all those years.

Genetic analysis established that the virus infecting Cambodians was the familiar subtype, not the one in the Americas — a relief. Still, in the past year, Cambodia has reported 11 people infected with bird flu, and five of them have died, more than anywhere in the world.

Global anxiety about H5N1 has risen higher in recent weeks, since the virus was detected in goats and dairy cows in the United States, and then in a Texas farmworker who fell ill.

As the virus moves between species, scientists fear the potential of the virus to evolve to spread easily not just from birds to mammals, but from person to person.