Is It Possible to Make Raw Milk Safe?

Top: From left to right, electron microscope images of the viruses that cause influenza, Covid-19, Ebola, Zika, and mpox. Visual: Undark; Base images NIH/NIAID

I n March 2013, a 27-year-old man showed up at the Fifth People’s Hospital in Shanghai, China, with a high fever and cough. Within 48 hours, he was admitted to the intensive care unit with severe shortness of breath. But no treatment could save him, and he died four days later. Chinese health experts later confirmed that the young man, who worked as a butcher, had been infected with an influenza virus called H7N9.

His wasn’t an isolated case. Other patients were trickling into Chinese hospitals with the same infection. Research later showed most of the infected individuals had a history of recent contact with poultry. But there were documented cases of patients infecting immediate family members who hadn’t recently been exposed to poultry, suggesting the virus might have been evolving a capacity to transmit among people.

Human cases of H7N9 flu appeared periodically in China and other countries over the next several years. Between early 2013 and late 2017, there were nearly 1,600 lab-confirmed cases and roughly 600 deaths. The infections sputtered out after Chinese officials launched a national campaign to vaccinate chickens against the virus in 2017. But on the other side of the world, at Pennsylvania State University, a virologist named Troy Sutton still had nagging concerns. Sutton was investigating how influenza evolves to become highly contagious, and he often worked with ferrets, which respond to flu viruses in much the same way as people. H7N9 should have struggled to transmit in ferrets, but Sutton’s research found that the virus could sometimes infect animals housed in adjacent cages, picking up new mutations along the way.

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