The Real Story Behind the 1925 Nome Serum Run

On January 21, 1925, Dr. Curtis Welch put his head in his hands and did the math. Two children dead. Expired antitoxin that might as well have been tap water. A town of 1,400 people, most of them children, and diphtheria—the "strangling angel"—spreading through Nome like wildfire.

The good news: 300,000 units of antitoxin sat in Anchorage. The bad news: Anchorage was over 800 kilometers away, it was January in Alaska, and the harbor was frozen solid. No ships. Airplanes existed, sure, but antifreeze didn't. The mayor wanted to try anyway. Welch knew better.

That left one option, and if you've seen the 1995 animated movie Balto, you think you know this story. You don't.

What Diphtheria Actually Does

"Back in the early 1900s, diphtheria was, I think, around the fourth or sixth highest cause of death in the US with most of those deaths occurring in children under 5 years old," says Shawn True Love, an epidemiologist at Johns Hopkins who studies disease outbreaks.

The disease starts like a cold—runny nose, sore throat, nothing alarming. Then comes the membrane. Gray, leathery, foul-smelling tissue forms in the throat, made of cells killed by a toxin the bacteria secretes. Except the bacteria only secretes the toxin when it's infected with a virus. Diphtheria is so nasty even the bacteria causing it are sick.

This toxin—just called "DT" by scientists—doesn't just kill throat cells. It can damage the heart, nerves, kidneys. In 1921, four years before Nome's outbreak, the United States logged 200,000 cases and 15,000 deaths. Twenty percent of kids under five who got it died.

Welch had watched three-year-old Billy Barnett and seven-year-old Bessie Stanley die exactly this way. He tried the expired antitoxin on Bessie. It didn't work. Now he was staring down an outbreak with enough medicine for maybe six people.

A Town Built on Dogs

"The thing to understand about Nome at that time, and really a lot of northern places at that time, is that sled dogs, in the same way that our society now is built around cars, Nome at the time was built around sled dogs," says Blair Braverman, a long-distance musher who's raced the Iditarod.

Nome in 1925 wasn't the gold rush boomtown of 20,000 it had been in 1901. It was a sleepy outpost of 1,400 on the Seward Peninsula, 230 kilometers from the Arctic Circle. Wooden buildings, telephone wires, treeless tundra, and dogs everywhere. They went into bars with people. Everyone had their own team. They weren't beasts of burden—they were family.

And they were the only reliable link to the outside world. A thousand-kilometer dog sled trail connected Nome to the railroad town of Nenana, dotted with small settlements and rest houses. Twenty-five days to cross in winter. In summer, steamships could reach the harbor. One of those ships probably brought diphtheria to Nome in the first place.

When Welch sent his desperate telegraph, the US government scraped together 1.1 million units of antitoxin—enough for maybe 50 cases. But that would take time to assemble. The 300,000 units in Anchorage could save the kids dying now. Getting it to Nome meant dogs.

9,500 Years of Selection Pressure

Dog sledding isn't recent technology. In 1989, archaeologists on Zhokhov Island in Siberia uncovered domesticated dog remains 9,500 years old, alongside evidence of sleds and harnesses. These weren't pets. They were working partners, and their descendants are still working.

"When I started my PhD, I was doing the genetics of sled dogs and one of my questions was what is their ancestry?" says Heather Huson, who studies animal genetics at Cornell and grew up racing sled dogs. "The big thing that we found was sled dogs are their own breed."

They're not registered breeds like Siberian Huskies or Alaskan Malamutes—they're motley crews of different colors, coat lengths, ear shapes. But genetically, they're distinct. Selected for performance, not looks, over hundreds of years. Their DNA shows it.

One example: the amylase gene, which produces an enzyme that digests starch. Wolves have about two copies. Most dog breeds have up to 20 copies, evolved to handle agricultural diets. Arctic sled dogs? Seven to ten copies. They eat what their people eat—high meat protein. They've been shaped by the same environment, the same needs, the same impossible journeys across frozen landscapes where failure means death.

Modern sled dogs trace genetically back to those Zhokhov Island animals. The Thule culture brought them to Alaska about a thousand years ago, spreading across the Arctic with kayaks and dog sleds, eventually displacing the Dorset people. When the gold rush hit, demand for sled dogs exploded. Dogs were allegedly kidnapped from West Coast ports and shipped north. That genetic mixing created the working dogs of Nome.

The Dogs Who Actually Did It

Among Nome's mushers was Leonard Seppala, already famous for winning races with his lead dog Togo. They'd traveled 55,000 miles together. "The depth of understanding that he had with his dogs, the communication he was able to have with them," Braverman says, "was really unparalleled."

Balto was in Seppala's kennel too, but not his lead dog. And he definitely wasn't a wild wolf-dog living in a shipwreck with a Russian goose, despite what the movie suggested.

The real serum run wasn't one musher and one team making an impossible journey. It was a relay—multiple teams, multiple mushers, passing the antitoxin like a baton through blizzards and temperatures that could kill exposed skin in minutes. The video transcript cuts off before describing the actual run, but we know this: Balto got famous because his team made the final leg into Nome. Togo and Seppala covered the longest, most dangerous stretch. Both deserve the credit.

Balto died in 1933 and was taxidermied for the Cleveland Museum of Natural History. In 2023, scientists sequenced his DNA from tissue samples, confirming that genetic evidence of mixing—the scrappy, selected-for-performance ancestry that let him survive what he survived.

What We Don't Know Anymore

The antitoxin that saved Nome in 1925 worked by neutralizing the bacterial toxin—it didn't kill the bacteria or heal existing damage, just bought time for immune systems to catch up. It's made the same way now as it was then: inject horses with the toxin, harvest the antibodies from their blood.

Vaccines came a few years after the 1921 epidemic, but it's unclear how much reached Nome. Penicillin wasn't discovered until 1928. We have better tools now. We also don't think about diphtheria much anymore, which is why, as True Love noted, our understanding of the disease was "quite out of date" when he and colleagues reviewed the literature in 2020.

That's the double-edged sword of public health victories—we forget what we solved. Nome remembered. Those mushers remembered. The dogs remembered, in their way, in their DNA.

The real story isn't Balto alone. It's 9,500 years of evolutionary pressure creating animals capable of running through conditions that would kill most humans. It's mushers who knew their dogs well enough to ask for one more impossible thing. It's a doctor who made desperate calls because six doses wasn't enough. It's a disease so deadly we built an entire medical infrastructure to forget it existed.

And it's the fact that when everything else failed—ships, planes, trains—dogs got the job done.

—Nadia Marchetti