‘A disease of better hygiene’

Polio, a disease of filth, has likely been with us for millennia.

But it only became a global plague when we began to clean up as the 20th century dawned.

“Polio is actually a disease of better hygiene,” says Dr. Allison McGeer, an infectious disease expert at Toronto’s Mount Sinai hospital.

The virus that causes it is found in human feces and raw sewage, and polio is known as a fecal-oral route disease. That means it’s passed on when stool particles on food or a hand are transmitted to other people and find their way into their mouths.

The vast majority of people who contract the polio virus, however, don’t end up getting the paralytic version of the disease, McGeer explains. For these people, the infection is confined, relatively benignly, to the gut. Yet these fortunate polio carriers still develop immunity to the disease.

And in less hygienic times almost everyone would have this immunity — and mothers could pass it on to their newborns.

“If you get infected with polio vi- ruses from raw sewage when you’re less than 6 months old, then you have you mother’s antibodies and you are protected from paralytic polio,” McGeer says.

“You develop a gut infection, you develop immunity in your gut, but you don’t get paralytic polio.”

The immunity the baby develops to the gut infection on their own, however, will remain with them for life.

“So the reason polio became such a problem in the 20th century is because we started having safe food and water for large segments of the population in the developed world,” McGeer says.

Cleanliness meant fewer mothers were able to pass on immunity to their babies. And those children did not develop a lifelong resistance themselves.

“In the 16th and 17th century, pretty much everybody would have been exposed to polio very early in life and would have developed immunity to it and would have been fine,” McGeer says.

“Mind you, they were exposed to lots of other things in the sewage that would have killed them in between.” —Joe Hall