Thread by @lex6m

But what about #polio?
Polio is a nickname for poliomyelitis, which means inflammation of the grey matter of the spinal cord.
If you get a lesion on your spinal cord, that part of your body may develop paralysis.

This disease nearly always occurred in children, which is why it was called infantile paralysis for decades.
Polio was basically non-existent before the 1800’s.
You don’t really see it in medical literature until the 1890’s when it began to appear in epidemic form.

As it turns out, the paralysis of poliomyelitis can be caused by many different things.
Several viruses can cause it, as can several different bacterial infections.
Surprisingly pesticides could also cause it.

Studies were conducted in the late 1800’s with a popular pesticide called Paris Green.
They purposely fed animals too much pesticide and it paralysed them in their “hind quarters” just like what was happening with children.

Scientists did autopsies on the animals, found lesions in their spinal cords, and pronounced they had died from polio-from pesticide poisoning.
The pesticide contained a metal called arsenic, and may explain why parents originally referred to polio as teething paralysis.

A popular medical treatment at the time was “teething powders”, a concoction given to infants who were teething.
They contained massive amounts of similar metal - mercury.

Teething powders became popular in the early 1800’s and appeared about the same time you started seeing isolated cases of polio.
It became clear that certain viruses and bacteria could also cause paralysis, but only if they got inside the nervous system.

For all of human history, these microbes had never caused problems, but starting in the late 1800’s, they suddenly gained the ability to get into the nervous system.
This likely had something to do with a new pesticide that was invented in 1892 - lead arsenate.

It was a combination of lead and arsenic sprinkled and sprayed onto many fruits and vegetables that were later eaten.

It’s popularity was due to the fact it couldn’t easily be washed off with water - an advantage for farmers who didn’t have to re-spray after a storm, but a disadvantage for mothers trying to clean their children’s food.

It appears that not only did this metallic pesticide create paralysis through direct poisoning, but caused a leaky gut issue in children that allowed different viruses and bacteria to pass through the intestines and into the spinal cord directly behind.

Humans had lived with these viruses and bacterial infections for hundreds of years with no paralysis until the late 1800’s.
Within a year or two of the invention of this new pesticide, polio began to appear in that same area of the country.

In the 1940’s, at the end of WW2, a new pesticide called DDT began being used by nearly everyone and polio became much worse.
Unlike lead arsenate which was sprayed onto food, DDT was sprayed directly onto children in an attempt to protect them from flies and mosquitoes.

Ironically, it was thought that these insects could transmit polio, and DDT was sprayed onto children to prevent polio.
By 1952 people began to stop using DDT because many insects had already started to develop a resistance to it.

Parents also began to suspect it was more toxic than they had been told.
At the same time, cases of infantile paralysis, or polio, began to plummet.

1952 was the peak for polio cases in the United States - not just the kind caused by poliovirus, but the paralysis due to all other viruses, bacteria and direct pesticide poisoning.
They all began to disappear as DDT stopped being sprayed on nearly everything.

Even though all types of infantile paralysis began to go away after 1952, most history books will say it’s because of the Salk polio vaccine.
This is not true.
The vaccine worked very poorly, and the majority of the public didn’t even get it until years later.

It was officially introduced in 1955, but was quickly withdrawn because it was inadvertently causing paralysis due to manufacturing problems.

Many didn’t get a polio vaccine until years later, when a different, presumably safer version of the polio vaccine, the Sabin oral polio vaccine, came out in 1961.
By then polio had all but disappeared from the United States.
As it turns out, even the new vaccine wasn’t needed.

Polio had nearly vanished by then.
It had appeared suddenly in the 1890’s alongside the introduction of the pesticide, lead arsenate, and had suddenly disappeared in the early 1950’s alongside the abandonment of the use of DDT...