Polio - Past, Present and Post Polio Syndrome

Perhaps we'll start off with Anupam.

Perhaps for our listeners who have never seen a case, what is poliovirus, and how does it cause disease? Can you walk us through the journey from ingestion to paralysis and explain why it targets motor neurons specifically?

So poliovirus is an enterovirus.

It is essentially gut infection, a small RNA virus that spreads via the fecal-oral route, and it replicates in the gut and regional lymph nodes.

Now, in vast majority, in 90% cases, the infection is entirely asymptomatic.

Up to 10% can get a flu-like symptoms, and less than 1% of the people infected can get the effects of polio, what we are going to talk about, because in those patients-These viruses go-- reach the spinal cord via the bloodstream through the neural pathway, and they have this predilection for the anterior horn cells of the spinal cord.

And they destruct those anterior horn cells and, or ha- anterior horn cells are very important neural pathway known as lower motor neuron.

So when we get a lower motor neuron lesion, lower motor neuron starts from the anterior horn cell, then the roots, then the nerve, and then go to the muscles.

Anything from anterior horn cell downward is lower motor neuron lesion.

And when the lower motor neuron is affected, like in diabetes and other things, we get a, what we call flaccid paralysis, where muscles tend to become weak, flaccid, less tone, and we cannot elicit the reflexes.

And interestingly, this virus has the predilection for affecting certain areas of the spinal cord.

Like very common is the lumbar region of the spinal cord.

That is why they attack the anterior horn cells of the lumbar region.

That is why we get the weakness and paralysis of the leg muscles, because leg innervation starts from L1.

Similarly, they can affect the bulbar muscles when in the brain stem motor nuclei and can have a paralysis of diaphragm, respiratory complications, swallowings can get affected, which is a very serious complications.

So there are a couple of serotypes, poliovirus one, two, and three.

Poliovirus two has been eradicated.

Last poliovirus three was detected in two thousand and twelve, and poliovirus one is the only remaining of the strain.

So yes, that it is the virus's natural tendency to attack the nervous system, and that's how we get all the signs and symptoms and paralysis of the legs.

We get atrophy, we get shortening, and all those deformities, so on and so forth.

So is there a particular type of person who will get it? Is it more common in lower economic communities or-- Bruce, do you have any thoughts on this?

Um, so I think that the important point was about having maternal antibodies.

And so I think that when adults had been exposed, then they will have antibodies.

When the mothers then has the baby in the womb, there are maternal antibodies that are shared with the baby, and when the baby's then born and is exposed to poliovirus, they're already protected by maternal antibodies and then possibly develop their own antibodies.

So if subsequently they're exposed, then they have immunity.