Note: This column is for information purposes only and is not intended as a substitute for professional medical advice.

Q: I had polio in 1945 that affected my legs and one arm. The doctor told my mother I had spinal polio. But he also said I had two types of polio because I had caught two polioviruses. Do I have one type of polio or two?

A: It depends on what the definition of "types" is. There are three types of polioviruses, named originally for the location where they were found, either in a city or inside a person. Types are different because your immune system makes a different antibody for each. But they are also different in terms of how common they are and their ability to cause harm. Almost all of the polio epidemics were the result of Brunhilde Type I poliovirus, which caused leg, arm and sometimes breathing muscle paralysis. The Lansing Type II virus seems to have been least likely to cause paralysis but could damage the so-called "bulb" of the brain--the brain stem that lies just above the spinal cord--and was apparently responsible for huge outbreaks of nonparalytic polio. Leon Type III poliovirus was the most rare, caused leg and arm paralysis, but also severely damaged the brain stem. All three poliovirus types could damage both brain and spinal cord neurons.

Since only one type of poliovirus had been identified in 1945, your doctor couldn't have known you'd had two types. It is most likely that you were infected only with Type I. Some polio survivors were attacked by two types at the same time, while a very unlucky few were attacked by one type in one year and a different one later in life because antibodies to one type didn't protect against the others.

Even though there are only three types of poliovirus, there are as many as 100 variations on the types, called "strains." The existence of many strains has nothing to do with antibodies, but has everything to do with virulence--differing abilities of strains to multiply in your body, to get inside your neurons and to damage them. The fact that some strains do no damage at all allowed Albert Sabin to develop a vaccine containing all three types of live poliovirus using strains that are non-virulent--that is, able to cause your body to produce antibodies but unable to hurt neurons.

To make things more confusing, there is another way to type polio: according to symptoms. Polio survivors who had severe damage to the brain stem were diagnosed as having bulbar polio. Although the numbers vary from year to year, up to 15 percent of patients were bulbar. And it was bulbar damage with its triad of symptoms that made polio a killer. Damage to brain stem breathing neurons prevented the diaphragm from moving in about one third of polio patients; some who had trouble breathing needed the iron lung, and about 70 percent of those died. Just over 50 percent with bulbar polio had trouble swallowing, 5 percent of whom died. Almost 10 percent had trouble controlling their heart rate and blood pressure, over 80 percent of whom died. Overall, about one third of those diagnosed with bulbar polio didn't make it.

Most patients had spinal polio, meaning the poliovirus severely damaged the motor neurons in the spinal cord, causing arm and leg muscle weakness and paralysis. Bulbar/spinal polio was diagnosed when patients had symptoms of both types. However, it was known in the 1950s that polio survivors had to lose 60 percent of their spinal cord motor neurons to have any muscle weakness, let alone paralysis. So polio survivors diagnosed as having non-paralytic polio could actually have had spinal polio and not known it. What's more, every polio survivor had some damage to brain stem neurons, damage that today is implicated as the cause of post-polio brain fatigue, muscle twitching and difficulty breathing during sleep, as well as trouble swallowing (see Post-Polio Forums for January and May 2002). So in terms of PPS symptoms today, former bulbar patients can have arm and leg weakness, spinal patients can have evidence of bulbar damage, and non-paralytic polio survivors can have evidence of both types.

What type of polio did you have? Nasty. That's what the poliovirus is.