Recent questions on Internet polio lists have unmasked concern, among some, that they may now be affected with the post-polio syndrome (PPS) because their mother had polio while pregnant carrying them. Another worry, again expressed on Internet discussion lists, has been that the PPS is affecting the children of women who were pregnant while infected with polio because the virus damages the fetus during pregnancy. Concerns like these extend even to the mother, who has had polio in her history, although not during pregnancy, and now believes that her children are predisposed to develop post-polio syndrome. This has been imagined as a cause for the childrenís current perceived problems (back and leg related, for example) with an explanation served up by the motherís history of polio.
Letís look at the last concern first. There is no theory of PPS that could explain how someone who had polio in the past and later became pregnant could confer a predisposition to PPS to their offspring. The idea, in a way, reminds me of the disproved Lamarckian evolution theory, which attempted to explain why giraffes had long necks. The idea was that years of stretching to the high leaves elongated the giraffeís necks and after mating they passed on their long neck acquired trait to offspring. Today we know better. Traits are passed to children through the DNA of the parents. Acquired traits are not passed on.
Polio is a virus which infects, paralyzes, and is cleared by the immune system. Any stigmata, a weak leg for instance, is an acquired trait and cannot be passed to children. Amputees have normal children,and so do people who had polio. Poliovirus does its damage over a period of about 2 weeks by multiplying, damaging, and killing motor neurons inside the Central Nervous System (CNS). Then fever breaks, antibodies and the immune system prevail, and patients are no longer infectious, although they do excrete poliovirus for a month or so from the lymphatic tissue of the gut. Clearly, the titer and quality of excreted virus is below the infectious dose for passing a damaging infection to others. And the infected, not their children, must live with the acquired damage incurred to the CNS.
A brain-blood barrier protects the CNS, so even if one accepts an infective theory of PPS, that is, a theory where remaining mutant virus is activated within the spinal cord, blood separation would obviate any way to infect offspring. After a mother recovered from polio, she couldnít infect anyone else. And we donít know for sure if virus is what causes PPS.
Polio, we know, because of the meticulous studies of Sabin and Bodian in the 1940ís and 1950ís, enters into the body orally and exits in feces. It grows in the lymphatic tissue of the intestine and sometimes spills over into the blood causing a viremia (virus in blood). This situation can result in paralytic polio by virus migration through nerves into the CNS or by virus moving into the CNS through blood.
Figures 1 and 2 show a drawing of a woman carrying her fetus and a detailed cartoon of the placenta. The umbilical cord is attached to the placenta. Blood from the mother does not mix with blood from the fetus, so here we have a maternal blood/fetal blood barrier and the kinds of viruses which damage the fetus usually grow on or in the cord or on the membranes of the placenta. Such viruses as Rubella, or German measles, are the most commonly known. Other viruses, and there are a few, have a "tissue affinity" for the umbilical cord or the placenta, most likely because those tissues have receptors for the virus.
Blood circulates through the cord to the placenta, an organ with two layers of folded cells which separates blood of mother and child, the folds increase surface area between motherís blood and fetal blood, so antibodies, nutrients, oxygen, and other substances from the mother can dialyze through the two layers of placental cells to the fetus. Wastes from the fetus: carbon dioxide, urea, and various molecules dialyze across the placenta to the mother. Poliovirus, as will be shown below, does not grow in or dialyze through the placenta. This affords protection to the fetus.
There have been studies, during the polio epidemics of the last century, on the affect of polio infection in woman during pregnancy. One such study was done in Los Angeles and Illinois as described in a New Mobility article in April, 2001. In this study thousands of women in Los Angeles and Illinois had developed a polio infection while they were pregnant. Not one fetus showed ill effects due to the motherís polio.1 Other studies have shown that antibodies to polio move freely through the placenta while the polio virus does not. As pregnancy progresses the late fetus has more passive immunity than it had earlier during its fetal development. 2
A review of the literature on this subject demonstrated that although some fetuses could be found that had polio virus associated with them, the virus did not enter the Central Nervous System of the fetus and there was no paretic damage.3 It is likely that something went catastrophically wrong in such cases. Perhaps a damaged or malformed placenta was present or the mother was not immunocompetent.1
In the first 56 years of the past century when polio was epidemic, and add to that 3 years from the end of the 1800ís, there were 150 incidences of poliomyelitis reported in children who were under 6 months old.1 Included with these babies were 4 who were born with a limb paralyzed. So it is clear that contracting polio in the womb, through the placental barrier, is a miniscule risk. On the other hand, the same cannot be said about a mother who has polio.
Pregnant women who develop polio during pregnancy are 5 times more likely to die, although, consistent with the information above; the rate of miscarriage was no greater than that of a normal pregnancy.1
The Sabin oral polio vaccine confers active immunity by delivering 3 live polio strains, weakened, to grow in the gut of the vaccinated. There have been a number of studies that have demonstrated the safety of giving this live vaccine to pregnant women. 4 2 These data further bolster the observation that despite the lack of immune competence in an early fetus, live polio vaccine has not resulted in an infection or damage to a fetus.
Therefore, all of the scientific work done on this topic for over a hundred years, puts the idea that a polio infection, contracted in-utero could give rise to Post-Polio Syndrome, as so unlikely that to worry about this in retrospect is foolish. The question has been settled and may be safely set aside. Further, it would seem irrational to lay middle aged complaints, aches and pains, or even more serious medical problems, of those who never had polio, at the doorstep of PPS. This syndrome is a serious concern to those who have categorically been infected with polio and are seeking to have it more seriously addressed by medical systems around the world.
|Edward P. Bollenbach, BA, MA, Professor Emeritus in Biology, Northwestern Connecticut Community College, Winsted, Connecticut.
Known on most of the Internet post polio discussion lists simply as Eddie, he is a polio survivor who has a reputation as a clear and incisive thinker and a prolific writer.
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