Still a Scourge
March of Dimes Birth Defects Foundation
In his classic A History of Poliomyelitis, Yale epidemiologist John R. Paul makes what has become a well-accepted case for the reason polio reached epidemic proportions during the late nineteenth and early twentieth centuries. Societies were once awash in poliovirus, Paul suggests, and children were exposed as infants, while still protected by maternal antibodies. But beginning in the 1800s, improvements in hygiene, water quality and sewer systems reduced that exposure. As more children failed to develop immunity, terrifying polio epidemics broke out in the United States and Europe.
But if those outbreaks resulted from improved hygiene, why does polio today occur in filthy, crowded locales with high birth rates, poor hygiene and bad water quality? According to Paul’s hypothesis, such conditions ought to leave infants exposed to poliovirus at a young, less vulnerable age. So how can polio be associated at once with dirt and cleanliness, with poor and good water systems?
One possibility could be the role of breastfeeding in providing immunity. The maternal antibodies in breast milk lend some protection against infection while it is in the gut, says Eckard Wimmer, a polio virologist at the State University of New York in Stony Brook. Breastfeeding diminishes the chance that the virus will leave a child’s intestines and invade the nervous system. Adults who have been infected with polio have high levels of antibodies, some of which will be passed on through the placenta and the milk of a nursing mother.
Before the nineteenth century, children may well have been exposed to constantly circulating poliovirus while still protected by maternal antibodies—both after birth and through breastfeeding, which often lasted two years or more. But exclusive breastfeeding rates dropped drastically during the late nineteenth and early twentieth centuries, bottoming out during the 1940s and ’50s in Western countries. The same thing happened in the developing world, and despite some recent improvement, rates remain low, according to Claire Hajaj of UNICEF. Though it’s difficult to prove a link between the decline in breastfeeding and the rise of epidemic polio—and the virus’s continued presence in countries where breastfeeding is rare—the timing and what we know about the disease suggest there could be some connection.
But whatever the cause of the outbreaks of epidemic polio in the first half of the twentieth century, it mystified physicians and petrified parents. Summer was an especially terrifying time: Swimming pools and even parks were off-limits, and many parents kept their children indoors and away from crowds; you never knew where, or how, the virus might strike. One of the most frightening aspects of polio was its stealth. Unlike smallpox, for example, which left its unmistakable mark on everyone it touched, polio infects as many as 1,000 people for every one who is felled by paralysis.