Polio is caused by one of three wild-type polio viruses.
Of course, anti-vaccine folks like to push misinformation about polio being caused by a lot of other things, from poor hygiene and eating too much white bread to having a tonsillectomy or being exposed to pesticides, like DDT.
“Williams describes the many blind alleys and false leads of the early days of polio research, when doctors, scientists, and public health officials were convinced that the disease was transmitted by bedbugs, budgies, cats, and flies, or caused by seafood, cow’s milk, jimson weed, fruit, vegetables, and DDT…”
If the polio virus doesn’t cause polio (germ theory denialism), then you can’t really expect the polio vaccine to prevent polio, now can you?
The DDT-Polio Connection?
There actually is a bit of a connection between polio and DDT, but not the one anti-vax folks think.
No, DDT didn’t cause polio.
“Between the end of World War II and the early 1950s, researchers, municipal officials, and individuals from Georgia to California employed DDT to stop polio by killing flies, a suspected but debated actor in the disease’s transmission.”
Conis on Polio, DDT, and Disease Risk in the United States after World War II
Yes, many towns would routinely spray with DDT after a polio epidemic came to town because they didn’t yet know what did cause polio.
For example, in May 1946, “sections of the city were blanketed” with DDT as they sought to stop the source of a polio epidemic in San Antonio, which they thought might be a “tropical mosquito.”
See the connection now?
Polio first. DDT spraying after.
This idea is especially easy to see when you understand that there were many polio outbreaks and epidemics in the late 19th and early 20th century, well before DDT was discovered to be an effective insecticide in the early 1940s.
And the spraying mostly stopped before the polio outbreaks stopped.
In 1951, although he wasn’t yet sure how the polio virus spread, Dr. Sabin did know it came from “human feces derived from patients and healthy carriers,” and he declared that there was “general agreement that there is no justification for initiating emergency insect control measures in the hope of stopping a poliomyelitis epidemic.”
“It is perhaps an established epidemiological principle that epidemiological probability must be compatible with bacteriologic (or virologic) possibility, particularly when the epidemiological probabilities lend themselves to several alternative explanations.”
Albert B Sabin, MD on Transmission of Poliomyelitis Virus
And even before that, the Editorial Board for the American Journal of Public Health, in 1946, said that “While municipal cleanliness and sanitation are always highly desirable, there is no reason to believe that improved methods of sewage treatment and disposal, more rigid standards for the purification of water supplies, or the dusting of DDT over a city from aeroplanes will have any measurable effect on the incidence of infantile paralysis.”
Also remember the other big reason that we saw DDT spraying in the United States – the elimination of malaria.
“The National Malaria Eradication Program, a cooperative undertaking by state and local health agencies of 13 southeastern states and the CDC, originally proposed by Louis Laval Williams, commenced operations on July 1, 1947. By the end of 1949, over 4,650,000 housespray applications had been made.”
CDC on Elimination of Malaria in the United States (1947 — 1951)
Did the spraying of DDT to eliminate the flies that transmit malaria in the southeastern United States correlate with extra cases of polio?
There were big outbreaks in New York, Indiana, Ohio, and many other parts of the country that didn’t spray DDT to help fight malaria.
“The peak year for use in the United States was 1959 when nearly 80 million pounds were applied. From that high point, usage declined steadily to about 13 million pounds in 1971, most of it applied to cotton.”
EPA on DDT Ban Takes Effect
Did we stop spraying with DDT in the early 1950s because it was banned and is that why we stopped seeing so much polio?
The peak year for DDT use was in 1959. Surprisingly, we don’t see that peak on any anti-vaccine graphs in 1959…
What was the peak year for polio cases? It wasn’t 1959 or 1960, as you would expect if there was a link between DDT and polio.
Although the use of DDT decreased after 1959, it was used until it was “banned” in 1972, and even then, there were exceptions for public health uses.
The polio virus causes polio.
Or at least why did we start seeing so many more cases in the late 18th through the mid 19th century, until it was controlled with our polio vaccines?
“…contrary to the prevailing “disease of development” hypothesis, our analyses demonstrate that polio’s historical expansion was straightforwardly explained by demographic trends rather than improvements in sanitation and hygiene…”
Martinez-Baker et all on Unraveling the Transmission Ecology of Polio
One rather simple and elegant explanation is that we started to get too clean, the “disease of development” hypothesis.
Improved hygiene and sanitation helped delay when kids would get polio. Remember, polio is spread by contaminated food and water through fecal-oral transmission.
So instead of routinely getting it when they were newborn babies or young infants, when they still had some protection from maternal antibodies, they got it later when they had no immunity. So polio essentially changed from an endemic disease, or something that everything got, to an epidemic form.