How is the disease transmitted?
Transmission occurs most often through contact with stool from an infected person eg. when food and water becomes contaminated. Less frequently, polio transmission can occur through contact with respiratory secretions or saliva. There is also evidence that flies can passively transfer poliovirus from faeces to food. The virus enters the body through the mouth and multiplies in the intestine. It is then released into the environment through faeces where it can spread rapidly through a community, especially in environments of poor hygiene and sanitation. Most people infected with the poliovirus have no signs of illness and are not aware that they have been infected. These symptomless people can carry the virus in their intestines and spread the infection to thousands of others until the first case of polio paralysis shows.
How the disease was perceived to be transmitted in the past
For most of history, poliomyelitis was a relatively unremarkable disease since it caused paralysis and occasionally death in a tiny fraction of those infected. This all changed in the early 1900s, when the disease transformed into an epidemic, killing many and crippling many more. In 1916, New York experienced a major epidemic of polio. Since the theory that Polio could be present in people without severe symptoms had not been developed yet, attempts at quarantining affected individuals had no effect. This heightened concerns about the disease and accelerated research into how the disease was spread.
Charles Caverly, MD, in 1894 was one of the first physicians to recognize that polio could occur with or without paralysis. However, Mr Caverly did not assume that the disease could be spread from person to person. In a book written by Charles Caverly called Infantile Paralysis in Vermont:
"The element of contagium does not enter into the etiology either. I find but a single instance in which more than one member of a family had the disease, and as it usually occurred in families of more than one child and as no efforts were made at isolation, it is very certain that it was non-contagious.” - Caverly stated.
However,after a series of polio epidemics in Sweden, Ivar Wickman (1872-1914) published two important findings about polio in 1905. First, Wickman suggested that polio was a contagious disease that could be spread from person to person. Second, Wickman also recognized that polio could be present in people who did not appear to have a severe form of the disease.
Health officials enforced the rules of sanitation in an attempt to control the disease, which they would later find out had actually worsened the spread of polio. Health professionals advised against open drains and unscreened windows. Parents were told to keep their children clean, well rested, well fed, and away from crowds. Nobody went to the public pools. When polio attacked, the cinemas were shut, camps and schools were closed, drinking fountains were abandoned and nonessential meetings were postponed until the epidemic seemed to be over for the time being. In the past, these types of precautions showed to be very effective in stopping the spread of deadly diseases such as influenza which is why people thought it could do the same with polio. However, these precautions were not helpful.
The reasons these sanitary improvements worsened polio was because it disrupted the natural immunity. In babies, polio can be mistaken for a mild cold because they still have protective antibodies left over from their mothers. That early exposure was enough to make the infant immune to that particular serotype of the disease for the rest of the infant's life. Polio is spread through a fecal-oral contact route, and most often through contaminated water. The adoption of modern plumbing, sewer systems and water treatment facilities in the late 1800s and early 1900s meant that infants were far less likely to be exposed to polio during the early ‘safe’ phase. Without that immunity gained in infancy, a chance of infection later in life could be deadly.
Finally, in 1908, Karl Landsteiner, MD (1868-1943), and Erwin Popper, MD (1879-1955), announced and confirmed that the infectious agent in polio was a virus. Popper and Landsteiner came to discover that polio was a viral disease by carefully filtering and examining the spinal cord fluid from a person who had died of polio. They filtered the fluid with filters that were known to trap bacteria. When Popper and Landsteiner injected the filtered preparations into monkeys, the monkeys also developed polio. The researchers then concluded that an infectious particle smaller than bacteria caused the disease.
Poliovirus itself would not be visible to researchers until the 1950s, when the electron microscope became available. In 1948, John Enders, Thomas Weller, and Frederick Robbins succeeded in growing poliovirus in live cells. This lead to Dr Jonas Salk creating the IPV vaccine which finally controlled Polio in 1955.
Charles Caverly, MD, in 1894 was one of the first physicians to recognize that polio could occur with or without paralysis. However, Mr Caverly did not assume that the disease could be spread from person to person. In a book written by Charles Caverly called Infantile Paralysis in Vermont:
"The element of contagium does not enter into the etiology either. I find but a single instance in which more than one member of a family had the disease, and as it usually occurred in families of more than one child and as no efforts were made at isolation, it is very certain that it was non-contagious.” - Caverly stated.
However,after a series of polio epidemics in Sweden, Ivar Wickman (1872-1914) published two important findings about polio in 1905. First, Wickman suggested that polio was a contagious disease that could be spread from person to person. Second, Wickman also recognized that polio could be present in people who did not appear to have a severe form of the disease.
Health officials enforced the rules of sanitation in an attempt to control the disease, which they would later find out had actually worsened the spread of polio. Health professionals advised against open drains and unscreened windows. Parents were told to keep their children clean, well rested, well fed, and away from crowds. Nobody went to the public pools. When polio attacked, the cinemas were shut, camps and schools were closed, drinking fountains were abandoned and nonessential meetings were postponed until the epidemic seemed to be over for the time being. In the past, these types of precautions showed to be very effective in stopping the spread of deadly diseases such as influenza which is why people thought it could do the same with polio. However, these precautions were not helpful.
The reasons these sanitary improvements worsened polio was because it disrupted the natural immunity. In babies, polio can be mistaken for a mild cold because they still have protective antibodies left over from their mothers. That early exposure was enough to make the infant immune to that particular serotype of the disease for the rest of the infant's life. Polio is spread through a fecal-oral contact route, and most often through contaminated water. The adoption of modern plumbing, sewer systems and water treatment facilities in the late 1800s and early 1900s meant that infants were far less likely to be exposed to polio during the early ‘safe’ phase. Without that immunity gained in infancy, a chance of infection later in life could be deadly.
Finally, in 1908, Karl Landsteiner, MD (1868-1943), and Erwin Popper, MD (1879-1955), announced and confirmed that the infectious agent in polio was a virus. Popper and Landsteiner came to discover that polio was a viral disease by carefully filtering and examining the spinal cord fluid from a person who had died of polio. They filtered the fluid with filters that were known to trap bacteria. When Popper and Landsteiner injected the filtered preparations into monkeys, the monkeys also developed polio. The researchers then concluded that an infectious particle smaller than bacteria caused the disease.
Poliovirus itself would not be visible to researchers until the 1950s, when the electron microscope became available. In 1948, John Enders, Thomas Weller, and Frederick Robbins succeeded in growing poliovirus in live cells. This lead to Dr Jonas Salk creating the IPV vaccine which finally controlled Polio in 1955.