The Basic Biology and Transmission of Poliomyelitis
Figure 8: A Poliovirus Bound to a Neuron Receptor (10)
- Polio is a type of enterovirus from the family Picornaviridae.
- It is also known as poliovirus and poliomyeltis.
- Polio contains RNA and has three serotypes (P1, P2 and P3).
- Polio is stable in high pH (eg. Gastric acid) but is destroyed by heat, formaldehyde, chlorine, and ultraviolet light (11).
- Humans are the only known reservoir for polio (11).
Tab1: Wild polio enters the body through the mouth, typically by hands, food or water contaminated with fecal matter (12).
Figure 9 Poliovirus enters via the mouth (13)
Figure 10 Children can contract poliovirus by touching contaminated objects and putting their hands in their mouths (14)
Tab 2. Once inside the body, polio replicates itself in the pharynx and gastrointestinal tract (15).
Figure 11 The pharynx and gastrointestinal system (16)
It then travels into local lymphatic tissue and the bloodstream, where it may infect Central Nervous System (CNS) cells. In the event that polio infects CNS cells, it can then replicate in motor neurons in the anteriror horn and the brain stem.
The damage caused by this can result in nervous cell and tissue destruction, leading to the symptoms of paralysis in polio victims (17).
Figure 12 Cross-section of spinal cord displaying ventral (anterior) horn (18)
Tab 4. As polio remains present in the throat for approximately one week (19) and sheds itself in the feces of an infected individual, even in asymptomatic cases, disease can rapidly spread in areas with poor hygiene and sanitation. It spreads particularly quickly amongst young children who are not toilet trained (20). Polio can also be spread through an infected person's saliva (19) and there is evidence of passive transmission of the disease by flies (20).
Figure 13 Polio spreads in areas of poor sanitation, such as the community pictured above (21)
Figure 14: The Life Cycle of Poliovirus on a Cellular Level (10)
Video on Polio Transmission (video length: approximately 1:45)
RK: What a nice video from Smithsonian museum on how the poliovirus finds a host and starts the disease process. Looks like they have embedded this as a Flash activity. And they haven't given us access to the html code. Looks like we can't embed this, but we can link out to it. I wish you had given a little description of it so that people would be more apt to click it and view it. It's ok, don't worry. You have lots of good stuff in this module.
For further information, view the CDC Pinkbook chapter on Poliomyelitis: http://www.cdc.gov/vaccines/pubs/pinkbook/polio.html
Can Polio Save Lives?
New Research into the Therapeutic Use of Polio in Cancer
ABC News Segment on Duke University's efforts to treat brain tumors using polio. (1:10)
See More at: http://www.youtube.com/watch?v=KaJop2oti48