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A Devastating Disease: Polio

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1 A Devastating Disease: Polio
By Deshae Gehr

2 The Poliovirus Causes disease Poliomylitis, literally meaning “gray spinal cord inflammation It is a virus There are three types of poliovirus and many strains of each type It is contagious: usually spread from person to person. Only harmful to humans

3 What is a virus? A pathogen that is not actually living (debated)
Depends on a host cell to live Contains genetic material (RNA) enclosed by a capsid that protects the viral genetic material until it cann find a host Inserts genetic material into host cells, and uses cell to manufacture more viruses. Destroys cell when new viruses burst out

4 Lytic vs. Lysogenic Lytic:
When a dormant virus is stimulated and it begins to use the cell to manufacture new viruses, ultimately killing it. Lysogenic: When viruses remain dormant inside host cells for a period of time

5 Overview: Poliomylitis is caused by the poliovirus which belongs to the genus Enterovirus. They contain RNA, and target the gastrointestinal tract Structure: it is a single RNA genome enclosed in a protein shell (capsid). There are 3 groups of polioviris: Poliovirus type 1, 2, and 3 Each has a slightly different capsid protein PV1 is the most common, and most closely associated with paralysis

6 Polio 4 different kinds: Spinal, bulbar,bulbospinal, paralytic
All can result in paralysis of different parts of the body Poliovirus spreads along certain nerve fiber pathways destroying motor neurons within the spinal cord, brain stem, or motor cortex. This leads to the development of paralytic poliomyelitis in certain parts of the body, depending on where the central nervous system is damaged, Inflammation associated with nerve cell destruction often alters the color and appearance of the gray matter in the spinal column causing it to appear reddish and swollen The likelihood of developing paralytic polio increases with age Severity of paralysis also increases Paralysis in children occurs in only 1 in 1000 cases. In adults, paralysis occurs in 1 in 75 cases (http://en.wikipedia.org/wiki/Poliomyelitis#Cause)

7 Early Symptoms: high fever Headache Stiffness (back and neck)
weakness of various muscles sensitivity to touch difficulty swallowing muscle pain loss of reflexes Irritability Constipation difficulty urinating Paralysis develops 1-10 days after early symptoms begin Usually continues for 2-3 days, and complete soon after

8 How polio enters the body:
The virus enters through the mouth It multiplies in the throat and gastrointestinal tract It gets into the bloodstream and is carried to the central nervous system It replicates there It attacks motor neuron cells, ultimately killing them. (Motor neurons control muscles for swallowing, circulation, respiration, and the trunk, arms, and legs)

9 Attaching to the cells:
Human nerve cells have a protruding protein structure on their surface The polio virus comes in contact with the nerve cells, the protruding proteins act as receptors and attach to the cell The virus injects its genetic material (RNA) into the cell, causing the cell to become an assembly line for manufacturing new viruses. (see slide on how viruses work) The polio virus usually enters the lytic cycle

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11 1. Polio virus approaches nerve cells vai bloodstream
2. nerve cell receptors attach to virus. 3. viral capsid breaks to release RNA. 4/5.RNA takes over ribosomes: cell’s protein assembly, to make more viruses. 6/7. Newly manufactured viruses burst out of cell (killing it) and they move on to new nerve cells

12 Polio: Transmission Polio is highly contagious
Spread from human contact Transmitted in fecal-oral manner (generally occurs when food or water is contaminated), or oral to oral manner Its incubation period is anywhere from 3 to 35 days Most contagious 7-10 days before, and 7-10 days after

13 Polio: Transmission It was very prevalent among children, although anyone can get it, especially those with compromised immune systems Climate has been known to affect the transmission Temperate climates: with this climate the transmission peak for polio is in the summer and fall. However, with tropical climates the seasonal gap is not as noticable

14 Treatment: There is no cure for polio
Treatment is lessening severity of the symptoms (of weakness, paralysis) Some examples: antibiotics to prevent infections in weakened muscles Pain-relieving drugs moderate exercise and a nutritious diet Long-term rehabilitation; physical therapy Braces (body) Corrective shoes Orthopedic surgery Iron lungs (portable ventilators)

15 The Vaccine: Now there is a vaccine developed in 1952 by Jonas Salk
Albert Sabin later developed an oral polio vaccine Vaccines work by exposing the person to the virus in a controlled fashion so the body creates antibodies, that result in immunity.

16 Polio: History Polio is a disease that has existed since Egyptian times or before The 1st known clinical description is reported in 1780 by English physician, Michael Underwood 1st seen as a distinct condition in 1840 by Jakob Heine. Jakob Heine

17 Polio: History Polio was a devastating disease in the 20th century, particularly in the United States and Europe. Populations exposed to poor sanitation had become immune to the virus over time However, developing countries were increasingly getting better sanitation The natural immunity built up due to constant exposure made the general population more at risk (esp. 6 month-olds to 4 year-olds)

18 Polio: History Polio infections rapidly increased in new age countries beginning in 1900. The rate of death and paralysis from polio also increased drastically 1952: United States, had the worst epidemic in the nation's history. 58,000 reported cases: 3,145 died; 21,269 were left with mild to disabling paralysis

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