Lecture 15

Question 1

what is poliovirus?

Answer 1

• an enterovirus
• member of the picornavirus family
• three serotypes (classification): type 1, 2, 3

Question 2

What is the pathway of the poliovirus once injested by a host, through the blood?

Answer 2

Day 0: virus injested

day 0-3: gut associated lymphoid tissue (ex. tonsils, peyer’s patches) becomes invaded by the virus. The virus replicates in the monocytes

Day 3-5: Regional lymph nodes become invaded, and the virus replicates in the monocytes (blood cells)

Day 5-15: Blood becomes invaded, which results in the virus in the blood of the host. Plasma viremia occurs here (this is when a virus is detected in the blood and is a good marker for tracking infection progression)

Day 8-12: Virus infiltrates the blood brain barrier and corsses the endothelium.

Day 10-30: Spinal cord becomes infiltrated. Virus replicates in the anterior horn cells, cell destruction occurs, paralysis can occur.

Day 5-45: Virus ends up in the gut, and is excreted in the feces

Question 3

why is it signifigant that the poliovirus is an enterovirus?

Answer 3

means that it is able to handle the low pH of the gut

Question 4

What allows for polioviruses to circulate unnoticed in a host?

Answer 4

can cause inapparent infections (ex. no symptoms till later on) which allows poliovirus the ability to circulate unnoticed

Question 5

When does the likelihood of developing paralytic polio increase?

Answer 5

increases with age. also the extent of the paralysis increases with age

Question 6

With paralytic polio does the entire body become paralyzed?

Answer 6

• in children, under the age of 5, paralysis of one leg is most common
• in adult, extensive paralysis of the chest and abdomen also affecting all four limbs is more likely

Question 7

How does spinal polio, the most common form of paralytic poliomyelitis, occur?

Answer 7

• results from viral invasion of the motor neurons of the anterior horn cells, or the ventral (front) grey matter section in the spinal column (which are responsible for movement of the muscles)
• virus infection results in inflammation, leading to damage or destruction of motor neuron ganglia
• this ends up leading to muscle atrophy and paralysis

Question 8

what is inactivated poliovirus vaccine (IPV)?

Answer 8

• chemically inactivated wildtype poliovirus
• injected vaccine
• there is no vaccine associated disease
• provides protective systemic immnity
• the antibodies produced by this vaccine can neutralize the poliovirus in the blood, and has the ability to prevent paralytic poliovirus.

Negative “Features”:
* provides limited mucosal immunity
* more expensive than OPV
* does not prevent transmission of poliovirus
* Does not prevent the poliovirus from being replicated in shed in the gut though.

Question 9

What is oral poliovirus vaccine (OPV)?

Answer 9

• it is a live attenuated poliovirus (slightly active, so has the ability to replicate in the gut)
• oral administration
• inexpensive
• provides systemic and muscosal immunity
• it provides the ability to get the antibodies into the blood and up the muscosal cells which then prevents the virus from having the ability to replicate in the gut and shuts down the ability of infected host cells to release/shed the virus.

Question 10

what is the major possible consequence associated with oral poliovirus vaccine (OPV)?

Answer 10

vaccine associated paralytic poliomyeltitis can (VAPP) occur

Question 11

What is Vaccine Associated Paralytic Poliomyelitis (VAPP)?

Answer 11

• when the OPV vaccine administred can actually be “turned against” the body
• RNA polymerases of the poliovirus can introduce mutations into the attenuated live vaccine virus, which can cause it to become viral again, and cause further infection.
• results in the shedding of revertant poliovirus

Question 12

Where do OPV recipients that have VAPP shed revertant viruses?

Answer 12

in the feces

Question 13

what are the rna sequence mutations that result in VAPP fromt the attentuated (vaccine) virus?

Answer 13

two mutations switch from a C to a U nucleotide base, and one U gets swapped with a C.

so overall there are 3 mutatiions that cause VAPP to occur, causing the attentuated virus to revert back to wildtype, causing further infection.

Question 14

who does polioviris infect?

Answer 14

only infects humans, no non-human reservoirs

Question 15

how long can poliovirus survive outside of a human host?

Answer 15

days-weeks

Question 16

how does the OPV vaccine block transmission of the poliovirus?

Answer 16

mucosal immunity from OPV vaccine blocks poliovirus transmission (where IPV does not)

Question 17

are there long term carriers of poliovirus?

Answer 17

no

Question 18

If we vaccinate enough people, will poliovirus dissappear from the environment?

Answer 18

the answer is thought to be yes. due to the following reasons:
* can only live in a human host, outside of a human host it has a short lifespan to actually live
* OPV vaccine provides hosts with the ability to block transmission due to its mucosal immunity
* and there are no long term carriers of poliovirus

Question 19

What are the problems that can occur when wildtype poliovirus has been eradicated?

Answer 19

• we would most likely stop poliovirus vaccinations. this would then result in a cohort of susceptible infants to poliovirus emerging.
• and since OPV is a vaccine containing live-attentuated poliovirus, this could pose a problem (especially since it can also cause VAPP)

Question 20

Why is it dangerous to stop poliovirus vaccinations even if poliovirus is eradicated from the environment?

Answer 20

• if there is an accidental release from vaccine production facilities of poliovirus since they must use live attenuated viruses for the vaccine, it is even more dangerous for society as the general population will be highly susceptible to infection