7: Polio Flashcards
structure of poliovirus
RNA virus with no envelope but symmetric icosahedral structure
- no envelope means it survives better outside of host cell
tight protein-protein interactions so can survive without envelope
what is an envelope?
lipid membrane/bi-layer
- provides less immunogenicity
polio transmission
enterovirus because it infects gastrointestinal tract (GI)
replicates and comes out of GI tract
- mostly about contaminated water but still so infectious that even if you have good sanitation, it can be a problem
many infected are asymptomatic but can still spread the virus
end point of the polio vaccine
prevent paralysis
polio history
isolated/identified in 1908
first virus cultured in cells
- early vaccine development focused on polio/smallpox
infection and disease
virus spreads through the body and infects motor neurons
- not evolutionarily useful for polio since there is no transmission from a neuron cell to another person
broad ability to infect a lot of cells
- can infect neurons that control breathing
paralysis as a small percentage
- permanent paralysis if it kills motor cells
seasonality of poliovirus infections
seasonal with warm weather and/or humidity
high asymptomatic rate so difficult to assess if the virus is persistent over winter or reintroduced every summer
why did we have fewer paralysis cases before the 1900s?
age of infection changed with sanitation
- sanitation became municipal sanitation
polio infections occurred later in life when maternal antibodies were not present
- older children couldn’t control polio as well
- kids used to be infected young when they had antibodies from their mother (much more asymptomatic)
success of polio as a pathogen
highly contagious (up to 100%)
high number of asymptomatic infections which made it more successful
no treatment
only prevention to avoid contact/vaccine to prevent disease
polio salk vaccine
inactivated virus
- killed virus with no replication
- IPV
polio sabin vaccine
live virus
- replicate at any time
- attenuated but a lot slower
- OPV
similarities of 2 polio vaccines
trivalent with three wild type polioviruses
remarkably successful
vaccine success (reduction in paralytic polio)
IPV first used in 1955 and was a big success
- then switch to OPV in 1961 because it was easier and cheaper
OPV as a world standard for polio elimination
IPV as an inactivated vaccine did not provide long-term immunity and needed boosters
low cost of OPV because sabin gave the rights to WHO
given in liquid drops/sugar cubes so easy to administer
OPV and reversion of virulence
OPV can mutate when it replicates and revert to a virulent form known as vaccine-derived poliovirus (VDPV) that transmits to unvaccinated individuals
always a lot of unvaccinated individuals from baby births
OPV now no longer used in countries that eradicated polio
