Why do we think we can completely eradicate polio?
Limited host range, fewer strains, effective vaccines
What is polio?
It could paralyze respiratory muscles
iron lung
It had disfiguring, crippling and sometimes fatal results.
most people exposed to polio virus are fine - asymptomatic infeciton
- ~90% of ppl won’t even know they’re infected
What are the vaccines used for polio?
Two vaccines for polio
- Salk and Sabin vaccines
salk vaccine is heat killed
- no chance of reversion
- what’s given to U.S. children
sabin vaccine is attenuated
- has occasional mutation from attenuated to wild type strain
All 3 serotypes (strains) of polio have to be included in the vaccine you receive
What kind of virus is polio?
“Entero” = intestine
- Transmitted by an oral-fecal route
Picornaviridae family
Small, (+) strand RNA viruses
Naked (non-enveloped)
- icosahedral capsid (made of 4 capsid proteins)
Over 70 distinct types of human enteroviruses
- 20 recognizable clinical syndromes
Go over the classification and general structure of polio?
Small virions, 30 nm in diameter
Icosahedral-shaped capsid
Nonenveloped
Acid-stable
able to withstand the GI tract
(+) ssRNA genome ~7441 nucleotides in length
Go over the specifics of poliovirus genome and structure
VP = virion proteins
4 VP’s make up the capsid of poliovirus
(+) strand RNA virus so after uncoating, the (+) send RNA strand begins translation
- translation into polyprotein (P1+P2+P3)
- P2+P3 make proteases which break apart sections of
- polyprotein into individual proteins for capsid
- also codes for polymerases
How does poliovirus enter?
Polioviruses attach to host cells via the poliovirus receptor (PVR or sometimes called CD155)
Binding causes a conformational change in the internal capsid proteins. VP1 is translocated to the surface of the virion and forms a pore in the cell membrane.
- ssRNA escapes into cell cytoplasm
The viral + ssRNA genome enters the cytoplasm
What are the steps of the poliovirus lifecycle?
- Attachment/Entry
- Uncoating
- Immediate production of viral proteins (polyprotein)
- Processing of polyprotein into individual virus proteins
- Negative sense (-) antigenome made fom + strand genome
- Positive (+) strand genomes generated from antigenomes
- More production of viral proteins
- Genomes packaged into pre-assembled capsids
- Virions released from the cell by cell lysis
Go over the poliovirus pathogenesis.
Transmitted via fecal/oral
- begins replication in small intestine
- then to draining lymph nodes
- replication
- primary viremia = in blood stram 1st time
- access to spleen, liver (target organs)
- further replication in target organs
- secondary major viremia
Most time host immune system (adaptive antibodies) prevents access to CNS (no paralyzation)
if immune resposne not quick enough the virus attaacks motor neurons = paralysis
How many serotypes of polio are there?
Three serotypes of polio (strains)
Go over the course of mild polio infection.
95% of all poliovirus infections are asymptomatic
Asymptomatic persons shed virus in stool and are able to transmit the virus to others
still infected, shedding and spreading virus
About 4-8% of poliovirus infections cause mild symptoms: Malaise Gastrointestinal distress Fever Sore throat
Complete recovery occurs within a week
Go over the course of moderate polio infection.
Aseptic meningitis (minor illness) followed by: Stiff neck/back, and/or legs
These symptoms last 2-10 days followed by a complete recovery.
Go over the course of major polio infection.
Occurs in less than 1% of all poliovirus infections
Flaccid paralysis—weakness
- one limb or other
Inflammation and destruction of motor neurons
- trouble operating limbs
What is the treatment for polio? Is there a cure?
The Polio era in the United States.
- Drinker respirators or iron lungs introduced in the 1930’s
Sister Kenny
- Physical therapy rather than immoblization of the affected muscles
- Hot packs and hot baths
There is no cure.
- Treatment is supportive care, including physical therapy.
- No antivirals available.
How is polio diagnosed in the lab?
Most common method: isolate virus from stool samples
Grows well in characterized in any human or monkey kidney cell lines (causes good CPEs)
Identify serotype with neutralization assays
Nucleic acid methods
The WHO is trying to eradicate polio. Why do they think this is possible?
Poliovirus eradication considered possible because:
- 2 vaccines available
- No animal reservoir
- 3 attenuated serotypes are stable
- OPV inexpensive and easy to administer in mass vaccination campaigns (National Immunization days)
What 4 components comprise the current strategy to eradicate poliovirus?
- Achievement and maintenance of high levels of routine immunization
- keep herd immunity high - Use of National Immunization Days
- delivery of vaccine to ALL children under 5 years of age in a very short period of time (1-3 days)
- leads to a rapid increase in herd immunity
- breaks the chain of transmission for poliovirus
- In India in 2004 more than 125 million children were vaccinated in a few days - Surveillance and rapid response to any cases of acute flaccid paralysis
- Use of “mopping-up” activities
- Strategy focuses on an area or country where the previous 3 components of the eradication program have successfully reduced the number of poliovirus cases to a small number
- the idea is to intensify immunizations in these areas to eliminate the last chains of transmission
What are the roadblocks to polio eradication?
Poliovirus is contagious—oral-fecal route, stable virus
Use of IPV in tropical regions is problematic
Some resistance to mass vaccination
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Introduction to Viruses23
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Viral Life Cycles16
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Viral Structure and Genome Replication21
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Viral Taxonomy4
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Viral Cultivation/Detection21
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Viral Pathogenesis92
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Immunity30
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Epidemiology24
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Gene Therapy10
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EHV-1 as an Oncolytic Vector17
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Oncogenic Viruses33
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Enteroviruses18
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Influenzaviruses37
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Pox viruses13
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Herpesviruses17
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Rabies21
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HIV/AIDS26
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Review32
