Poliovirus

General:

Poliovirus is a single-stranded, positive-sense RNA enterovirus (genus) of the picornaviridae family.
There are three poliovirus serotypes (P1, P2, and P3).
Incubation period is approximately 7-10 days
Poliovirus can cause serious damage e.g. if it spreads to the CNS it can result in paralysis
Transmission of poliovirus is faecal-oral
Disease it causes is poliomyelitis
- Death of the motor neurons in the spinal cord, thus bringing about paralysis
Replication:
- Poliovirus typically replicates in the oropharyngeal tonsils and the Peyer's patches (small masses of lymphatic tissue) of the ileum.
- This causes viraemia which can then causes infection of the anterior horns of the spinal cord, which house the motor neurons of the spinal cord
- Following this, infection of the meninges (leading to meningitis) or the brain (leading to encephalitis and paralysis in <1% of cases) can occur
Epidemiology:
- Mainly still affects areas of Afghanistan and Pakistan (especially the mountainous regions)

Vaccination:

Salk Vaccine:
- Introduced in 1955 containing poliovirus strains from each of the three serotypes that have all been inactivated using formalin.
- Intramuscular administration
- Generally given in 5 doses as part of the NHS vaccination schedule (4 between 8 weeks and 3 yrs 4 months and a booster at age 14)
Sabin Vaccine:
- Introduced in 1961, containing low-virulence live attenuated strains of each of the three serotypes.
  - Monovalent (one serotype only)and bivalent vaccines of this type are also available for certain areas with high incidence of one poliovirus serotype.
- Oral administration
- More generally used for mass immunisation campaigns in low-income countries
- Three doses generally for immunity but in some areas up to seven can be given
- Vaccine Derived Polio Virus (VDPV) occurs in areas of low vaccine coverage, as the OPV strain(s) acquire the virulence and transmissibility of the wild type strain by genetic drift thus leading to outbreaks of infection.
  - These VDPVs are mainly found in African countries and are now a larger problem than the wild type strain itself (e.g. war in DRC meant that healthcare workers couldn't get into the country to give the vaccine, thus leading to a large outbreak)
  - Most cases of VDPVs are due to the P2 serotype of poliovirus
  - In OPV Type III, a single point mutation at nucleotide 472 causing a uracil to become a cytosine is associated with the development of VAPP.
Global Polio Eradication Initiative (GPEI):
- Uses oral Polio vaccine combined with one dose of intramuscular polio vaccine (to reduce VDPVs)
- GPEI Polio Endgame Strategy 2019-2023 aims to eradicate the condition entirely by the end of 2023

	Created by Matthew Coulson over 4 years ago

Sheila says that if there was to be a question regarding this in the exams it would almost definitely be about norovirus/rotavirus pathogenesis or the polio global eradication