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Polio Eradication. Dr Marvin Hsiao Division of Medical Virology NHLS/UCT/Groote Schuur Hospital. The virus. Single strand positive sense RNA virus Non-enveloped Family Picornaviridae Genus Enterovirus 3 types, poliovirus 1-3 Grows well in cell culture. The pathogenesis.

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polio eradication

Polio Eradication

Dr Marvin Hsiao

Division of Medical Virology

NHLS/UCT/Groote Schuur Hospital

the virus
The virus
  • Single strand positive sense RNA virus
  • Non-enveloped
  • Family Picornaviridae
  • Genus Enterovirus
  • 3 types, poliovirus 1-3
  • Grows well in cell culture
the pathogenesis
The pathogenesis
  • Faecal oral transmission (+respiratory)
  • Replicate in the lymphoid tissue in throat and gut - Viraemia
  • Replication in neuronal cell – especially motor neuron in spinal cord (polios: grey muelos: marrow)
  • Lytic infection of neurons
    • Anterior horn cell
    • Axon degeneration
  • LMN (flaccid) paralysis
the disease
The disease

Adapted from Collier & Oxford Human Virology 2nd Edition

Poliovirus infection

asymptomatic

Mild Febrile Illness

Full recovery

Meningitic Stage

Post polio syndrome

Acute Flaccid Paralysis (+/-1%)

Death

the vaccines1
The vaccines

*VAPP = Vaccine associated paralytic poliomyelitis

the campaign
The campaign
  • 1988 World Health Assembly passed a resolution to eradicate polio by 2000
  • The Global Polio Eradication Initiative was founded – Biggest Public health initiative to date
  • Task: co-ordinate eradication of poliovirus globally and source funding
global status 1988
Global Status 1988

http://www.polioeradication.org/

350 000 cases polio-1988

125 polio-endemic countries

global status 2004
Global Status 2004

http://www.polioeradication.org

1,263 cases in 2004 (99% reduction in cases)

1000 childhood paralysis prevented per day

6 polio-endemic countries, 5 countries re-established transmission

the challenges
The challenges
  • Funding gap
  • Containing polio in endemic area
    • Nigeria
    • Uttar Pradesh and Bihar states in NE India
  • Containing polio epidemics due to importation (Namibia)
  • Vaccine derived polio viruses (VDPV)
  • Laboratory containment
polio endemic area
Polio endemic area
  • Nigeria
    • Overcoming political and religious resistence
    • Vaccination campaign back on track
  • India
    • High intensity of polio transmission combined with high incidence of enteric disease
    • Despite good coverage unable to interrupt transmission of polio
  • Monovalent vaccine (response to single dose mOPV is >75% compare to tOPV 25%)
the namibian experience
The Namibian experience
  • Prior to the outbreak
    • Started OPV 1990, coverage of 60-80%
    • Last case of polio reported 1996
    • AFP surveillance: 2.6/100,000 and 86% stool collection rate (adequate)
  • The outbreak:
    • Index case May 2006
    • 185 suspected cases
    • 20 laboratory confirmed cases
    • 21 deaths, ¾ are adult over 15 years
    • Gaps in immunisation – a number of susceptible adults
the namibian experience1
The Namibian experience
  • Virus identified as poliovirus type 1 SOAS genotype
  • Same strain as Angolan outbreak and NE states of India
  • Molecular distance compare to parental strain is approximately 2.5 year
  • Unclear whether imported from Angola or India
the namibian experience2
The Namibian experience
  • Massive immunisation campaign targeting the entire population.
  • Three national immunisation days.
  • > 2 million doses of monovalent OPV1 administered
  • Outbreak halted
the namibian experience3
The Namibian experience
  • Lessons learned:
    • Coverage needs to be >80% -Immunisation gap
    • Importance of disease surveillance
    • Traditional AFP surveillance on children <15 yo is inadequate marker of polio elimination
    • Importance of laboratory network and regional reference laboratory
    • Constant risk of importation
    • Political will – immunisation campaigns
vdpv vaccine derived polio virus
VDPV (Vaccine derived polio virus)

OPV genome

  • <1% VP1 genetic divergence = vaccine strain (Sabin-like virus)
  • 1-15% VP1 genetic divergence =
    • Vaccine derive polio virus (VDPV)
    • cVDPV (evidence of circulation in the communities)
    • iVDPV (chronically shed by immunocompromised individuals)
  • >15% VP1 genetic divergence = wild polio virus

99

85

the laboratory containment
The laboratory containment
  • A country cannot be certified as polio free unless all laboratories are free of poliovirus
  • If 1 country is not certified polio free, polio cannot be eradicated
  • Potential sources polio outbreak:
    • Stored stool specimen, past poliovirus isolates, polio vaccine manufacturing facility
    • Past enteric pathogen research specimen
    • Past environmental surveillance (water) samples
    • Past respiratory specimen (routine/research)
    • The “mystery” vial / Legacy of previous research in the –70 freezer
is it possible to eradicate polio
Is it possible to eradicate polio?
  • It is possible and it has to be done
  • Prevent re-emergence of polio we need to:
    • Keep vaccinating with routine EPI and various campaigns
    • Good acute flaccid paralysis surveillance
    • Rid the laboratory of wild and vaccine poliovirus
    • Stop using OPV in the final phase of polio eradication
  • Thank you