1. POLIOMYELITIS & PRION DISEASE
Assist Prof
Dr. Syed Yousaf Kazmi

2. LEARNING OBJECTIVES
Discuss etiology, pathogenesis and epidemiology of poliomyelitis
Explain the role of immunization on epidemiology of poliomyelitis
List various prion diseases
Discuss etiology, pathogenesis and transmission of Prion disease
Discuss the role of sterilization & disinfection in transmission of prion disease

3. POLIOMYELITIS-ETIOLOGY
Poliovirus causes Poliomyelitis
Polio means “Grey”, Myelitis means “inflammation of spinal cord”
Belongs to genus Enterovirus, Family Picornavirus
Small (20–30 nm) nonenveloped
Three serotypes 1,2 & 3: all three serotypes can produce same disease
Serotype 1 severe disease

4. TRANSMISSION Fecal-oral route mainly Contaminated water or food
Poliovirus survives in sewage water at low temperatures
Multiplies in GIT of humans & passed in feces
For each reported case of paralytic polio, around 200 to 3,000 other contagious asymptomatic carriers exist
Humans are only natural host

5. EPIDEMIOLOGY
In 1988, there were 388,000 cases of paralytic polio worldwide
In 2005 there were fewer than 2000
1000 to 2000 cases each year
In 2012 cases decreased to 223
Nearing eradication-But extremely difficult
In three countries: Afghanistan, Nigeria, and Pakistan

6. POLIOMYELITIS-CURRENT STATUS

7. PATHOGENESIS
Poliovirus infection results in asymptomatic virus shredders in 95% while 4% minor illness
1 % cases –Aseptic meningitis or Paralytic polio
Incubation period 6-20 days
Healthy non-immunized person ingest virus
Virus multiplies in gut- lymphoid organs
Viremia-Virus reach CNS
Aseptic meningitis

8. PATHOGENESIS Risk factors for polio :
Virus multiplies in motor neurons mainly in anterior horn cells
Inflammatory cells cause death of motor neuron cells
Affected nerves-paralysis
Virus also affects brainstem-bulbar polio
Lifelong immunity after infection
IgA, IgG and IgM type antibodies
Risk factors for polio :
Immune deficiency, malnutrition, tonsillectomy, pregnancy

9. CLINICAL FEATURES Commonest presentation: asymptomatic (95%)
Non specific : headache, sore throat, nausea
Aseptic meningitis
Paralytic polio: Asymmetric flaccid paralysis
No sensory /cognitive loss
Muscle disuse atrophy
One leg/ one arm, or both legs/ both arms involved

10. ROLE OF IMMUNIZATION Two types of vaccines
Inactivated Polio vaccine (Salk)
Live attenuated vaccine (Sabin)
Contain three serotypes PV1, PV2 & PV3
Both vaccines induce humoral antibodies, which neutralize virus entering the blood
Four doses of IPV at 2, 4 & 6 to 18 months; upon entry to school at 4 to 6 years
Booster adults on entering endemic county

12. ROLE OF IMMUNIZATION Direct role in disease prevention
Western world has eradicated disease due to widespread immunization
Only three countries with disease those that are war stricken
Immunization campaign marred due to propagandas and un-education
Low socioeconomic conditions further promote disease

13. INACTIVATED & ORAL POLIO VACCINES
Killed (Salk)
Live (Sabin)
Attribute
Yes
Prevents disease No
Interrupts transmission
Induces humoral IgG
Induces intestinal IgA
Affords secondary protection by spread to others
Interferes with replication of virulent virus in gut
Yes (rarely)
Reverts to virulence
Can cause disease in the immunocompromised
Injection
Oral
Route of administration
Requires refrigeration
Shorter
Longer
Duration of immunity

14. PRION DISEASE
Prions are protein-containing particles with no detectable nucleic acid
"Slow" infectious diseases
Highly resistant infectious agent
No inflammation or immune response in affected

15. PRION DISEASES-SPONGIFORM ENCEPHALOPATHYIP
Host
Agent
Disease
Months to years
Humans, chimpanzees, monkeys
Prion
CJD: classical, familial, sporadic form
Humans, cattle
Variant CJDa
Kuru
DISEASES OF ANIMALS
Sheep, goats, mice, hamsters
Scrapie
Cattle
Bovine spongiform encephalopathy
Months
Mink, other animals
Transmissible mink encephalopathy
Mule deer, elk
Chronic wasting disease

16. PRION DISEASES PATHOGENESIS
BASIC CHARACTERISTICS OF ALL PRION DISEASES
Transmissible spongiform encephalopathies
Non conventional viruses
Proteinaceous material without nucleic acid
Diseases are confined to the nervous system
Neuro-degeneration and spongiform changes
Amyloid plaques may be present
Long incubation periods (months to decades)
Always fatal, no cases of remission or recovery

17. PRION DISEASES PATHOGENESIS
Kuru & vCJD mainly spread by ingestion
CJD also spread by blood transfusion
Iatrogenically via corneal transplants, dura mater grafts, implanted brain electrodes, and growth hormone extracts made from human pituitary glands

18. PRION DISEASES PATHOGENESIS
Infective material survive acid digestion
Penetrate gut mucosa
Prion Protein amplified in follicle dendritic cells in lymphatic tissue
Prions then spread to the spleen
Prions spread to CNS probably via the sympathetic nerves
Normal PrPC to the infectious form (PrPSc)-pathology

19. PRION DISEASES CLINICAL FEATURES
Relatively late in life
Rapidly progressive dementia
Behavioural disturbances
Ataxia
Death within one year
No effect of antimicrobials
Prion disease cerebrum

20. PRION DISEASES Resistant to proteolytic degradation
Highly resistant to inactivation by heat, formaldehyde, and ultraviolet light
Prions are resistant to the temperatures usually employed in cooking (imp in vCJD)
Inactivated by protein- and lipid-disrupting agents such as phenol, ether, NaOH, and hypochlorite
Instruments be sterilized using hypochlorite esp tonsillectomy instruments
Autoclaving inactivates prion (121oC at 15 lb/in2 for 20 min)