POLIOMYELITIS & PRION
DISEASE
Assist Prof
Dr. Syed Yousaf Kazmi
LEARNING OBJECTIVES
1. Discuss etiology, pathogenesis and
epidemiology of poliomyelitis
2. Explain the role of immunization on
epidemiology of poliomyelitis
3. List various prion diseases
4. Discuss etiology, pathogenesis and
transmission of Prion disease
5. Discuss the role of sterilization & disinfection
in transmission of prion disease
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
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
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
POLIOMYELITIS-CURRENT STATUS
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 gutlymphoid organs
 Viremia-Virus reach CNS
 Aseptic meningitis
PATHOGENESIS
 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
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
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
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 uneducation
 Low socioeconomic conditions
further promote disease
INACTIVATED & ORAL POLIO
VACCINES
Attribute
Live (Sabin)
Killed (Salk)
Prevents disease
Yes
Yes
Interrupts transmission
Yes
No
Induces humoral IgG
Yes
Yes
Induces intestinal IgA
Yes
No
Affords secondary protection by spread Yes
to others
Interferes with replication of virulent Yes
virus in gut
Reverts to virulence
Yes (rarely)
No
Can cause disease in the
immunocompromised
Route of administration
Yes
No
Oral
Injection
Requires refrigeration
Yes
No
Duration of immunity
Longer
Shorter
No
No
PRION DISEASE
Prions are proteincontaining particles with no
detectable nucleic acid
"Slow" infectious diseases
Highly resistant infectious
agent
No inflammation or immune
response in affected
PRION DISEASES-SPONGIFORM
ENCEPHALOPATHY
Disease
Agent Host
IP
CJD: classical, familial, Prion
sporadic form
Variant CJDa
Prion
Humans, chimpanzees, monkeys
Months to years
Humans, cattle
Months to years
Kuru
Prion
Humans, chimpanzees, monkeys
Months to years
Prion
Sheep, goats, mice, hamsters
Months to years
Cattle
Months to years
Mink, other animals
Months
Mule deer, elk
Months to years
DISEASES OF ANIMALS
Scrapie
Bovine spongiform
Prion
encephalopathy
Transmissible mink
Prion
encephalopathy
Chronic wasting disease Prion
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
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
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
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
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)