poliomyelitis_EPIDEMIOLOGY_presentation.pptx

POLIOMYELITIS
INTRODUCTION, EPIDEMIOLOGY, ETIOLOGY, PATHOGENESIS,
CONTROL, AND PREVENTION

INTRODUCTION
 Poliomyelitis (polio) is a highly infectious viral disease caused by the
poliovirus, which primarily affects the nervous system, leading to muscle
weakness, paralysis, and, in severe cases, death.
 It is a significant public health concern, particularly in developing
nations, where sanitation and vaccination coverage may be inadequate.
 The disease predominantly affects children under five years of age,
though individuals of any age can be infected.
 With the advent of widespread immunization, polio has been largely
eradicated in most parts of the world, but sporadic outbreaks still occur
in endemic regions.

EPIDEMIOLOGY OF
POLIOMYELITIS
Polio was once a global health burden,
causing widespread outbreaks. However,
vaccination efforts have eliminated the
disease in most countries, with only a few
remaining endemic areas.
Key Epidemiological Factors:
Global Burden:
 Before the introduction of vaccines, polio
was a major cause of permanent
disability worldwide.
 The Global Polio Eradication Initiative
(GPEI), launched in 1988, significantly
reduced cases by over 99%.
 Currently, polio remains endemic in only
Pakistan and Afghanistan, though
vaccine-derived poliovirus (VDPV) cases
have been reported in some other
countries.
Reservoir:
Humans are the only natural reservoir
of the poliovirus. No animal reservoirs
have been identified.

Mode of Transmission:
 Fecal-oral route: The virus spreads
through contaminated food, water, or
hands.
 Oral-oral route: Direct transmission
through respiratory secretions can also
occur.
 The virus can persist in the environment
for weeks under favorable conditions.
Risk Factors:
 Poor sanitation and hygiene
 Lack of immunization
 Crowded living conditions
 Malnutrition, which weakens immunity
 Travel to polio-endemic areas
Incubation Period:
Typically 7–14 days, but can range
from 3–35 days.
Seasons and Trends:
Polio outbreaks are more common
in summer and fall in temperate regions,
while transmission is year-round in tropical
areas.
EPIDEMIOLOGY OF
POLIOMYELITIS

ETIOLOGY OF
POLIOMYELITIS
Polio is caused by the poliovirus, a member of the
Picornaviridae family and the Enterovirus genus.
Poliovirus Characteristics:
Structure:
• Small, non-enveloped RNA virus (~30 nm in
diameter).
• Single-stranded positive-sense RNA genome.
• Stable in the environment and resistant to
detergents and mild disinfectants.
Types of Poliovirus:
1. Wild Poliovirus (WPV)
• Three serotypes:
• Type 1 – Most virulent and
responsible for most cases of
paralysis.
• Type 2 – Eradicated in 1999;
caused vaccine-derived
outbreaks.
• Type 3 – Declared eradicated in
2019.
2. Vaccine-derived poliovirus (VDPV)
Occurs when the weakened virus from the
oral polio vaccine (OPV) mutates in under-
immunized populations.

PATHOGENESIS OF
POLIOMYELITIS
Entry and
Primary
Replication
: The virus
multiplies in
the
oropharynx
and
intestines.
Viremia and
Spread: The
Virus enters
the
bloodstream
and spreads
to target
organs.
CNS
Invasion:
Virus infects
motor
neurons,
causing
paralysis.
Neuronal
Damage:
Destruction
of anterior
horn cells
leads to
muscle
weakness.
Outcomes:
Asymptomatic
, abortive
polio, non-
paralytic polio,
paralytic polio,
post-polio
syndrome.

The pathogenesis of polio involves viral invasion,
multiplication, and destruction of motor
neurons, leading to paralysis.
 Stages of Infection:
1. Entry and Primary Replication:
 The virus enters the body through the
mouth via contaminated food or water.
 It initially multiplies in the oropharynx
and intestine.
2. Viremia and Spread:
After local replication, the virus enters the
bloodstream (viremia) and spreads to other
organs, including the central nervous
system (CNS).
3. CNS Invasion:
 The virus crosses the blood-brain
barrier or infects motor neurons via
retrograde axonal transport.
 It primarily targets the anterior horn
cells of the spinal cord and brainstem.
 Infected motor neurons undergo
necrosis and apoptosis, leading to
flaccid paralysis.
 Severity depends on the extent of
neuronal destruction.
 In bulbar polio, involvement of the
brainstem can lead to respiratory
failure.
5. Outcomes:
 Asymptomatic (90–95%) – Most
infections do not cause symptoms.
 Abortive polio (4–8%) – Mild illness
with fever, sore throat, and
gastrointestinal symptoms.
 Non-paralytic polio (1–2%) – Aseptic
meningitis with neck stiffness and
headache.
 Paralytic polio (<1%) – Permanent
muscle weakness or paralysis.
 Post-polio syndrome (PPS): Late-onset
PATHOGENESIS OF
POLIOMYELITIS

CONTROL AND PREVENTION OF
POLIOMYELITIS
1. Vaccination (Primary Prevention)
Vaccination is the most effective strategy for preventing polio.
 Oral Polio Vaccine (OPV):
• Live-attenuated vaccine given orally.
• Provides both systemic and mucosal immunity.
• Risk: Can mutate into vaccine-derived poliovirus
(VDPV).
• Used for mass immunization campaigns.
 Inactivated Polio Vaccine (IPV):
• Killed virus vaccine, given via injection.
• Provides systemic immunity but not gut immunity.
• Safer but requires booster doses.
• Used in routine immunization programs.
 Global Polio Eradication Initiative (GPEI) Strategy:
• Routine immunization
• Supplementary immunization campaigns
• Surveillance of acute flaccid paralysis (AFP) cases
• Outbreak response through targeted immunization
2. Hygiene and Sanitation (Secondary Prevention)
• Improved sanitation reduces virus transmission.
• Handwashing with soap and safe drinking water.
• Proper disposal of human waste.

3. Surveillance and Early Detection
• Acute Flaccid Paralysis (AFP) surveillance: Rapid detection
of potential polio cases.
• Environmental surveillance: Testing sewage for poliovirus.
4. Outbreak Response (Tertiary Prevention)
• Mass vaccination in response to outbreaks.
• Quarantine measures in affected areas.
5. Travel Restrictions and Immunization
• Travelers from polio-endemic countries are often required to
show proof of vaccination.
• WHO recommends booster doses for travelers visiting
endemic regions.
CONTROL AND PREVENTION OF
POLIOMYELITIS

CONCLUSION
 Polio cases have drastically declined due to vaccination
efforts.
 Vaccine-derived poliovirus remains a challenge.
 Continued immunization and surveillance are crucial for
eradication.

REFERENCES
 World Health Organization (WHO)
 Centers for Disease Control and Prevention (CDC)
 Global Polio Eradication Initiative (GPEI)

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