CSB351Y1 Lecture Notes - Lecture 21: Polio Vaccine, Herd Immunity, Poliomyelitis
26 May 2018
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Lecture 21: Polio Pathogenesis and treatment/ Rhinoviruses
Poliovirus, a prototype of Enterovirus
• Geographic – worldwide, poor hygiene
• Host range – humans and chimpanzees
• Genetics – 3 serotypes
• Rapid mutation upon replication in human gut – single vaccination protective for entire life
Transmission
• Oral-fecal route and nasopharyngeal (throat)
• Infection can cause viremia (virus in blood) but major site of growth is in GALT (gut associated lymph tissue)
• Virus replicates in intestine, CNS and lymphoid tissues
• Virus excreted in stool, mainly affects children under 5
• Spread through person-to-person contact
• Herd immunity – sufficient number of children fully immunized, virus unable to infect children and dies out
• Flies can transmit feces to food, no signs of illness and can silently spread before first case of polio paralysis
Clinical features of infection and pathology
• Asymptomatic (90%) – no sign of infection, virus limited to oro-pharynx and gastrointestinal tract
• Abortive poliomyelitis – flu-like illness but clear up after
• Invasion of CNS – meningitis (inflammation in brain), muscle spasm but no paralytic symptoms
• Paralytic poliomyelitis (0.1-2%) – a little after infection, significant residual paralysis (10% fatal)
- Severity depends on type of infected neuron (flaccid without loss of sensations or irreversible paralysis)
- Virus destroys nerve cells that activate muscles as it multiplies
- Acute flaccid paralysis (AFP) – limb is floppy and lifeless
Prevention and Control of Polio
• Two types of vaccines – Salk and Sabin
• Salk (IPV) – inactivated polio vaccine, formalin killed, does not affect cells, act on GI tract (IgG)
• Sabin (OPV) – live attenuated strains, oral polio vaccine, cause minimum infection, GI, blood, GALT (IgG and IgA)
• Postpolio syndrome (PPS) – late developing complication previously infected with wild polio (fatigue, muscle
atrophy, joint, muscle pain)
Vaccine-associated Paralytic Poliomyelitis (VAPP)
• New polio incidences found due to unvaccinated individuals
• Sabin (live poliovirus) reverted to acquire increased virulence, re-evolution
Rhinovirus
• Major causative agents of common cold (over 100 known serotypes)
• Restricted to humans due to lack of appropriate cell receptors in non-human hosts
• 90% HRV use extracellular adhesion molecule ICAM-1 as receptor
• VP1,2,3 and VP4, rhinovirus also belons to picornavirus (+senseRNA) and has same mechanism (ICAM receptor)
• Transmission – airborne and direct contact, major site of infection in nasal mucosa (33 degrees in nose)
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Document Summary
Poliovirus, a prototype of enterovirus: geographic worldwide, poor hygiene, host range humans and chimpanzees, genetics 3 serotypes, rapid mutation upon replication in human gut single vaccination protective for entire life. Clinical features of infection and pathology: asymptomatic (90%) no sign of infection, virus limited to oro-pharynx and gastrointestinal tract, abortive poliomyelitis flu-like illness but clear up after. Invasion of cns meningitis (inflammation in brain), muscle spasm but no paralytic symptoms: paralytic poliomyelitis (0. 1-2%) a little after infection, significant residual paralysis (10% fatal) Severity depends on type of infected neuron (flaccid without loss of sensations or irreversible paralysis) Virus destroys nerve cells that activate muscles as it multiplies. Acute flaccid paralysis (afp) limb is floppy and lifeless. Vaccine-associated paralytic poliomyelitis (vapp: new polio incidences found due to unvaccinated individuals, sabin (live poliovirus) reverted to acquire increased virulence, re-evolution.
