POLIOVIRUSES

Structure & Property	Transmission	Pathogenesis	Clinical findings	Laboratory diagnosis	Treatment	
Family: picorna

Gnome: single-strand RNA, positive polarity

Size: 22-30nm

Icosahedral capsid

Nonenveloped

Acid-stable

3 serotypes	Virions accumulate in the cell cytoplasm and are released upon death of the cell – do not bud from membrane.

Transmitted by fecal-oral route and pharyngeal secretions.

Humans are only natural hosts.

No permanent carrier state occurs following infection.

Virus excretion in feces occur for several months.

Quarantine of disease is not effective because fecal excretion of virus occurs in infected individuals prior to onset of symptoms and in those who remain asymptomatic.	Replicates in oropharynx and intestinal tract, esp. in lymphoid tissue.

Spread through bloodstream to central nervous system.

Replicates in motor neuron located in anterior horn of spinal cord.

Death of these cells results in paralysis of muscles innervated by those neurons.

Immune response: intestinal IgA and humoral IgG to specific serotype.

Infection provides lifelong type-specific immunity.	Inapparent, asymptomatic infection.

Abortive poliomyelitis:
- mild febrile illness
- headache
- sore throat
- nausea & vomiting
- most patients recover spontaneously.

Non-paralytic poliomyelitis:
- aseptic meningitis
- fever, headache
- stiff neck
- resolved spontaneously

Paralytic poliomyelitis:
- flaccid paralysis
- brain stem involvement lead to respiratory paralysis.
- painful muscle spasms.	Diagnosis:
- isolation of virus
- detect rise in antibody titre.

Isolation:
- throat
- stool
- spinal fluid

Causes CPE

Serologic tests are of little value.	No antiviral therapy.

Treatment is limited to symptomatic relief and respiratory support.

Salk vaccine:
- contains 3 polioviruses inactivated by formaldehyde.
- given intravenously. 
- used in vaccination of unimmunized adults and immunodeficient individuals.

Sabin vaccine:
- contains attenuated strains of the 3 polioviruses.
- administered in oral doses at 2, 3, 4 months old.
- induce IgA in intestine.
- keep refrigerated to prevent heat inactivation.
- longer immunity
- possible reversion to virulence (rare)

Passive immunization with immune serum globulin to exposed individuals.