Polio Lecture 12

What are the different outcomes of Viral Infection?

Viruses differ greatly in their virulence. There are usually striking differences in the outcomes of infection of animals with the same virus.

What are the mechanisms of a viral pathogenes?

1. Binding to host cell and invasion:

• Tolerate conditions of hot environment where target cells are

• Needs a specific receptor. No specific receptor = no infection

• Spreads from one cell to another or via blood/lymph to other sites

• Replication efficiency power in numbers!

2. Avoid Immune Response

• Avoid Interferons: Shuts down host protein expression

• Avoid death of host cell: Inactivate p53 the apoptosis inducer

• Avoid antibodies: Move from one cell to the next or form syncytium Rapid evolution of surface antigens. Hide inside phagocytes/immune cells.

What is the definition of Poliomyelitis?

Muscle atrophy caused by infection of motor neurons by Polio Virus

What are the main molecules that are in the structure of a Polio virus?

1. Isosahedral

2. Naked virus (No envelope)

3. ss +RNA

4. CD155 Receptors on host cells

5. Humans are the only Natural host but virus can be grown in monkey kidney cells or transgenic mice expressing CD155

What are the Polio’s virus pathogenesis? (Whats number one?)

1. Polio virus transmission occurs via fecal-oral route.

• Enters orally and infects cells of the throat and intestinal tract (Common areas with poor sanitation and hygiene, very stable in harsh environments/resistant to disinfection)

• 99% people asymptomatic or show mild throat/digestive symptoms. These people shred and spread the virus for 4-6 weeks in their stool regardless of symptoms. Interferon response controls viral titers.

What are the Polio’s virus pathogenesis? (Whats number two?)

2. In 1% infected polio virus spreads from digestive tract and eventually can infect motor neurons of the spinal cord via the blood stream.

What are the Polio’s virus pathogenesis? (Whats number three-five?)

3. Infected motor neurons die cutting off electrical signals to muscles

4. Muscles weakness and flaccid paralysis result. Muscle lose tone and responsiveness and show atrophy (shrivel)

5. Later in life some develop post polio syndrome

How does the Polio virus get into the cell?

1. Receptor mediated endocytosis

2. Release and protein synthesis

3. Replicase made. Viral proteases shut off host machinery

4. Replication of RNA

5. Translation packaging

6. Release via lysis or exocytosis

Why do Polio viruses (PV) infected cells die

1. Virus induces cell death

2. Cells undergoes programmed cell death aka apoptosis

What are the infection symptoms for the polio virus?

99% infected: Asymptomatic or mild throat and/or digestive symptoms or mild fever

1% infected develop paralytic polio: Headache, fever, stiff neck, muscle spasms, flaccid paralysis of muscles-limbs, chest. Respiratory paralysis in severe cases.

Epidemiology of the Disease Polio

Most susceptible population to “infection”: Children <5 years

Endemic (regularly found)

• Poor sanitation

• Children infected when vary young

• Few paralytic

Epidemic (widespread occurrence at a time)

• Good sanitation

• Children are not routinely exposed (no natural immunity)

• Epidemic —> all ages are infected; increase in paralytic form

What are the Polio Diagnosis in both Symptomatic and Asymptomatic people?

1. Virus isolation in culture from stool sample collected as early after infection as possible is the most sensitive method to diagnose polio virus infection

2. Real-time reverse transcription PCR of stool sample can also be used for diagnosis and to differentiate possible wild strains from vaccine-like strains

3. Partial genome sequencing is used to confirm the polio virus genotype and determine its likely geographic origin

4. In unvaccinated people, serological tests using Indirect ELISA assays can be used for later in the infection.

Is there a Polio Treatment?

No “cure” for polio exists. The focus is on increasing comfort, speeding recovery and preventing complication

Supportive treatments includes:

Bed rest, Pain relievers, portable ventilators to assist breathing, moderate exercise/physical therapy, A nutritious diet.

What are the Polio prevention?

Vaccine options:

Sabin - Oral, attenuated, OPV

• Replicates in GI cells

• IgG and IgA response

• Prevents spread

Salk - Injected, activated, IPV

• Primarily an IgG response

• Does not prevent spread