Unit 3 - Polio Virus & Other Enteroviruses Flashcards
1
Q
Describe a breif overview of Enteroviruses
A
- Small RNA viruses
- Naked
- Picornaviridae family
- Ubiquitous in nature
- “Entero” means intestine: transmitedd by an oral-fecal route
- Over 70 distinct types of human enteroviruese: 20 recongizable clinical syndromes
2
Q
What is the history of Polio?
A
- Descriptions of poliomyelitis date to 1500 bc
- Egyptian stele showing “foot drop”
- Existed quietly for thousands of years as an endemic pathogen
- Significant problem in northern Europe in the 1880s
- Major epidemics largely unknown before the late 19th century
- The 1916 New York City epidemic was one of the worst.
- Poliomyelitis is rare today because of vaccination efforts.
- Last cases of poliomyelitis in the US were in 1979 and 2005
- unvaccinated persons from Amish communities
3
Q
Why is polio a public health concern?
A
- Disease of mysterious, seasonal appearance by 1910
- It could paralyze respiratory muscles
- 1 in 1,000 infected children
- 1 in 75 infected adults
- Infection had disfiguring, crippling, and sometimes fatal outcomes
4
Q
What are the clinical features of Poliomyelitis?
A
- Portal of entry: mouth
- Person to person spread: oral–fecal route
- Infants appear to be the most efficient transmitters of infection.
- e.g., direct contact with feces when changing diapers or poor sanitary conditions
- Average incubation period: 6–20 days
- Poliovirus may be present in stool for 3–6 weeks and 2 weeks in saliva.
5
Q
What are the course of Mild infections?
A
- Variable
- 95% of all poliovirus infections are asymptomatic
- Asymptomatic persons shed virus in stool and are able to transmit the virus to others.
- About 4%–8% of poliovirus infections cause mild symptoms:
- Malaise
- Gastrointestinal distress
- Fever
- Influenza-like illness
- Sore throat
- Complete recovery occurs within a week.
- 1-2% of polio infections are associated with:
- Minor illness followed by stiff neck/back, and/or legs
- These symptoms last 2–10 days followed by a complete recovery
6
Q
What are the course of Major Illness?
A
Occurs in less than 1% of all poliovirus infections
- Flaccid paralysis = weakness
- Inflammation and occasional destruction of neurons
- Recovery can take up to two years and may be incomplete.
- Weakened muscles (see Figure 11-3)
7
Q
What are the Three forms of Major illness?
A
- Spinal Paralysis
- Bulbar
- Bulbospinal
8
Q
What is Spinal Paralysis?
A
- Most common
- Viral invasion of the motor neurons of the anterior horn
- Without nerve stimulation, muscles atrophy and become weak, floppy and poorly controlled, finally becoming completely paralyzed
- Asymmetric paralysis (occurs on one side)
9
Q
What is Bulbar?
A
- Less common (2% of cases of paralytic polio)
- Invasion & destruction of nerves within the bulbar region of the brain stem
- Weakening of muscles involved in breathing, speaking, and swallowing
- Patient may require an iron lung or respirator
10
Q
What is Bulbospinal?
A
- 19% of all cases of paralytic polio
- Combination of spinal and bulbar paralysis
11
Q
What is Post-Polio Syndrome? (PPS)
A
- Occurs in 25-50% of individuals who recovered from childhood paralytic polio
- Insidious; occurs 8–71 years post-polio infection
- Average onset is 36 years post-recovery
- More common in women than men
- Not an infectious process (no viral shedding)
- Most common symptoms:
- New weakness in muscles or limbs involved at the time of acute poliomyelitis
- Extreme fatigue
- Pain in the muscles and joints
12
Q
What causes PPS?
A
- Muscle fibers of surviving motor neurons slowly deteriorate over time.
- Nerve endings are eventually destroyed and permanent weakness occurs.
- Effective management requires an interdisciplinary approach
- manage pain, fatigue, anti-inflammatory therapy, etc.
13
Q
What is the classicfication and Structure of Poliovirus?
A
- Member of the Picornaviridae family
- Small, 30 nm in diameter
- Icosahedral-shaped
- Non-enveloped
- Acid-stable
- (+) ssRNA genome ~7441 nucleotides in length
14
Q
What is the stability of enteroviruses in the Environment?
A
Resistant to:
- pH levels less than 3 (stomach acid)
- Digestion by most proteases
- Detergents
- 70% alcohol
- Solvents (e.g., ether and chloroform)
- Disinfectants (e.g., 5% Lysol, 1% QUATS)
- May be stable several days to several weeks at 4oC (39.2oF)
15
Q
What are the inactivation/Disinfection Protocols?
A
- Chlorine bleach
- Hydrochloric acid
- Aldehydes
- Heat 50oC (122oF) for one hour (in the absence of calcium and magnesium)
16
Q
What are the Laboratory Diagnosis of Poliovirus Infections?
A
- Most common method: isolate virus from stool samples or swab of the pharynx
- Grows well in characterized in any human or monkey kidney cell lines (causes good CPEs)
- Identify serotype with neutralization assays
- Nucleic acid methods: PCR and sequencing used to determine if the infection is caused by “wild-type” virus (encountered in nature) or “vaccine” virus
17
Q
What is the cellular Pathogenesis?
A
- Humans and non-human primates are the only known natural hosts of polioviruses.
- Does not infect other experimental animals (e.g., mice)
- Likely due to the lack of poliovirus receptor
- Once ingested, polioviruses invade two lymphoid tissues:
- Peyer’s patches (aggregations of lymphoid tissue on small intestine)
- Tonsils
18
Q
How does Poliovirus Spread through the bloodstream?
A
- Major viremia: flu-like symptoms; sore throat; headache; fever
- Penetration of the CNS appears to be incidental & provides no known benefit to the virus
19
Q
What is the small percent of patients who have poliovirus?
A
- Polioviruses carried via the bloodstream to the anterior horn cells of the spinal cord
Results in lesions in the spinal cord and brain
- Motor neuron destruction
- Paralysis
- Respiratory arrest
- Death
21
Q
Polio Entry
A
34
Q
What was the Sabin Strain Attenuation/Passaging Process?
A
- Attenuation process “weakened” virus by introducing mutation in IRES region
Three Strains:
- Sabin Type 1 - Strain Mahoney 1
- Sabin Type 2- Strain P712
- Sabin Type 3 - Strain Leon III
