CNS Infections- Polio Virus Flashcards Preview

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Flashcards in CNS Infections- Polio Virus Deck (34):

Poliomyelitis (myelitis = inflammation of spinal chord) is an acute systemic infectious disease.
In its rare, severe form, it affects CNS, destroying motor neurons in spinal cord, which results in a _____________.

flaccid, ascending, asymmetrical paralysis. Old name is infantile paralysis


Another name for Polio virus is

Human Enterovirus C


Polio is an enterovirus - Human Enterovirus C- description

-Polio viruses
-a non-enveloped
+sense RNA virus
-3 serotypes designated as PV1, PV2, and PV3


infection with one serotype results in lifelong immunity but they __________
An adequate vaccine must contain __________.

do not cross neutralize

all three types (i.e., is trivalent)


Polio is rare today in US due to vaccination. Polio was thought to be primarily a disease of _________. Most cases occurred in slightly __________ who manifested with more serious disease.

developed/industrialized countries

older, susceptible children and young adults


Paralytic polio is a significant concern in ____________

underdeveloped countries


Infection is acquired from an infected or diseased person, primarily by the ____________.

fecal-oral route via contaminated food and water; virus is present in stool 3-6 weeks.

-less so by respiratory secretions/aerosol droplets and saliva (oral-oral transmission)


Host of Polio

Humans are the sole host (the virus only infects humans). Transmission occurs most frequently by persons with inapparent infections.


Reservoirs of Polio

humans AND water


How communicable is Polio?

Highly communicable: Poliovirus is highly infectious, with seroconversion rates in susceptible household contacts of children nearly 100% and of adults over 90%


Populations affected by Polio (list)

1. **children less than 3 are primarily affected** (in utero, neonatal, infant infections DO NOT normally occur)
2. adolescents and young adults, esp. pregnant women are also susceptible.
3. the elderly
3. Younger pt have less severe manifestations. The likelihood of developing paralytic polio increases with age, as does the extent of paralysis (one limb vs quadriplegia)


Seasonality/temporal pattern

Summer-fall (in temperate zone, i.e., Northern hemisphere), little seasonality occurs in the tropics


Common pathogenesis/presentation

S/S: no symptoms (majority) or mild malaise


Polio is a _____ virus. After virus enters the mouth or nose, the virus infects cells and then spreads to _____________, first in pharynx and later in the intestinal tract where infection can persist for _________ and the patient may manifest with signs and symptoms. The virus is shed in _______ for several weeks and in the feces for several months. A viremia will also occur. Rarely, the viremia is ______.


draining lymph nodes along the GI tract

weeks to months

oral secretions



Rarely, the virus enters the CNS by:

1. crossing the blood-brain barrier
2. travels by neural routes (infects skeletal muscle, then travels up innervated nerves of skeletal muscles) and along the PNS via retrograde axoplasmic flow as per herpes, and/or rabies viruses to CNS


Once in the CNS, poliovirus spreads along certain nerve fiber pathways, preferentially replicating in and destroying motor neurons within ___________. This leads to the development of _________, the various forms of which (spinal, bulbar, and bulbospinal) vary only with the amount of neuronal damage and inflammation that occurs, and the region of the CNS that is affected.

the spinal cord, brain stem, or motor cortex

paralytic poliomyelitis


Spread through CNS results in

lower motor neuronal damage (FLACCID PARALYSIS) with NO sensory loss (unlike GBS)


Inapparent/Asymptomatic infection is the most common (90→95%); however disease form manifests in 4-8% of people with these S/S:

-Minor illness/gastroenteritis/abortive poliomyelitis is most common
- fever, malaise, fatigue, drowsiness,
-headache, muscle aches
-sore throat/pharyngitis
-nausea and vomiting, abdominal pain, constipation, rarely diarrhea
-Lasts 72 hours or less


Polio also manifest as Aseptic meningitis without paralysis/non-paralytic

(Abortive illness/Abortive polio (3rd most common form) — Signs and Symptoms of aseptic meningitis described earlier plus:

-Pain in front part of neck
-Back pain or backache
-Muscle stiffness, Leg pain (calf muscles)
-Muscle tenderness and spasm in any area of the body
-Pain or stiffness of the back, arms, legs, abdomen
Symptoms usually last 1 - 2 weeks


Least (0.1 →2%) common form of diease is paralytic poliomyelitis, S/S:

Initially Signs and Symptoms of aseptic meningitis without paralysis, but is FOLLOWED BY an asymmetric flaccid paralysis that is
ascending, acute onset, with a fever.


During the rare paralytic poliomyelitis, paralysis begins 1→ 10 daysafter the early symptoms began. It progresses for two to three days and is usually complete by the time the fever breaks. S/S are:

-Severe muscle aches or spasms, muscle pain
-Loss of superficial and deep reflexes (Diminished deep-tendon reflexes/areflexic leg weakness).
-EMG velocity studies demonstrate axonal-type polyneuropathy affecting anterior horn cells or their axons vs. demyelination


Sensory involvement of paralytic poliomyelitis is

abnormal sensations (but not loss of sensation) in an area; sensitivity to touch, paresthesia.


3 forms of paralytic poliomyelitis – 3 Different types of paralysis may occur, depending on the nerves involved:

1. Spinal
2. Bulbar polio
3. Bulbospinal polio
-for some patients, paralysis is temporary, lasting weeks


Post-polio Syndrome manifests as:

-unaccustomed fatigue
-new or recurrent muscle weakness and pain
-progressive muscle atrophy
-Peak incidence is 30 → 40 years following acute polio
-Disease develops when patient's remaining motor units/motor neurons start to respond poorly due to their overuse throughout many years. NOT due to activation of latent poliovirus


Differential diagnosis of acute flaccid paralysis:

1. ECHO, Coxsackie and Enterovirus 68→71,
2. arbovirus
3. polio/post polio vaccination.
4. tick paralysis.
5. Guillain-Barré’-Syndrome.
6. botulism.
7. dumb rabies.
8. myasthenia gravis.
9. intoxication due to poisons.


Diagnosis is usually made by identifying poliovirus in stool sample, but it may also be identified by

direct amplification from stool specimens followed by partial genomic sequencing to establish identity and possible source of the virus. (rarely detected in blood of CSF)


Treatment and Prophylaxis

Tx: supportive
1. Inactivated (killed) polio vaccine (IPV)
2. Enhanced potency vaccine (e-IPV)
3. Oral polio vaccine (OPV) aka Sabin


Inactivated (killed) polio vaccine (IPV) description

-AKA Salk vaccine
-is trivalent
-is prepared by formalin inactivation of wt virus grown in primate tissue culture.
-Primary series is at least 4 inoculations over a 1→ 2 years
-High efficacy due to seroconversion/immunity
(> 90%)


Enhanced potency vaccine (e-IPV) description

-is more potent than original IPV
-is the only IPV vaccine approved in US, i.e., IPV = e-IPV


Advantages of e-IPV (newer, more used version of IPV)

-Safe/no risk for unvaccinated persons, e.g., the immunocompromised.


Limitations of e-IPV (newer, more used version of IPV)

1. Given parentally (i.e., injected) – more expensive than Oral polio vaccine (OPV) administration.
2. Does not generate high sIgA responses but rather a serum IgG response. This response is still efficacious since if a vaccinated person is exposed to WT virus, the WT virus must first disseminate in blood and lymphatics before reaching the CNS, and serum anti-polio-IgG helps clear virus from these sites.
3. Boosters are needed. In developing countries, a 4th booster may be required.
4. Only protects those actually vaccinated. So religious/philosophical groups not participating in vaccine program can/do occasionally become infected in local outbreaks → the spread of wild-type (wt) virus.


Oral polio vaccine (OPV) aka Sabin description

-trivalent vaccine
-live attenuated virus which replicates in oropharynx and intestinal tract but cannot infect neuronal cells, less transimisable than wt virus.
-OPV has significant advantages over e-IPV


Limitations to Oral polio vaccine (OPV) Sabin

1. Puts other unvaccinated family members and contacts at risk, may spread to immunocompromised persons. (bc live virus)
2. During viral replication in vaccinated children, the attenuated virus mutates back to the virulent/wt virus , but only causes extremely rare cases of vaccine-associated paralytic polio/poliomyelitis (VAPP) in the US (8→10 cases/year).
3. Vaccine-derived poliovirus can actually circulate in the population, (cVDPV)


Current vaccine recommendations

4 doses e-IPV (IPOL) ONLY