Picornaviruses Flashcards
The family Picornaviridae currently consists of 147 species grouped into 63 genera.
Describe infection symptoms.
Picornaviruses cause a wide range of illness in humans (more so than other virus families).
Infection with various picornaviruses may be asymptomatic, mild illness such as the common cold, or more severe disease such as aseptic meningitis and encephalitis.

What type of picornavirus is poliovirus?
A member of the Enterovirus genus.
What are enteroviruses resistant to?
Enteroviruses are resistant to many common laboratory disinfectants that would inactivate many other types of viruses.
What are enteroviruses sensitive to?
Formaldehyde, which is used to denature the virus during vaccine production.
Enteroviruses are also sensitive to chlorine at levels of 0.3 to 0.5 ppm; however, the presence of organic matter may protect the virus from inactivation by the chlorine.
This finding might explain the transmission of poliovirus by ingestion of water from swimming pools and some sources of drinking water.
What characterizes paralytic poliomyelitis?
Poliovirus causes the disease paralytic poliomyelitis and is characterized by flaccid muscular paralysis due to the death of motor neurons.
It is estimated that less than 1% of poliovirus infections result in paralytic poliomyelitis.
When did the World Health Organization launch it’s global poliovirus eradication campaign?
What was the goal?
Did they succeed?
1988.
The goal of the campaign was the worldwide eradication of poliovirus by the end of the year 2001.
The campaign has had some successes but there is still much work to do to completely eradicate poliovirus as an infectious disease.
How are enteroviruses such as poliovirus transmitted?
Enteroviruses such as poliovirus are usually transmitted from one person to the next by the fecal-oral route.
Where does poliovirus replicate initially after ingestion?
What symptoms begin to appear?
After ingestion in contaminated food or water, the virus initially replicates in the oropharyngeal mucosafor 1–2 weeks.
At this time, the infected person may be asymptomatic or experience a mild illness (e.g., sore throat).
What happens after poliovirus replicates in the oropharyngeal mucosafor 1–2 weeks?
The virus then moves through the stomach and before infecting the epithelial cells of the lower intestinal tract.
In the intestinal epithelia, the virus undergoes extensive replication and may result in a transient viremia (i.e., virus in the bloodstream).
Once in the blood, the virus may target the Central Nervous System (CNS).
Poliovirus infects certain types of nerve cells and kills these cells after when the virus egress after replication.
The infected person excretes the virus in feces for several weeks
Describe poliovirus pathogenesis based on experimental findings?
The virus initially replicates in the oropharyngeal and intestinal mucosa, and eventually reaches the blood resulting in a viremia.
Invasion of virus into the central nervous system may occur either directly from the blood, or by retrograde axonal transport when virus enters the neuromuscular junction.

What is non-paralytic polio (aseptic meningitis)?
This form of polio is characterized with the same symptoms as abortive polio, but the patient experiences stiffness and pain in neck and back that lasts for 2–10 days.
The recovery is rapid and complete.
What responses may occur after infection with poliovirus?
- subclinical infection without symptoms
- mild illness (abortive polio)
- non-paralytic poliomyelitis (also called aseptic meningitis)
- paralytic poliomyelitis
What is abortive polio?
This is the most common form of polio, occurring in more than 95% of cases.
It is characterized as a febrile illness where the patient may experience non-specific symptoms such as fever, malaise, drowsiness, headache, nausea, vomiting and sore throat.
Complete recovery occurs in a few days.
It is only recognized and confirmed if virus is detected in the blood.
What is paralytic polio?
This form of polio is the major illness and occurs in about 1% of infections.
The paralysis may or may not follow the minor illness.
The predominating sign is flaccid paralysis resulting from lower motor neuron damage.
The amount of damage and destruction by poliovirus will vary from patient to patient.
The maximal recovery usually occurs within 6 months but sometimes takes longer.
Antibodies to the virus appear early in infection, and are usually present when paralysis appears.
What is post poliomyelitis muscle atrophy (PPMA)?
A “reappearance” of paralysis and muscle wasting has been observed in some patients decades after their illness and recovery from paralytic poliomyelitis.
It is not a consequence of a persistent infection or re-infection.
It is the result of the normal decline in the function of motor neurons that had compensated for the loss in function of motor neutrons killed by poliovirus.
Describe muscles commonly weakened by poliovirus infections.
Paralysis by poliovirus may involve any muscle of the body, but the legs muscles are the most commonly affected in survivors.
The paralysis is of the flaccid type (not stiff).
Some muscles may be weak or limp.
In time, the affected limb may not be able to straighten due to contractures (shortening) of certain muscles.
The muscles and bone of the affected limb become thinner than the unaffected limb, and does not grow as fast resulting in a shorter limb.

What were the approaches to control infection to poliovirus prior to vaccine development ?
The only approaches to control infection were passive immunization and non-specific public health measures (i.e., isolation of patients and closing schools, swimming pools etc.).
These measures were not successful in preventing epidemics of poliomyelitis.
What is a serotype?
A serotype is a variant of the virus that will elicit the production of a distinct population of antibodies.
These antibodies will bind to the serotype used as the antigen, but not to other serotypes of the virus.
Therefore, infection (and subsequent antibody production) with one serotype of poliovirus does not confer protection against the other serotypes.

How many poliovirus serotypes are there?
There are three poliovirus serotypes: 1, 2 and 3.

For poliovirus, where are the epitopes responsible for production of neutralizing antibodies located?
On the structural proteins VP1, VP2 and VP3.
For poliovirus, what are most of the neutralizing antibodies against?
Most of the neutralizing antibodies are against the epitopes on VP1.
Thus, immunization with poliovirus serotype 1 will elicit the production of antibodies that recognize VP1, VP2 and VP3 proteins of serotype 1.
These antibodies will not bind to VP1, VP2 and VP3 proteins of poliovirus serotype 2.
How many forms of a poliovirus vaccine exist?
There are two forms of poliovirus vaccine available:
IPV (Inactivated Poliovirus Vaccine, injected)
OPV (Oral Poliovirus Vaccine, ingested as a syrup).
How are the three serotypes of poliovirus used in the original IPV cultivated?
Using monkey kidney cells or human cell lines.
The viruses are concentrated, purified and inactivated with formaldehyde.
The vaccine is administered by injection and requires a “booster” (repeated) vaccination.
How does IPV work as a vaccine for poliovirus?
Induces the production of protective serum antibodies (IgG).
It does not confer localized immunity (i.e., there is no secretion of IgA antibody into the mucosal lining of the GI tract) and re-infection of the alimentary tract is possible.
The implication of this observation is that such a vaccinated person may become infected with poliovirus and shed the virus in their feces for several weeks. The vaccinated person would be protected from the virus because of the antibody in the bloodstream. However, if they were to ingest water contaminated with poliovirus, they could develop a gastrointestinal infection that produces virus particles that could be transmitted to a susceptible person.






















