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Picornavirus
Pico + RNA = Picorna
•Virion is a naked, small (25 to 30 nm) icosahedral capsid enclosing
a single-stranded
positive
RNA genome.
Box 56-2. Unique Properties
of Human Picornaviruses
•Enteroviruses are resistant to pH 3 to pH 9, detergents, mild
sewage treatment, and heat.
•Rhinoviruses are labile at acidic pH; optimum growth temperature
is 33° C.
•Genome is an mRNA. (+ sense)
•Naked genome is sufficient for infection.
•Virus replicates in cytoplasm.
•Viral RNA is translated into polyprotein, which is then cleaved into
enzymatic and structural proteins.
•Most viruses are cytolytic
Picornaviridae
•Enterovirus
•Poliovirus types 1, 2, and 3
Body_ID: B056001
•Coxsackie A virus types 1 to 22 and 24
•Coxsackie B virus types 1 to 6
•Echovirus (ECHO virus) types 1 - 9, 11 - 27, 29 - 34
•Enterovirus 68 to 71 and 73 to ….
• Parechovirus (formerly echovirus 22,23)
• Kobuvirus: Aichi virus and Ljungan virus
•Hepatovirus
-Hepatitis A virus
•Rhinovirus types 1 to 100+
Animal viruses:
•Cardiovirus
•Aphthovirus ….
• eIF4G cleaved  cellular protein
synthesis is shut off
Kozak
sequence
(NNNPuNNA
UGG )
The initiation
AUG codon in
the polio virus
open reading
frame is
preceded by
eight other
AUGs.
RCCAUGG
RYYAUGG (R
= purine, Y =
pyrimidine);
Disease Mechanisms of Picornaviruses
•Enteroviruses enter via the oropharynx, intestinal mucosa, or upper respiratory
tract and infect
the underlying lymphatic tissue; rhinoviruses are restricted to the
Body_ID: B056003
upper respiratory tract
•In the absence of serum antibody, enterovirus spreads by viremia to cells of
a receptor-bearing target tissue
•Different picornaviruses bind to different receptors, many of which are
members of the immunoglobulin superfamily (i.e., ICAM-1)
•The infected target tissue determines the subsequent disease
•Viral, rather than immune, pathologic effects are usually responsible for
causing disease symptoms
•The secretory antibody response is transistory but can prevent the initiation
of infection
•Serum antibody blocks viremic spread to target tissue, preventing symptoms
•Enterovirus is shed in feces for long periods
•Infection is often asymptomatic or causes mild, flulike or upper respiratory
tract disease
Epidemiology of Enterovirus Infections
Body_ID: B056004
Disease/Viral Factors
•Nature of disease correlates with specific enterovirus and
age of person
•Infection often asymptomatic, with viral shedding
•Virion resistant to environmental conditions (detergents,
acid, drying, mild sewage treatment, and heat)
Transmission
•Fecal-oral route: poor hygiene, dirty diapers (especially in
daycare settings)
•Ingestion via contaminated food and water
•Contact with infected hands and fomites
•Inhalation of infectious aerosols
Body_ID: PB056004
Who Is at Risk?
Body_ID: B056004
•Young children:
at risk for polio (asymptomatic or mild disease)
•Older children and adults: at risk for polio (asymptomatic to paralytic disease)
•Newborns and neonates: at highest risk for serious coxsackievirus and enterovirus disease
Geography/Season
•Viruses have worldwide distribution; wild-type polio virtually eradicated in developed
countries because of vaccination programs
•Disease more common in summer
Modes of Control
Body_ID:
PB056004
•For polio, live
oral
polio vaccine (trivalent OPV) or inactivated trivalent polio vaccine (IPV)
is administered
•For other enteroviruses, no vaccine; good hygiene limits spread
Poliovirus infection
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Asymptomatic illness results if the viral infection is
limited to the oropharynx and the gut. At least 90% of
poliovirus infections are asymptomatic.
Abortive poliomyelitis, the minor illness, is a
nonspecific febrile illness occurring in approximately
5% of infected people. Fever, headache, malaise, sore
throat, and vomiting occur in such people within 3 to 4
days of exposure.
Nonparalytic poliomyelitis or aseptic meningitis
occurs in 1% to 2% of patients with poliovirus
infections. In this disease, the virus progresses into the
central nervous system and the meninges, causing
back pain and muscle spasms in addition to the
symptoms of the minor illness.
•
Paralytic polio, the major illness, occurs in 0.1% to 2.0% of
persons with poliovirus infections and is the most severe outcome.
It appears 3 to 4 days after the minor illness has subsided, thereby
producing a biphasic illness. In this disease, the virus spreads
from the blood to the anterior horn cells of the spinal cord and to
the motor cortex of the brain. The severity of paralysis is
determined by the extent of the neuronal infection and by which
neurons are affected. Spinal paralysis may involve one or more
limbs, whereas bulbar (cranial) paralysis may involve a
combination of cranial nerves and even the medullary respiratory
center.
•
Paralytic poliomyelitis is characterized by an asymmetrical
flaccid paralysis with no sensory loss. Poliovirus type 1 is
responsible for 85% of the cases of paralytic polio. Reversion of
the attenuated vaccine virus types 2 and 3 to virulence can cause
vaccine-associated disease.
Coxsackievirus and Echovirus Infections
• Herpangina
Type A 1-10
Type B 1-5
Echoviruses
Mostly in children; epidemicin summer months
Abrupt fever, sore throat, anorexia, abdominal pain
and vesicles on soft palate, pharinx and tonsills
Hand-foot-and-mouth disease
• Coxsackie A16, 4, 5, 10
Myocardial and pericardial
infections
• Coxsackie B, echovirus
• Sudden onset Diabetes: Coxsackie B 4
Viral (aseptic) meningitis
• Coxsackie A, B
• Echovirus
• Summer and fall
Fever, rash, and common
coldlike symptoms
• Summer minor illnes:
Rubelliform rush on face, neck and chest
Accompanied by fever
No distinctive feature
Short duration
Plerodynia
• Coxsackie B
• Sudden chest pain, fever, malaise
• (Abdominal or testicular pain)
Laboratory Diagnosis
• CSF findings
• Culture
• Molecular and serological methods
Treatment and Prevention
• Vaccine available only for Polio
Rhinoviruses
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Epidemiology of Rhinovirus Infections
Disease/Viral Factors
Virion is resistant to drying and detergents
Multiple serotypes preclude prior immunity
Replication occurs at optimum temperature of 33° C and cooler
temperatures
Transmission
Direct contact via infected hands and fomites
Inhalation of infectious droplets
Who Is at Risk?
People of all ages
Geography/Season
Virus found worldwide
Disease more common in early autumn and late spring
Modes of Control
Washing hands and disinfecting contaminated objects help prevent spread