WHAT IS POLIOVIRUS???
Poliovirus, the causative agent of poliomyelitis, is
a human enterovirus and member of the family of
Picornaviridae. Poliovirus is composed of an
RNA genome and a protein capsid.
Enteroviruses are a genus of positive-sense
single-stranded RNA viruses associated with
several human and mammalian diseases.
A picornavirus is a virus belonging to the
family Picornaviridae. Picornaviruses are
small, non-enveloped, positive-stranded RNA
viruses with an icosahedral capsid.The viral
particle is about 30nm in diameter.
Positive-strand RNA virus: Also known as a
sense-strand RNA virus, a virus whose genetic
information consists of a single strand of RNA that is
the positive (or sense) strand which
encodes mRNA (messenger RNA) and
protein. Replication in positive-strand RNA viruses is
via a negative-strand intermediate.
A capsid is the protein shell of a virus. It consists
of several oligomeric structural subunits made
of protein called protomers. The observable 3-
dimensional morphological subunits, which may
or may not correspond to individual proteins, are
called capsomers. The capsid encloses
the genetic material of the virus.
These viruses appear spherical in shape, but a closer
look actually reveals they are icosahedral. The
icosahedron is made up of equilateral triangles fused
together in a spherical shape. This is the most optimal
way of forming a closed shell using identical protein
sub-units. The genetic material is fully enclosed inside
of the capsid. Viruses with icosahedral structures are
released into the environment when the cell dies,
breaks down and lyses, thus releasing the virions.
Examples of viruses with an icosahedral structure are
the poliovirus, rhinovirus, and adenovirus.
What are serotypes
Serotype or serovar are distinct variations within a species of
bacteria or viruses or among immune cells of different individuals.
These microorganisms, viruses, or cells are classified together
based on their cell surface antigens, allowing the epidemiologic
classification of organisms to the sub-species level.
There are tree serotypes of poliovirus with common antigen. They
have identical properties and their genomic base sequences share
36-52% homology. Poliovirus show marked antigenic stability.
TRANSMISSION OF POLIOVIRUS
Poliomyelitis caused by poliovirus usually occurs
in summer. When a person is infected with
poliovirus, the virus resides in the intestinal tract
and mucus in the nose and throat. Poliovirus
transmission most often occurs through contact
with stool of this infected person (known as fecal-
oral transmission). Less frequently, polio
transmission can occur through contact with
infected respiratory secretions or saliva (oral-oral
Signs and symptoms, which generally last one to
10 days, include:
Back pain or stiffness
Neck pain or stiffness
Pain or stiffness in the arms or legs
Muscle weakness or tenderness
Poliovirus replicates in cells of human
gastrointestinal tract and is excreted in feces. In
rare cases it invades Central Nervous
System(CNS) and causes paralytic disease called
poliomyelitis. Incubation period is 7 to 14 days.
Following ingestion, The virus multiplies in
oropharyngeal and intestinal mucosa. The
lymphatic system, in particular, the tonsils and
payer’s patch of the ileum is invaded. The virus
enters the blood resulting in viremia.
TREATMENT AND PREVENTION
Active immunization can cure Polio. There are two
vaccines available; Inactivated Salk Vaccine and
Attenuated Sabin Vaccine.
The former, also called formalin inactivated
Intramuscular Polio Vaccine (IPV),was developed
by Jonas Salk. It contains an injected dose of three
antigenic strains of killed polio virus.
The later, also called Oral Polio Vaccine(OPV),was
developed by Albert Sabin. It contains attenuated
forms of poliovirus.
Somnath Dutta,2010,Textbook of Virology,
Adhyayan Publishers and Distributors, New Delhi.
Fritz H. Kayser, Kurt A. Bienz, Johannes Eckert,
Rolf M. zinkernagel,2005,Medical Microbiology,
Thiem, New York.