POLIO VIRUS

By-

Poornima R.

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.

Icosahedral structureThese 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 serotypesSerotype 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

transmission).

SYMPTOMS

Signs and symptoms, which generally last one to 10 days, include:

Fever

Sore throat

Headache

Vomiting

Fatigue

Back pain or stiffness

Neck pain or stiffness

Pain or stiffness in the arms or legs

Muscle weakness or tenderness

Meningitis

PATHOGENESIS

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.

REFERENCE

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.

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