Poliovirus: Introduction, Common Properties, Pathogenesis, Lab Diagnosis, Treatment and Prevention

achaurasiya

5 years ago

Poliovirus: Introduction, Common Properties, Pathogenesis, Lab Diagnosis, Treatment and Prevention

Introduction of Poliovirus

Poliovirus belongs to the family Picornaviridae and it is a small RNA virus.

Common properties of Picornaviridae

20 -30 nm diameter
Capsid: 60 capsomeres arrange in icosahedral symmetry
Does not contain envelop
Contains single-stranded RNA
Most of the members grow in tissue culture

Two important genera that can infect humans are-

Genus Species

Enterovirus poliovirus

Rhinovirus Rhinovirus

Poliovirus

It causes a disease called poliomyelitis. It is an infection of a neurotropic enterovirus. Poliovirus that causes paralysis through motor neuron destruction and muscle weakness and muscle atrophy ( wastage of muscles)

Morphology of Virus

22-30nm
SSRNA
Capsid -60 capsomers each consisting of four viral proteins ( VPI-1 VP4) with icosahedral symmetry – hexagonal in shape.
Does not contain envelop

Resistance

Inactivated at 55 °C for 30 minutes. Magnesium chloride (MgCl2) prevents heat activation and also by milk and ice cream
Resistances to Chloroform, Ether, Proteolytic enzymes, and Bile and Detergents.
Stable at pH 3.
In feces, it can survive:

At 4°C for a month.
At room temperature for 1 day to weeks
At -20°C for years.

5. Formaldehyde and oxidizing disinfectants can destroy Poliovirus

6. Pasteurization destroys the virus

7. Chlorination destroys the virus.

8. Poliovirus does not survive in lyophilization

9. Phenolic disinfectants are not effective

Serotyping

On the basis of the neutralization test, poliovirus is of three serotypes. Poliovirus serotype 1 is the most common and virulent type. It is repeated isolated from patients with poliomyelitis and causes epidemics. Serotype 2 is usually associated with endemic infection while serotype 3 causes occasional endemic infection.

Pathogenesis of Poliovirus

The mode of transmission is feco -oral route. Site of multiplication: Lymphatic tissues of the oropharynx and epithelial cells of the intestine. Site of dissemination: spinal cord and brain through viremia ( alternative pathway may be via entry into motor neurons at peripheral neuromuscular junction). Virus multiples in the neurons of the central nervous system( CNS ) and destroy anterior horn cells of the spinal cord. Children below 5 years are most susceptible to poliovirus.

Clinical Feature

Inapparent infection
Mild illness
Aseptic meningitis
Paralytic poliomyelitis

Laboratory Diagnosis of Poliovirus

Specimen: The common samples are nasal secretion, fecal specimen, throat swab, and CSF.

For isolation of the virus

Pharyngeal aspirates
Feces

Direct demonstration of the virus

Electron microscopy

Culture

Monkey kidney cell line, Human amnion, HeLa, Hep-2, Buffalo green monkey (BGM), MRC-5 cell line
CPE is observed in 3-4 days

Antibody detection: ELISA, complement fixation test

Neutralization Test: For antigen detection

Neutralization with the use of standard antisera pf Poliovirus type 1, 2,3

Antigen

There 3 antigen types

Type: 1, 2,3

Each type has type-specific antigen C ( coreless) and D ( dense)

D antigen ( also called Native or N antigen ) is associated with the whole virion and is type-specific.

C antigen of all types is cross-reactive. It is also called heated or H antigen because the D antigen is converted into the C antigen by heating the virus at 56°C.

One attack of poliomyelitis gives permanent immunity only against the type causing the infection.

Molecular diagnosis: PCR

Treatment

There is no antiviral drug to treat the poliovirus.

Preventive Measures

Use of Vaccine

Live Attenuated Oral Polio Vaccine ( OPV): It was prepared using poliovirus type 1, 2,3 by growing into a primary monkey or human diploid cell lines and stabilize by MgCl2. It is developed by Albert Sabin in 1962 and contains a live attenuated strain of all serotypes. The vaccine is given orally at 2 months of age simultaneously with the first DP and it is recommended for all children below 5 years. In endemic countries monovalent oral poliovirus type I vaccine (MOPvI) is introduced to eliminate the last reservoir of poliovirus.
Salk’s Killed Polio Vaccine ( SALK 1953): Formalized strains of this virus type 1, 2, 3 separately and mixed together. It was prepared by Jonas Salk in 1956 which is also known as inactivated poliovirus vaccine (IPV). The vaccine is given intra- muscularly at the age of 6 months and 2nd and 3rd dose at 4-6 weeks interval. The fourth (booster) dose is given 6 months after 3rd dose. It is effective against all serotypes of this virus.

Adopting proper sanitation
Use of safe drinking water

Epidemiology

WHO documented Polio cases have reduced by over 99% since 1988, from an estimated 350 000 cases in more than 125 endemic countries then, to 37 reported cases in 2016. Among 37 cases, only 3 strains of wild poliovirus (type 1, type 2, and type 3). Wild poliovirus type 2 was eradicated in 1999 and no case of wild poliovirus type 3 has been found since the last reported case in Nigeria in November 2012. Poliovirus endemic countries are Pakistan, Afghanistan, and Nigeria.

Keynotes

Special features OPV

Offers protection against all serotypes 1,2,3.
Includes production of IgM and both secretory and circulatory IgA.
Given orally for active immunization at the age of 2 months and 2nd and 3rd dose at 2 months interval. The fourth dose is given at 1.5 years of age.
Economy: Much cheaper than the killed vaccine.
Essay to administer in mass immunization
The attenuated live viruses can multiply in the cells of the intestine thus progeny viruses are disseminated in the community through the fecal route. Which contributes to indirect immunization.
Poliovirus infection due to living vaccines cannot establish when the alimentary tract has already been infected by another enterovirus due to biological interference.

Improved sanitation and an effective immunization program would help to eradicate poliomyelitis in the whole world.
Incubation period: is 9 to 12 days.
Human is only natural host for this virus.