Poliovirus: Characteristics, Epidemiology, Serotypes, Mode of transmission, Pathogenesis, Clinical manifestation, laboratory diagnosis, Prevention and control

Characteristics of Poliovirus

Poliovirus can survive for 4-6 months in cold water.
It can be inactivated by pasteurization temperature, 0.3% formaldehyde, 0.1M HCL, residual cholorine of (0.3-0.5) ppm
It is resistant to lipid soluble agents such as Ether, Chloroform, bile and proteolytic enzymes of intestine
It can survive in faeces for months at 4° C and for years at -20°

WHO recorded Polio cases have decreased by over 99% since 1988, from an estimated 350 000 cases in more than 125 endemic countries then, to 37 reported cases in 2016.
Of the 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.
Pakistan , Afghanistan and Nigeria are endemic to poliovirus

On the basis of neutralization test poliovirus is divided into three serotypes.

Poliovirus 1: it is most common and virulent type. It is frequent isolated from patients with poliomyelitis and causes epidemics
poliovirus 2: it is usually associated with endemic infection
poliovirus 3: it causes occasional endemic infection

Human are only natural host for Poliovirus
primarily by: Faeco-oral route by Ingestion of virus contaminated food and water
Droplet infection, inhalation

in oropharynx and intestinal epithelium
Incubation period: 9-12 days
Virus regularly present in throat and in stool of patient before clinical symptoms

Virus enter the lymphatic and blood from oropharynx and intestinal epithelium producing primary viremia
In most of the case, primary viremia is cleared by host defense. But in children who fail to control primary viremia develop Poliomyelitis.

When primary viremia is not controlled then there is a secondary viremia
After multiplication in reticuloendothelial syetem, it envades the blood stream again causing major or secondary viremia.
During secondary viremia, virus crosses the blood-brain barrier and gain access to brain and spinal cord.
Virus multiply in nerve cell of CNS and damage anterior horn of spinal cord as well as nerve cell of medulla oblongata, pons etc. therefore patients suffer from neurological symptoms

Few suffer from minor illness, very few suffer from meningitis and less than 1% suffer from major paralytic disease

6. Death is rare. And if occur it is due to respiratory paralysis

Specimen: nasal secretion, faecal samples, throat swab, CSF

Electron Microscopy: virus detection
Virus isolation: culture on monkey kidney cell line, Human amnion, HeLA, Hep-2, Buffalo green monkey (BGM), MRC-5 cell line
Antibody detection: ELISA, complement fixation test
Antigen detection: neutralization test
Molecular diagnosis: PCR

Developed by Albert Sabin in 1962
Contains live attenuated strain of all serotypes of poliovirus
It is administered Orally at 2 months of age simultaneously with first DPT
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