Poliovirus - Morphology, Cultivation, Pathogenicity Clinical Features & LD...

POLIOVIRUS – MORPHOLOGY, RESISTANCE, ANTIGENIC PROPERTIES, CULTIVATION, PATHOGENICITY, CLINICAL FEATURES & LABORATORY DIAGNOSIS

INTRODUCTION TO POLIOVIRUS

Poliovirus is the causative agent of poliomyelitis, an acute infection that affects the CNS i.e. the brain and spinal cord.

MORPHOLOGY OF POLIOVIRUS

Polio virus belongs to Enterovirus genus of Picornaviridae

Polio virus is a Spherical, Enveloped virus, composed of 60 subunits, each consisting of four viral Proteins – VP1 – VP4, arranged in icosahedral symmetry.

Size: 27-30 nm.

Genetic material – ssRNA.




RESISTANCE SHOWN BY POLIOVIRUS

Polio virus is resistant to Ether, Chloroform, Bile, Proteolytic enzymes & detergent, is Stable at pH 3.

In feces, it can survive for months at 4oC and for years at -20oC, readily inactivated by heat – 55oC for 30 minutes.

Polio virus doesn’t survive lyophilization well.

ANTIGENIC PROPERTIES OF POLIOVIRUS

By neutralization test, Polio virus strains have been classified into three types as: 1, 2 & 3.

Type 1 is the most common and causes most epidemics. Type 2 usually causes endemic infections. Type 3 strains have caused epidemics.

HOST RANGE & CULTIVATION OF POLIOVIRUS

Natural infection occurs only in humans. Experimental host is monkey, may be infected by intracerebral or intraspinal inoculation.

Polio virus grows readily in primary monkey kidney cultures, Vero, HeLa and Hep-2 cell lines, used for diagnostic cultures and vaccine production.

PATHOGENICITY OF POLIOVIRUS

Mode of Transmission: Polio virus is transmitted primarily by Fecal-Oral route through ingestion, other routes includes Inhalation & conjunctiva.

Initially virus multiplies in epithelial cells of GIT &

Lymphatic tissues, from the tonsils

Spreads to regional lymph nodes- enters bloodstream.

Carried to the spinal cord & brain.

In CNS, virus multiplies in neurons & destroys them and

Degenerates the Nissl Bodies.

Lesions are mostly in anterior horn of spinal cord, cause paralysis.

CLINICAL FEATURES OF POLIOVIRUS INFECTION

The incubation period ranges 4 days to 4 weeks; average 10 days.

Minor illness characterized by primary viremia – Fever, Headache, Sore throat and malaise lasts for 1-5 days.

Major illness, following minor illness after 3-4 days, characterized by Fever, Headache, Stiff neck – marks the stage of viral invasion of CNS, proceeding to paralytic poliomyelitis, flaccid paralysis develops.

LABORATORY DIAGNOSIS OF POLIOVIRUS

⇒ Specimen : Blood, CSF, Throat swab and Feces; autopsy specimen includes brain & spinal cord.

⇒ Direct demonstration of virus : virus can be demonstrated in feces y direct electron microscopy or by immune electron microscopy.

⇒ Isolation of virus : specimens are inoculated into HeLa and Hep-2 cell line, virus growth indicated by typical cytopathic effect seen in cells within 2-3 days.

⇒ Serology : Complement Fixation Test and neutralization test can be used for serotyping of poliovirus.

PROPHYLAXIS OF POLIOVIRUS

Both active and passive immunization is available but passive immunization by administration of human gamma globulins is of little value

Active immunization by vaccination is effective against poliovirus; two types of vaccines are available, killed polio vaccine (Salk) and Live attenuated oral polio vaccine (Sabin).

The Salk vaccine is given by deep subcutaneous or intramuscular injection, induces only systemic antibody response but do not provide intestinal or mucosal immunity.

The Sabin vaccine administered orally, commonly called as oral polio vaccine (OPV), induces both local secretory IgA antibodies in the intestine or mucosa and also humoral antibodies (IgM & IgG).

SAHIL BATRA

Hi, I'm the Founder and Developer of Paramedics World, a blog truly devoted to Paramedics. I am a Medical Lab Tech, a Web Developer and Bibliophiliac. My greatest hobby is to teach and motivate other peoples to do whatever they wanna do in life.

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