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 4^oC and for years at -20^oC, readily inactivated by heat – 55^oC 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.