Poliomyelitis: Pathogenesis, clinical features and Laboratory diagnosis

Poliomyelitis is a contagious disease which spreads through person to person contact (the virus infects only human) mainly via fecal oral route. The virus affects the young children (mainly children under 5 years of age) and can cause permanent disability.  Polio virus has been eradicated from most of countries of the world but still 2 countries, Pakistan and Afghanistan are endemic. Vaccination is the best way to protect people and stop transmission of Poliomyelitis. There are two types of vaccine; inactivated poliovirus vaccine (IPV) and oral poliovirus vaccine (OPV).

POLIOMYELITIS
– destruction of motor neurons in spinal cord → flaccid paralysis
–         very restricted host range → natural infection occurs only in humans.
–         Grows readily in tissue cultures of primate origin.
 PATHOGENESIS–         transmitted by faeco- oral route.
–         Virus multiplies initially in epithelial cells of AC (Oropharynx or intestine) and the lymphatic tissue ( tonsils / payers patches).
–         Regularly present in throat and stools before the onset of illness.
–         Then spreads to the regional lymph nodes and enters blood stream (minor / 20 viraemia) across the BBB.
–         Direct neural transmission may also occur eg after tonsillectomy..
–         In the CNS, Virus multiplies selectively in the neurons destroys the anterior horn cells of spinal cord.
–         Earliest change is degeneration of Nissils bodies.
–         When degeneration becomes irreversible, necrotic cell lyses or is phagocytosed.
–         Viruses don’t multiply in muscle in vivo.
–         Changes that occur in peripheral nerves and voluntary muscles are secondary to destruction of nerve cells.
Clinical findings
–         Incubation period 7-14 days.
–         Inapparent infection: 90-95% cases; only seroconversion.
–         Abortive poliomyelitis: 4-8%; minor illness.
– Fever, malaise, drowsiness, headache, nausea, vomiting, constipation.
Recovery in few days.
–         Non- paralytic poliomyelitis ( aseptic meningitis) – 1-2%
– above symptoms + stiffness and pain in back and neck; 2-10 days.
–         Paralytic poliomyelitis: 0.1-2%
– flaccid paralysis resulting from lower motor neuron damage.
– Maximal recovery with in 6 months, with residual paralysis lasting much longer.
–         Progressive post – poliomyelitis muscle atrophy: rare
– recrudescence of paralysis and muscle wasting.
– Decades after experience with paralytic poliomyelitis.
– doesn’t appear to be a consequence of persistent infection rather a result of physiologic and aging changes.
Lab diagnosis
specimen: throat swabs, rectal swabs / stool, blood, CSF ( uncommon).
No permanent carriers known.
Specimen should be kept frozen during transmit to lab.
A. Isolation of virus.
– can be isolated from blood and pharyngeal aspiration during 10 viraemia,(3-5 days after infection). From feces → upto 5 weeks.
–         After processing specimen, inoculated into tissue culture.
      •Primary monkey kidney cells, typical CPE in 2-3 days.
       • Identification by neutralization tests with pooled and specific antisera.
–         Virus isolation from feces must be interpreted along with clinical and serological evidence.
B. direct demonstration of virus by electron microscopy
c. serology: less often employed.
– paired serum specimens to show a rise in antibody titer
–         Only 1st infection produces strictly type- specific responses.
About tankeshwar 385 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion, I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.

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