polio and rabies viruses

Microbiology
Poliovirus: Dr.Jawad K. AL-Khafaji
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General properties:
• It belongs to family picornaviridae
• It is spherical shape.
• Nucleocapsid is icosahedral .
• Genome is ssRNA
• Non-enveloped

There are three serotypes; poliovirus type-1is most common and it causes most epidemics , poliovirus type-2 is usually associated with epidemics, poliovirus type-3 occasionally cause epidemics

Sources and transmission:
The infection naturally occurs only on humans. It is transmitted by fecal-oral route by ingestion of food and water contaminated with human feces. The virus considered as enterovirus . poliovirus cause poliomyelitis . Most cases occur in children.

Pathogenesis:
Virion interacts with specific cell receptor on the cell membrane and then enters the cell. After replicating in oropharynx(also in tonsils and in LN of neck) and small intestine tract, especially in lymphoid tissues , the virus spread through blood stream(or axon of peripheral nerves) to CNS, then attacking motor neurons located in anterior horn of spinal cord .
Death of infected cells results in paralysis of muscles innervated by those neurons. The virus also affects the brain stem, leading to bulbar poliomyelitis with respiratory paralysis.

C/F:
Ip (10-14 days) Poliovirus causes direct pathological changes in CNS and is responsible for causing symptoms of the poliomyelitis disease. Most cases 95% are asymptomatic(no illness), 4% minor illness(abortive infection) with fever, headache , nausea, drowsiness, vomiting and sore throat, 1% major illness with or without paralysis . The non-paralytic poliomyelitis is characterized with fever, stiff neck, malaise, while paralytic poliomyelitis is characterized by flaccid paralysis occurs especially in lower limbs such as legs. Respiratory paralysis can occur if brain stem is infected.