POLIOMYELITIS

AGENT FACTORS: Agent: Poliovirus, - RNA virus, serotype –1,2,3 - Most outbreaks – type 1 -Survive for long periods in external environment in cold climate - Can live in water for 4 mnths & faeces for 6 mnths - hence faecal – oral route

Reservoir of infection: Man is the only known reservoir Most are subclinical cases, no chronic carrier, no animal carriers Mild & subclinical cases plays an important role in spread of infection Submerged part in iceberg phenomenon For every clinical case- 1000 children and 75 adult subclinical cases

Infectious material: Faeces and Oro-pharyngeal secretions of an infected person Period of communicability: Cases are most infectious 7 to 10 days before and after onset of symptoms In faeces the virus is excreted for 2 to 3 wks & can go on for as long as 3 – 4 mnth

HOST FACTORS: Age: occur in all age groups Children are more susceptible than adults Most vulnerable age is between 6 months to 3 years in India Sex: M:F, 3:1

Risk factors: Paralytic polio in an individual who have been already infected with polio virus, has been found to precipitated by factors like - fatigue, trauma, intra muscular injections, operative procedures esp. during epidemics of polio, immunizing agents particularly alum containing DPT

Immunity: Infection with one type does not offer complete protection against other two type of viruses Neutralizing Ab’s - index of immunity to polio after infection Environmental factors: More seen to occur in rainy season Sources are contaminated water, food, flies Overcrowding and poor sanitation provides opportunities for exposure to infection

Mode of transmission: Faecal-oral route – developing countries Droplet infection – developed countries, acute phase of disease Incubation period: 7-14 days(range 3-35 days) Clinical spectrum: Inapparent (subclinical) infection Abortive polio or minor illness Non paralytic polio Paralytic polio

a) Inapparent (subclinical) infection: Occurs in approx. 91-96% infections No symptoms Recognized only by virus isolation or rising antibody titres b) Abortive polio or minor illness: Occurs in 4-8% of infections Causes only mild or self limiting illness Patient recovers quickly

c) Non paralytic polio: Occurs in 1% of all cases s/o: stiffness and pain in neck and back Disease lasts 2 to 10 days Recovery is rapid It is synonymous to aseptic meningitis

d) Paralytic polio: Occurs in less than 1% cases Invades CNS & causes paralysis of varying degree Predominant sign – Asymmetrical flaccid paralysis (AFP) If fever at time of onset of paralysis – polio suspected Other symptoms - malaise, anorexia, nausea, vomiting, abdominal pain, sore throat, head ache and constipation

Signs: stiffness of neck & back muscles Tripod sign Descending paralysis – hip to downwards Asymmetrical patchy paralysis DTRs are diminished before onset of paralysis Progression of paralysis to reach its maximum in majority cases occurs in less than 4 days No sign of sensory loss

Cranial nerve involvement seen in bulbar and bulbo spinal forms of paralytic polio Facial asymmetry, difficulty in swallowing, weakness of voice Respiratory insufficiency can be life threatening & is usually cause of death Atrophy of muscles also seen Progressive paralysis, coma & convulsions indicate diagnosis other than polio Treatment: No specific treatment Physiotherapy and good nursing care from beginning can minimize/ prevent crippling

Prevention: Immunization is the most effective method Two types of vaccine: Inactivated polio vaccine(IPV)/ Salk Oral polio vaccine(OPV)/ Sabin

Inactivated polio vaccine(IPV)/ Salk: Given i/m (preferred) or s/c injection Stable at ambient temperature, but should be refrigerated to ensure no loss of potency Freezing should be avoided Primary course of immunization consist of 4 inoculations Available as stand alone product or in combination form Induces humoral antibody and not intestinal/ local immunity

IPV protect individual from paralytic polio, but do not prevent re-infection of gut by wild polio viruses Hence it does not offer any benefit for the community as wild virus can multiply in gut and be a source of infection to others It is unsuitable during epidemic because: Immunity is not rapidly achieved, more than one dose required to induce immunity Injections are to be avoided during epidemics as they may precipitate paralysis

Advantages: Can be given in immuno compromised and pregnant women Associated risks: No serious ADRs except minor local erythema, induration and tenderness

Oral polio vaccine(OPV)/ Sabin: Described by Albert Sabin in 1957 Contains live attenuated vaccine (type 1,2,3) National immunization schedule: Primary course of 3 doses at 1 month interval Starting at 6 wks and followed by 10 & 14 wks Zero dose is recommended at birth All infants should vaccination before 6 months of age as most polio cases occur between 6 months to 3 years period One booster dose of OPV is given at yrs

Dose & mode: 2 drops, orally Development of immunity: IgA produced in intestine prevent subsequent infection of alimentary canal with wild polio, thus preventing spread in community OPV induces both local & systemic immunity Vaccine progeny excreted in faeces 2* spread to household contact & susceptible host in community Herd immunity established This property eliminates wild polio from the community & replace it with attenuated strain

Advantages: Easy to administer Doesn't require highly trained personnel Induce both humoral and intestinal immunity Even single dose elicits substantial immunity Herd immunity Useful in controlling epidemics Relatively inexpensive

Complications: VAPP(vaccine associated paralytic poliomyelitis)----due to type 3 strain Containdications: All live vaccines are C/I in immuno compromised patients and pregnant women IPV given in immuno compromised if necessary

Storage: A) stabilized vaccine – recent vaccines are heat stabilized by adding magnesium chloride in it Can be kept for a year at 4* C & for a month at 25*C with out loosing potency B) Non stabilized vaccine – Vaccine sould be stored at -25*C in deep freezer Vaccine vial kept in ice at field level during administration to children

Sequential administration of IPV & OPV: In some countries sequential schedule of 1 – 2 dose of IPV followed by > 2 doses of OPV has been adopted This approach reduce the event or even prevent VAPP, while giving both systemic and local immunity

Differences between IPV & OPV OPV(Sabin) IPV(Salk) Killed virus Live attenuated Given s/c or i/m Orally Only humoral immunity, no local immunity Both humoral & intestinal immunity More difficult to manufacture Easy to manufacture

IPV OPV Prevent paralysis and also intestinal re- infection Prevent paralysis, but do not prevent re- infection with wild polio Not useful in epidemics Can be used in epidemics Virus content is 10,000 times more than OPV, Costlier Cheaper Doesn't require stringent condition during storage & transportation Required to be stored & transported in sub zero temperature

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