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 groupsChildren are more susceptible than adultsMost 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:a) Inapparent (subclinical) infectionb) Abortive polio or minor illnessc) Non paralytic poliod) 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• Recognized only by virus isolation or rising

antibody titres

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:

a) Inactivated polio vaccine(IPV)/ Salk

b) 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:

a) Immunity is not rapidly achieved, more than one dose required to induce immunity

b) 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 yrs2

11

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:

1. Easy to administer2. Doesn't require highly trained personnel3. Induce both humoral and intestinal

immunity4. Even single dose elicits substantial

immunity5. Herd immunity6. Useful in controlling epidemics7. 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

IPV(Salk)1. Killed virus2. Given s/c or i/m3. Only humoral

immunity, no local immunity

4. More difficult to manufacture

OPV(Sabin)5. Live attenuated6. Orally7. Both humoral &

intestinal immunity

8. Easy to manufacture

IPV5. Prevent paralysis, but

do not prevent re-infection with wild polio

6. Not useful in epidemics

7. Virus content is 10,000 times more than OPV, Costlier

8. Doesn't require stringent condition during storage & transportation

OPV9. Prevent paralysis and

also intestinal re-infection

10. Can be used in epidemics

11. Cheaper

12. Required to be stored & transported in sub zero temperature

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