Download - 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