By Sanjay George

EPIDEMIOLOGY OF POLIOMYELITIS AND STRATEGY FOR ERADICATION

INTRODUCTION• Pre-vaccination era : Polio was worldwide

• 1988 : World Health Assembly resolved to eradicate Polio

• 1988 : 125 endemic countries

• 2008 : 4 endemic countries – India, Pakistan, Afghanistan and Nigeria

• Last reported case in India was 0n 13th January 2011.

CAUSATIVE AGENT• Poliovirus – Enterovirus (RNA virus) belonging to Picornaviridae

• Serotypes – 1,2,3 (most outbreaks due to type-1)

• Mode of Transmission – Feco-oral Route & Droplet Infection

• Reservoir of Infection – Man

• Infectious Material – Feces and oro-pharyngeal secretion of infected person.

• Period of Communicability – 7 to 10 days before and after onset of symptoms. In feces virus excreted for 2 to 3 weeks sometimes as long as 3 to 4 months.

• Incubation Period – 7 to 14 days.

HOST FACTORS• Age: Children most susceptible. 6months to

3years most vulnerable

• Sex

• Risk Factors

• Immunity

ENVIRONMENTAL FACTORS• More common during rainy season

• Environmental Sources – Contaminated food, water and flies

• Overcrowding and poor sanitation contribute to spread of infection.

CLINICAL SPECTRUM• Unapparent (Subclinical) Infection : 91 – 96%

• Abortive Polio or Minor Illness : 4 – 8%

• Non-Paralytic Polio : 1%

• Paralytic Polio : Less than 1%

PARALYTIC POLIO• Less than 1% of infections.

• Virus invades CNS causing various degrees of paralysis

• Asymmetrical flaccid paralysis

• H/O fever at time of onset of paralysis indicative of Polio

• Malaise, anorexia, vomiting, headache, sore throat, constipation, abdominal pain

• Signs of meningeal irritation

• Tripod Sign may be present

PARALYTIC POLIO CONTD.• Descending paralysis

• No sensory loss

• Cranial nerves maybe involved

• There maybe facial asymmetry, difficulty in swallowing, weakness or loss of voice.

• Respiratory insufficiency can lead to death

PREVENTION• Immunization is the sole effective method to

control Polio.

• 2 types of vaccines are available:

• - Inactivated (Salk) polio vaccine

• - Oral (Sabin) polio vaccine

IPV• Vaccine contains 40 units of type -1 antigen. 8 units of type – 2 and 32

units of type – 3 D antigen.

• IM route

• 1st 3 doses given at interval of 1 - 2 months and fourth dose 6 – 12 months after the third dose.

• First dose : 6 weeks

• Drawback:

• No benefit to community

• Immunity not rapidly achieved

• Shouldn’t be administered during epidemic

• Advantages

• Safer vaccine

OPV• Live attenuated vaccine, Trivalent vaccine

• Contains 3,00,00 TCID 50 of type 1 poliovirus, 1,00,000 TCID 50 of type 2 virus and over 3,00,00 TCID 50 of type 3 virus.

• Dose : 2 drops

• National Immunization Programme : recommends primary course of 3 doses at 1 month intervals

• First dose at 6 weeks.

EPIDEMIOLOGICAL INVESTIGATIONS• Immediate epidemiological investigation.

• Epidemic: 2 or more local cases caused by the same virus type in a 4 week period.

• Feces samples forwarded to lab

• Paired sera should be collected.

• WHO should be notified

• Within epidemic area OPV should be provide for all persons over 6 weeks of age who have not been previously immunized or immune status is unknown.

STRATEGIES FOR ERADICATION IN INDIA• Pulse Polio Immunization Days

• High levels of immunization coverage

• Monitor OPV coverage at district level and below

• Improved surveillance capable of detecting all cases of AFP

• Rapid case investigation

• Arrange follow up at 60 days

• Conduct outbreak control for confirmed or suspected cases

LINE LISTING OF CASES• Started in 1989 to check for duplication, year of onset of illness,

identification of high risk pocket groups and documentation of high risk age groups

• All cases of AFP should be reported to chief medical officer/district immunization officer with following details

• Name, age and sex of patient

• - Father’s name and complete address

• - Vaccination Status

• - Date of onset of paralysis and date of reporting

• - Clinical Diagnosis

• - Doctor’s name, address and phone number

MOPPING UP• Last stage in polio eradication

• Involves door to door immunization in high risk districts where wild polio virus is present.

PULSE POLIO IMMUNIZATION• Refers to sudden, simultaneous, mass administration of OPV

on a single day to all children 0 – 5 years of age regardless of prior immunization status.

• It occurs as 2 rounds about 4 – 6 weeks apart during low transmission season of Polio, i.e.. Between November – February

• Doses of OPV in PPIs are extra doses

• Children should receive scheduled doses as well as PPI doses.

• No minimum interval between scheduled dose and PPI dose

• Vaccines use vial monitors

AFP SURVEILLANCE• PPI supported by AFP surveillance

• Conducted by network of surveillance medical officers

• SMOs are located at state HQs and regional places in case of larger states.

• Regular weekly reporting system

WHO STRATEGIES• Global Polio Eradication Initiative

• - Use of Bivalent OPVs

• - State/district/block specific plans for endemic and re- established transmission areas

• - Special teams and tactics for under served population like highly migrant laborers

• - Short Interval Additional Dose

• - Monitoring of SIA coverage

• - Expanded environmental sampling

WHO STRATEGIES CONTD.• - Serological surveys to document program status, assess

prospects and adjust plans accordingly by more accurately determining population immunity.

• - Enhanced AFP surveillance

• - Enhance communication/social mobilization in priority areas

• - Rehabilitation of Polio affected individuals

THANK YOU