Epidemiology of poliomyelitis and strategy for eradication
By Sanjay GeorgeEPIDEMIOLOGY OF POLIOMYELITISAND 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, Afghanistanand 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 infectedperson.• Period of Communicability – 7 to 10 days before and after onset ofsymptoms. In feces virus excreted for 2 to 3 weeks sometimes aslong as 3 to 4 months.• Incubation Period – 7 to 14 days.
HOST FACTORS• Age: Children most susceptible. 6months to3years most vulnerable• Sex• Risk Factors• Immunity
ENVIRONMENTAL FACTORS• More common during rainy season• Environmental Sources – Contaminatedfood, water and flies• Overcrowding and poor sanitation contribute tospread 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, sorethroat, 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 inswallowing, weakness or loss of voice.• Respiratory insufficiency can lead to death
PREVENTION• Immunization is the sole effective method tocontrol 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 32units of type – 3 D antigen.• IM route• 1st 3 doses given at interval of 1 - 2 months and fourth dose 6 – 12months 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, 1,00,000TCID 50 of type 2 virus and over 3,00,00 TCID 50 of type 3virus.• Dose : 2 drops• National Immunization Programme : recommendsprimary 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 virustype 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 allpersons over 6 weeks of age who have not beenpreviously immunized or immune status is unknown.
STRATEGIES FOR ERADICATION ININDIA• Pulse Polio Immunization Days• High levels of immunization coverage• Monitor OPV coverage at district level and below• Improved surveillance capable of detecting all cases ofAFP• Rapid case investigation• Arrange follow up at 60 days• Conduct outbreak control for confirmed or suspectedcases
LINE LISTING OF CASES• Started in 1989 to check for duplication, year of onset ofillness, identification of high risk pocket groups and documentationof high risk age groups• All cases of AFP should be reported to chief medical officer/districtimmunization 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 riskdistricts where wild polio virus is present.
PULSE POLIO IMMUNIZATION• Refers to sudden, simultaneous, mass administration of OPVon a single day to all children 0 – 5 years of age regardless ofprior immunization status.• It occurs as 2 rounds about 4 – 6 weeks apart during lowtransmission 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 caseof 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 populationlike highly migrant laborers• - Short Interval Additional Dose• - Monitoring of SIA coverage• - Expanded environmental sampling
WHO STRATEGIES CONTD.• - Serological surveys to document program status, assessprospects and adjust plans accordingly by moreaccurately determining population immunity.• - Enhanced AFP surveillance• - Enhance communication/social mobilization in priorityareas• - Rehabilitation of Polio affected individuals