Poliomyelitis

Epidemiology & Control of poliomyelitis

poliomyelitis

Reservoir of infectionHumans Mode of transmission person – to – person (direct faeco – oral route) Ingestion of contaminated water & food. Pharyngeal spread (air borne) in areas where sanitation is good.

Incubation period 3 – 21 days ( average 10 days)Clinical featuresThe disease may take one of the following forms:Inapparent infection ( Asymptomatic infection) in more than 90% of cases. Non-paralytic febrile illness (Non specific fever).

Aseptic meningitis ( non paralytic poliomyelitis) in about 1% of the cases. Paralytic poliomyelitis in less than 1%.SymptomsFever, malaise, headache, nausea & vomiting.if the disease progress, stiffness of the neck with or without paralysis .Case fatality for paralytic cases is 2 – 10 %, it increases with age.

Factors which determine the development of paralytic poliomyelitis

The state of immunity of the affected individual Trauma , excessive fatigue, pregnancy, and intramuscular injection during the period of acute febrile illness may precipitate paralysis Tonsillectomy increases the risk of paralysis

Characteristics of the paralysis

Asymmetrical with fever present at the onset. The site of paralysis depends on the location of nerve cell destruction in the spinal cord or brain stem. The legs are affected more often than the arms. Paralysis of the respiratory muscles lead to death.

Diagnosis

Clinical features. Isolation of the virus from stool, CSF or nasopharyngeal secretions (cell culture). Detection of type specific antibodies.

Period of communicability

The virus is detected in throat secretions 36 hours after infection& in stool 72 hours after infection in both clinical & in asymptomatic cases.The virus persists in the throat for one week and in the stool for 3 – 6 weeks.Cases are most infectious during the few days before & the few days after onset of symptoms.

Epidemiology

Poliomyelitis is about to be eradicated worldwide. The disease has been eradicated in the western hemisphere. The disease is now limited to few developing countries . -The disease primarily affects children below 3 years of age.

Control

General Preventive measures: Sanitary disposal of human excreta Health education to raise the standards of personal hygiene Specific preventive measures: Measures for Patients: Notification is very important Isolation of the patient is desirable


Disinfection and safe disposal of patients faeces and pharyngeal discharges Treatment of patients Measures for Contacts: Surveillance of contacts for 3 weeks from their last contact with the patient Vaccination with OPV Tonsillectomy & dental extraction should be postponed when poliomyelitis epidemic is present and injections of any kind reduced to the minimum Avoid over-exertion such as games and swimming.

Vaccination is the most effective method of preventing poliomyelitis. Two types of polio vaccines are available:1- Oral Polio Vaccine (OPV) or Sabin Vaccine: trivalent live attenuated vaccine. It contains all the three viruses 3 doses are required at 6 – 8 weeks interval Induces both circulating antibodies & intestinal immunity Vaccination


2- Injectable Polio Vaccine (IPV) or Salk Vaccine: injectable, inactivated poliovaccine.It contains all three polio viruses 3 doses are required. First 2 doses are given at 1 – 2 months interval 3rd dose 6 – 12 months after the 2nd . Mainly induces circulating antibodies

WHO recommends the use of OPV because: 1- low cost 2- Ease of administration 3- Capacity to provide population immunity (immunizes some susceptible contacts through secondary spread).

Disadvantages of OPV

unstable especially in tropical climates Interference by other enteric viruses May cause paralytic poliomyelitis Vaccine-Associated paralytic poliomyelitis (VAPP).


Vaccine-Associated paralytic Poliomyelitis = VAPP The occurrence of clinical paralytic poliomyelitis after the use of OPV among vaccine recipients or among their contacts

VAPP Vaccine recipients contacts of vaccine recipients 1 / 2.4 million 1 / 5.9 million doses doses (mainly among adults) with the first subsequent doses dose 1/ 750,000 1/ 5.1 million doses doses

Contraindications to OPV

1- Diseases associated with immune- suppression e.g Aids, malignancy. 2- Presence of immunodeficcent individuals in the household of vaccine recipients. 3- Diarrhoea is not a contraindication to OPV.

Advantages of Salk Vaccin:e Safe Stable Induce reliable humoral immunity not affected by other viruses Disadvantages of Salk Vaccine: Expensive Administration by injection High coverage is needed to protect populations

Recommended schedule

0 doseat birth 1st dose2 months 2nd dose4 months 3rd dose6 months 1st booster dose18 months 2ndbooster dose4 – 6 years

Polio Eradication Strategy

In 1988 WHO declared (stated) the goal of eliminating poliomyelitis in the World by the year 2000 The strategy for eradication consists of the following: Achievement of high routine immunization coverage with OPV Supplementary immunization in the form of National Immunization Days (NIDs)


Effective surveillance Mopping up campaign: Door-to-door immunization campaigns in areas where the virus persists