Polio Flashcards
Characteristics of polio
- Picornaviruses
- Icosahedral
- No envelope
- Acute infectious disease
- May affect CNS ( affects motor neurons leading to paralysis - usually permanent)
The polio virus
Typically an enteroviruses
Inactivated at heating at 55 degrees for 30 minutes but MgCl prevents inactivation
Restricted host range
Poliovirus requires a primate-specific membrane receptor, lack of this receptor makes the cell virus resistant
Three antigenic types (Types 1,2,3)
- Common antigens
- Unique neutralizing epitopes
Type 1 is the most frequent worldwide
Not affected by lipid solvents
A single nucleotide change can render virus attenuated
Pathogenesis of the poliovirus
The mouth is the portal of entry to the virus
Primary replication occurs in oropharynx or intestine ( The virus is present in the throat and stool before onset of illness)
From the oropharynx it moves into the lymph nodes leading to viremia
It them moves into the intestinal mucosa and further replicates in mucosa, peyers patches and mesenteric lymph nodes
Some viral particles travel along peripheral motor neurons an nerves
Some viral particles enter circulation again while other are shed in feces
In the CNS the virus affects the meninges of spina cord, anterior horn cells of brain stem and the brain leading to paralysis
Results of polio exposure
Exposure to the virus may lead to: -Inapparent infection without symptoms -Minor illness -Aspetic meningitis Paralytic poli ( Only 1% show clinical symptoms)
Inapparent infection of polio
No symptoms
Mild polio disease
Most common form of the disease -The patient has a monor illness charcterised by -Fever -Malaise -Drowsiness -Headache etc Recovery is in a few days
Nonparalytic polio (aseptic meningitis)
All the symptoms of mild polio disease but with stiff back and neck
Disease lasts 2-10 days and recovery is complete
Paralytic polio
Flaccid paralysis resulting from lower motor neuron damage
Incoordination secondary to brain stem infection and painful spasms of non-paralysed muscles may occur
Progressive polio muscle atrophy
Rare
Occurs decades after polio recovery
Epidemiology
Natural infections only in humans
Transmitted by feco-oral route
Excreted in feces for long periods : fecal contamination of food and water provides efficient mode of spread (Sewage is a reservoir)
Usually infects children
Diagnosis of polio
Presumptive diagnosis is clinical : acute flaccid paralysis
Confirmation is by :
-Isolation of virus from feces
Isolation
-Two stool specimen ("4 hrs apart) should be kept at 4-8 degrees during transit to lab
-CPE in 3-6 days
-Isolated with neutral antiserum
Prevention and control
Adequate sanitary practices
- Proper treatment of sewage
- Availability of drinking water
Vaccine
Inactivated polio virus(Salk)
-Is formalin inactivated
Dosage: Four inoculations over a period of 1-2 years
-e-IPV uses two doses
Oral polio vaccine(Sabin)
-Live attenuated
Taken at 0, 6, 10 and 14 weeks
Interference from other enteroviruses is possible with OPV
No antiviral drugs are available (Vaccine is the best option)
Outbreak response when AFP is detected
Children under 5 are given the oral vaccine within the district
The second round of dosing is done no earlier than four weeks after first
The team moves from house to house and cards are not checked (Vaccine given irrespective of the vaccination history)
Usually done in a high risk geographical area
Done during seasons of low polio transmission (cold season) to prevent excessive virus in environment
National Immunization days
Usually done in endemic areas
Interrupts the transmission of the wild type polio
Done twice a year, with doses 4 weeks apart
