PICORNA VIRUS Picorna virus comes under the family
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PICORNA VIRUS
Picorna virus comes under the family Picorna viridae which consists of 4 genera. Medically important Picorna viruses are 1. Enterovirus 2. Parechovirus 3. Rhinovirus 4. Hepatovirus
Polioviruses
MORPHOLOGY: 1. Size: 27 – 30 nm. 2. Genome: RNA 3. Capsid: Icosahedral 4. Types : 1 , 2, 3
Pathogenesis: Children are more susceptible. The virus enters into the body by ingestion.
Virus Mouth Multiplies in lymphatic tissue, oropharynx and intestine Blood stream Spinalcord and brain Destroys the anterior horn cells of spinal cord
Clinical features: Earliest manifestation is fever malaise headache Drowsiness constipation sore throat.
There are 4 types of polio virus infections. 1. Inapparent infections ( 90 – 95 %) 2. Minor illness (4 – 8 %) 3. Non-paralytic poliomyelitis (1 -2%) 4. Paralytic poliomyelitis (0. 1 -2%)
Laboratory diagnosis: 1. Specimens: Viruses can be isolated from faeces, blood, pharyngeal washings, CSF and autopsy specimens (Spinal cord and brain). 2. Direct examination of the virus: Electron microscopy Immune electron microscopy.
3. Virus isolation Samples – Stool, Blood, Throat swab n Fecal excretion intermittent – sample collection on two separate days n Primary monkey kidney cell lines, Hela cells, HEp -2 Cells. n CPE in 2 -3 day n Neutralization with pooled specific antisera n Clinical and serological evidence
4. Serology n Neutralization test – Neutralizing antibodies appear early and persist for life n Complement fixation test – Used to identify exposure to poliovirus but not for type specific diagnosis.
Prophylaxis Active Early immunization by vaccines Crude suspensions of the spinal cord of infected monkeys Inactivated with formalin Ineffective / Vaccination poliomyelitis Tissue culture vaccines Salk : killed vaccine Koprowosky, Cox and Sabin : live attenuated vaccine
Salk’s killed polio vaccine Developed Three types of virus Monkey Pools kidney cells filtered Inactivated Assure Test in 1953 with formalin complete inactivation for safety and potency Issued for use
Cutter incident n 1955 n 100 cases of paralytic poliomyelitis in vaccinees and their contacts n Insufficiently inactivated vaccine
Administration of Salk’s vaccine n Injectable polio vaccine (IPV) n Subcutaneous or intramuscular route n Three primary doses , 4 -6 weeks apart n Booster dose : 6 months later, there after every 3 -5 years until the age of 18 years n First dose : 6 months of age n Combined with DPT
Advantages n Safe to administer – Persons with immunodeficiency diseases – Persons on corticosteroid and radiation therapy – During pregnancy
Disadvantages n Induces humoral antibodies but not local or intestinal immunity n Protects individual from paralytic polio but does not prevent reinfection with wild strain n Unsuitable during epidemics – More than one dose is required to induce immunity – Injection likely to precipitate paralysis
Sabin vaccine n Oral polio vaccine (OPV) n Live attenuated virus grown in primary monkey kidney or human diploid cell cultures n Monovalent / trivalent form n Mg. Cl 2 or sucrose stabilizes the vaccine against heat inactivation
Attenuated strain n Non neurovirulent n Able to set up intestinal infection n Should not acquire neurovirulence after serial enteric passage n Posses stable genetic characteristics (markers ) to differentiate from wild strains
Administration n Three doses , 4 -8 week intervals n Zero dose given at birth n Five doses in clinc -based programmes
Advantages Given orally, does not require use of highly trained personnel Induces Single both humoral and intestinal immunity dose can elicit substantial immunity Vaccinee excretes the virus, infects others who are immunised thereby Useful in controlling epidemics Relatively inexpensive
Disadvantages n unstabilised vaccines : -20 o. C deep freezer, transported on dry ice n Vaccine associated paralytic polio- 1 case per million vaccinees n Interference by other enteroviruses
Sl. n IPV OPV 1 Killed Live attenuated 2 Subcutaneous / IM oral 3 Circulating antibodies only Humoral and intestinal immunity 4 Does not prevent reinfection with wild strain, prevents paralysis Prevents paralysis and reinfection 5 Not useful in controlling Effectively used for epidemics controlling epidemics 6 Difficult to manufacture Easy to manufacture 7 Costlier cheaper 8 No stringent storage Stringent storage
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