INTRODUCTION: PICO - Small RNA viruses• Picornaviruses represent a very large virus family with respect to the number of members but one of the smallest in terms of virion size and genetic complexity• Two major groups of human• Enteroviruses• Rhinoviruses
GENERAL PROPERTIES:• Virion: Icosahedral, 28–30 nm in diameter, contains 60 subunits• Composition: RNA (30%), protein (70%)• Genome: Single-stranded RNA, linear, positive-sense, 7.2–8.4 kb in size, MW 2.5 million, infectious, contains genome-linked protein (VPg)• Proteins: Four major polypeptides cleaved from a large precursor polyprotein. Surface capsid proteins VP1 and VP3 are major antibody- binding sites. VP4 is an internal protein.• Envelope: None• Replication: Cytoplasm
Structure & CompositionStructure of a typical picornavirus. Exploded diagram showing internal location of theRNA genome surrounded by capsid composed of pentamers of proteinsVP1, VP2, VP3, and VP4. Note the "canyon" depression surrounding the vertex of thepentamer.
Structure of picornavirus RNA and genetic organization of its polyprotein
Picornavirus Replication• Occurs in the cytoplasm of cells.• First the virion attaches to a specific receptor in the plasma membrane.• Release of viral RNA in to the cell viral RNA translation.• RNA replication• Maturation by formation of protomers which are aggreagates Of VP0, VP1 and VP3
• these protomers assemble which package plus standed RNA to from ”provirions”• VP0 → VP4 &VP 2 → mature virus particles release by cell disintegration.• Multiplication cycle takes : 5 – 10 hours.
Entry of Poliovirus into Cells Nonenveloped poliovirus enters cells by forming a pore in the membrane of the cell. During interactions of poliovirus with its receptor major conformational rearrangements occur in the virus particle.The particles lose VP4 and the hydrophobic N-terminus of VP1 is displaced to the virion surfaceN-termini of VP1 forms a pore in the cell mebrane through which the RNA is released into the cytosol. Some evidence suggests that virus particles may undergo endocytosis in some cell types.
ENTEROVIRUSES• Relatively stable viruses surviving for long period in water, sewage,organic matter etc.• They resist pH of 3 for few Hrs.• Calcium chloride density is 1.34gm/ml.
ENTEROVIRUS GROUP1. Poliviruses types 1 – 32. Coxsackieviruses group A ( 1 – 24 no type 23)3. Coxsackie viruses group B ( 1 – 6 )4. ECHO viruses types 1 – 33 ( no 10 or 28)5. Entro viruses types 68 – 71
POLIOVIRUSES• Polioviruses are the cause of poliomyelitis, a systemic viral infection that predominantly affects the CNS, causing paralysis.polios =“gray”myelos =“marrow” or “spinal cord”• Now commonly shortened to polio, is descriptive of the pathologic lesions that involve neurons in the gray matter, especially in the anterior horns of the spinal cord.
HISTORY:• Sporadic poliomyelitis cases were published as early as 1840• the first descriptions of the natural history and neurologic complications of poliomyelitis were recorded in Sweden by Karl Oskar Medin in 1890.• In 1908, Landsteiner and Popper demonstrated that polio was caused by a “filterable virus”
• In 1949, Enders, Weller, and Robbins proved that poliovirus could be propagated in vitro in cultures of human embryonic tissues of non-neural origin.• This discovery facilitated experimental investigation of the pathogenesis of the disease in primates and the development of vaccines.• Bodian and associates first recognized the three distinct serotypes of poliovirus.• Salk reported in 1953 that human subjects could be successfully immunized with formalin-inactivated poliovirus, a discovery that rapidly led to an extensive field trial and licensure of IPV in 1955.
GENERAL PROPERTIES:• Poliovirus particles are typical enteroviruses. They are inactivated when heated at 55 °C for 30 min, but Mg2+,1 mol/L, prevents this inactivation.• purified poliovirus is inactivated by a chlorine concentration of 0.1 ppm, much higher concentrations of chlorine are required to disinfect sewage containing virus in fecal suspensions and in the presence of other organic matter.• Polioviruses are not affected by ether or sodium deoxycholate.
• Polio virus survives in sewage, water, fecal matter for days to weeks.• Survives in milk & ice creams for long period• Resists stomach acidity• Resists routinely used chlorination of water(0.1ppm)
Host range & cultivation:-• Restricted host range .(natural infection: MAN)• Monkeys – by inoculation into brain of spinal cord.• Chimpanzees – Oral → Asymptomatic → intestinal Carriers• Can be grown in Primary or continuous cell cultures derived from human or monkey kidneys.• Poliovirus requires a primate – specific membrane Receptor for infection ,• Liposomes & viral receptor gene introduction Converts resistant cells to susceptible cells.
ANTIGENIC PROPERTIES :-• 3antigenic types : 1,2,3• prototype strain are :1. Brunhilde & Mahoney :type 1 : Epidemics2. Lansing & MEFI : type 2 : endemic3. Leon & saukett : type 3 : epidemics.• By ELISA & CFT – 2 antigens can recognised• They are• D [ dense]• C [ coreless or capsid]
MODE OF INFECTION & PATHOGENESIS• Source of infection is Infectied individual Apperant infection Inapparent infection Convalescent carriers
Pathogenesis:- Ingestion of contaminated water Reaches & multiplies in intestinal epithelial cells Further multiplication in peyer’s patches Enters to regional lymphatics Enters into blood stream (viraemia)
Seeded into CNS by blood Virus multiplies selectively in neuronsDegeneration of Nissl’s bodies (chromatolysis) Aseptic meningitis In some cases progress to poliomyelitis
CLINICAL FINDINGS :-• Inapparent infection to a mild febrile illness to severe permanent paralysis.• Incubation period : 7 – 14 days.
• STAGES:• Abortive poliomyelitis• Non paralytic poliomyelitis ( aseptic meningitis)• Paralytic poliomyelitis• Progressive post poliomyelitis muscle atrophy
Abortive poliomyelitis :- Most common form Minor illness (fever,malaise,headache,nausea,vomiting,constipation,sore throat) Recovers in few daysNon paralytic poliomyelitis ( aseptic meningitis)Stiffness & pain in the black & neck .Lasts for 2 – 10 days, recovery rapid.
Paralytic poliomyelitis :-• Flaccid paralysis from lower motor neuron damage.• Incoordination due to brain stem invasion• maximal recovery Within 6 months with residual paralysis lasting longer.Progressive post poliomyelitis muscle atrophy:-• A recrudescence of paralysis & muscle wasting in patients decades after their experience with paralytic poliomyelitis.
LABORATORY DIAGNOSIS :-A. Recovery of virus :-• Throat swabs – soon after onset• Rectal swab or stool – Longer periods• CSF – virus not demonstrated/not recovered• Specimens kept frozen during transit• Human or monkey kindly cell cultures are inoculated, incubated & observed.• CPE appear in 3 – 6 days - Infected cells Round up & become refractile & pyknotic.• Isolated virus is identified and typed by neutralization with specific antiserum.
B. Serology :-• By CFT or• Neutralization , using Paired serum samples.IMMUNITY :• Type specific• Passive immunity is from mother to off spring during the first 6 months of life.• Ig M , Ig G – Blood• Ig A, - Immunity against intestinal infection
Schema of the clinical and subclinical forms of poliomyelitis. This graphic representationshows the presence of virus and antibodies in relation to the development andpersistence of the infection
PREVENTION & CONTROL :-Nonspecific measures:a. Safe drinking water,b. improvement in sanitation,c. food hygiene.Vaccination: Both live and killed vaccines1. Killed vaccine- SALK parenteral vaccine2. Live attenuated vaccine- SABIN oral vaccine
Killed :- salk 1953• Formalinized vaccine prepared from virus• Grown in monky kidney cultures.• 4 inoculations and boosters• induces humoral antibodies.• 3Doses, 4-6wks , booster 6 month.• Cutter incident.
live attenuated vaccine :- sabin’s 1959• grown in primary or human diploid cell cultures.• Stabilized by Mg Cl₂ and kept at 4 ͦC for weeks.• Live vaccine multiplies infects and Immunizes• progeny of vaccine Virus are disseminated in the community.• Multiple doses to establish permanent immunity• Up to 5 doses 4 weeks apart
• Ig M & Ig G antibodies and Ig A antibodies in the intestine.• OPv contains :-Type A virus : 10 lakhs TCID50 per Dose(0.5ml)Type 2 virus : 2 lakhsType 3 virus : 3 lakhs• Shelf life 4-8 ͦc 4months, -20 ͦc for 2yrs.• Failure of cold chain
Live oral attenuated polio vaccine:-Given orally 0 dose at birth 1st dose 6th wk. 2nd dose 10th wk. 3rd dose 14th wk. 4th dose between 16 – 24th month. 5th dose 5 yrs of age.
Property Sabin’s vaccine Salk’s vaccineImmunising agent Live, attenuated Killed virusRoute of Oral ParenteraladministrationImmunity Mucosal (IgA) & Only humoral Humoral (IgG,IgM,)Reversion of virus Yes Noto virulent
Relative merits of killed and live vaccines :-Safety :-Attenuated strains:- Tend to acquire Neurovirulence OPV : Not safe in immunodeficientEfficiency :- Interference Diarrhoeal diseases Breast feedingEase of administration :OPV is preferable .
Economy :- Live vaccine is very much economical.Nature of immunity :- Killed – systemic Oral – local and systemicDuration of immunity :- Killed – booster doses necessary Live – More lastingUse in epidemics :- OPV early during an epidemic Pulse polo campaign Global eradication
VACCINE-ASSOCIATED PARALYTIC POLIOMYELITIS• The only adverse reaction associated with OPV is the rare occurrence of VAPP, which affects approximately 1 person/2.6 million OPV doses distributed.• For immunocompetent patients, the clinical features and outcome of VAPP differ little from disease caused by naturally occurring polioviruses.• More than 80% of recipient and contact cases are associated with the first dose of OPV.• OPV virus types 3 and 2 are more common causes of VAPP than type 1.
EPIDEMIOLOGY :-• 3 epidemiological phases : Endemic Epidemic Vaccine era• Improved systems of hygiene and sanitation Promoted the transition from endemic to epidemic .
• Human are the only known reservoir• Children are more susceptible• transmitted through feco-oral route.• 80% cases occur before age of 3 yrs.
Factors infuencing incidence of paralysis1. Pregnancy carries increased risk of paralysis.2. Tonsillectomy during incubation period- bulbar paralysis.3. Injecting triple vaccine prepared using alum leads to paralysis of involved limb.4. Severe muscular exertion/trauma during pre paralytic stage increases risk of paralysis
Treatment :• Specific antiviral drugs for the treatment of poliomyelitis are not available,• therefore management is supportive and directed to relief of symptoms
Global Eradication of poliomyelitis:-• Eradication is possible.• WHO has started the programme on 1988.• Aimed to eradicate the disease by 2000.• Poor progress in many countries a set back.• PULSE immunization : vaccine to all children in a region on a same day.
INDIA :• 2006 – 60 cases were reported• 2011 till date only 1 case is reported West Bengal.Pulse polio immunization• OPV is given to children of 0-5 years age on single day, regardless to previous immunization• 2 rounds – 4-6 weeks apart• During low transmission season – nov - feb