PICORNAVIRUSES , polio virus

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PICORNAVIRUSES: 

PICORNAVIRUSES Dr.Praveenkumar Doddamani 06-08-2011

Why called PICO R N A VIRUSES ?: 

Why called PICO R N A VIRUSES ? small RNA (27 nm)

INTRODUCTION:: 

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:: 

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 & Composition: 

Structure & Composition Structure of a typical picornavirus . Exploded diagram showing internal location of the RNA genome surrounded by capsid composed of pentamers of proteins VP1, VP2, VP3, and VP4. Note the "canyon" depression surrounding the vertex of the pentamer .

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Structure of picornavirus RNA and genetic organization of its polyprotein

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Picarnoviridae family- 9 genera, (6 genera medically important ) ENTEROVIRUS RHINOVIRUS HEPATOVIRUS (Hepatitis A) PARAECHO VIRUS APHTHO VIRUS (foot &mouth disease) CARDIOVIRUS CLASSIFICATION

Picornavirus Replication: 

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

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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.

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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 surface N-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: 

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 GROUP: 

ENTEROVIRUS GROUP Poliviruses types 1 – 3 Coxsackieviruses group A ( 1 – 24 no type 23) Coxsackie viruses group B ( 1 – 6 ) ECHO viruses types 1 – 33 ( no 10 or 28) Entro viruses types 68 – 71

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Serotype Receptor Protein Enteroviruses Polioviruses 1-3 Poliovirus receptor (PVR) Coxsackieviruses A13, A18, A21 Intercellular adhesion molecule 1 (ICAM-1) Coxsackieviruses B1-B6 Coxsackie-adenovirus receptor (CAR) Coxsackieviruses B1, B3, B5 Decay accelerating factor (DAF) Echoviruses 1, 8 Very late antigen 2 (α 2 β 1 ) Echoviruses 6, 7, 11, 12, 13, 20, 21, 29, 33 DAF Enterovirus 70 DAF Parechoviruses Human parechovirus 1 (HPeV1) α V β 1 , α V β 3 integrins

POLIOVIRUSES: 

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:: 

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”

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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.

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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 .

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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)

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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.

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ANTIGENIC PROPERTIES :- 3antigenic types : 1,2,3 prototype strain are : Brunhilde & Mahoney :type 1 : Epidemics Lansing & MEFI : type 2 : endemic Leon & saukett : type 3 : epidemics. By ELISA & CFT – 2 antigens can recognised They are D [ dense] C [ coreless or capsid ]

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MODE OF INFECTION & PATHOGENESIS Source of infection is Infectied individual Apperant infection Inapparent infection Convalescent carriers

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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 )

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Seeded into CNS by blood Virus multiplies selectively in neurons Degeneration of Nissl’s bodies ( chromatolysis ) Aseptic meningitis In some cases progress to poliomyelitis

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CLINICAL FINDINGS :- Inapparent infection to a mild febrile illness to severe permanent paralysis. Incubation period : 7 – 14 days .

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STAGES: Abortive poliomyelitis Non paralytic poliomyelitis ( aseptic meningitis) Paralytic poliomyelitis Progressive post poliomyelitis muscle atrophy

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Abortive poliomyelitis :- Most common form Minor illness ( fever,malaise,headache,nausea,vomiting,constipation,sore throat) Recovers in few days Non paralytic poliomyelitis ( aseptic meningitis) Stiffness & pain in the black & neck . Lasts for 2 – 10 days, recovery rapid.

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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.

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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 .

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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

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Schema of the clinical and subclinical forms of poliomyelitis. This graphic representation shows the presence of virus and antibodies in relation to the development and persistence of the infection

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PREVENTION & CONTROL :- Nonspecific measures: Safe drinking water, improvement in sanitation, food hygiene. Vaccination: Both live and killed vaccines Killed vaccine- SALK parenteral vaccine Live attenuated vaccine- SABIN oral vaccine

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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.

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live attenuated vaccine :- sabin’s 1959 grown in primary or human diploid cell cultures . Stabilized by Mg Cl ₂ 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

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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 lakhs Type 3 virus : 3 lakhs Shelf life 4-8 ͦc 4months, -20 ͦc for 2yrs. Failure of cold chain

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Live oral attenuated polio vaccine :- Given orally 0 dose at birth 1 st dose 6 th wk. 2 nd dose 10 th wk. 3 rd dose 14 th wk. 4 th dose between 16 – 24 th month. 5 th dose 5 yrs of age.

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Property Sabin’s vaccine Salk’s vaccine Immunising agent Live, attenuated Killed virus Route of administration Oral Parenteral Immunity Mucosal ( IgA ) & Humoral ( IgG,IgM ,) Only humoral Reversion of virus to virulent Yes No

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Relative merits of killed and live vaccines :- Safety :- Attenuated strains:- Tend to acquire Neurovirulence OPV : Not safe in immunodeficient Efficiency :- Interference Diarrhoeal diseases Breast feeding Ease of administration : OPV is preferable .

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Economy :- Live vaccine i s very much economical. Nature of immunity :- Killed – systemic Oral – local and systemic Duration of immunity :- Killed – booster doses necessary Live – More lasting Use in epidemics :- OPV early during an epidemic Pulse polo campaign Global eradication

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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.

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EPIDEMIOLOGY :- 3 epidemiological phases : Endemic Epidemic Vaccine era Improved systems of hygiene and sanitation Promoted the transition from endemic to epidemic .

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Human are the only known reservoir Children are more susceptible transmitted through feco -oral route. 80% cases occur before age of 3 yrs.

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Factors infuencing incidence of paralysis Pregnancy carries increased risk of paralysis. Tonsillectomy during incubation period- bulbar paralysis. Injecting triple vaccine prepared using alum leads to paralysis of involved limb. Severe muscular exertion/trauma during pre paralytic stage increases risk of paralysis

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Treatment : Specific antiviral drugs for the treatment of poliomyelitis are not available, therefore management is supportive and directed to relief of symptoms

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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.

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PULSE POLIO immunisation

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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

THANK YOU…: 

THANK YOU… REFERANCES: Fields Virology Jawetz Medical microbiology,24 th ed Parks community medicine WHO website HOD sir notes. Internet images.