PicornaVirus Characteristics

1
PicornaVirus- Characteristics

• pico small, rna RNA Viruses
• icosahedral 30 nm
• naked nucleocapsid Nonenveloped
• plus strand() RNA m-RNA
• single stranded and capped for infectivity and
  packaging
• this genome is infectious(should it be introduced
  into a cell)
• vertices of capsid creates canyon-like
  depressions which contain the VAPs, VAP -1, VAP
  -2, VAP -3
• most VAP bind to intracellular adhesion molecule
  -1(ICAM-1) expressed on epithelial cells,
  fibroblasts, and endothelial cells

2
PicornaViruses - Pathogens

• Four genera in this Family cause most Human
  disease
• Enterovirus enteroviruses
• stable at pH 3(acidic conditions), in detergents,
  sewage, etc
• replicate at temperaturegt 33 C
• Rhinovirus rhinoviruses
• sensitive and unstable at pH 3 (acidic
  conditions)
• replicates best at temperatures 33 C
• thus, confining them to the upper respiratory
  tract
• Hepatovirus
• Aphthovirus

3
PicornaViruses Virus Cycle

• Adsorption the susceptible cells
• appropriate receptors determine host range
• ICAM - 1 or similar cellular receptors bind VAPs
• Penetration
• internalized by endocytosis
• sometimes by viropexis thru small channels in the
  cytoplasmic membrane which removes the capsid
• Uncoating
• genome released by acidic conditions in the
  endosome
• capsid removed by passage thru channels in the
  membrane

4
PicornaVirus Replication

• Viruses replicate in the cytoplasm
• genome binds directly to ribosomes where in
  functions as m-RNA
• viral polyprotein is synthesized in 10 -15
  minutes
• polyprotein in cleaved into viral products
• cleavage proteases
• viral RNA dependent RNA polymerase
• misc proteins which inhibit cellular functions
• negative strand() template produced by viral RNA
  polymerase
• these templates then generate new plus stranded
  RNA

5
PicornaVirus Virus Cycle

• Maturation/Assembly
• structural proteins VP0, VP1, VP3 ect are cleaved
  from the polyprotein by the viral induced
  protease
• structural protein component assembly, then
  genome is inserted to complete maturation
• Release
• virions are released by cell lysis

6
PicornaVirus - Pathogenesis

• Enteroviruses
• most enteroviruses are cytolytic
• they cause direct damage to the cell by
  preventing cellular m-RNA from binding to the
  ribosomes
• also viral m-RNA competes with cellular m-RNA for
  ribosomal binding sites
• symptoms vary with the tissue trophism of the
  enterovirus
• most enteroviruses cause viremia
• Rhinoviruses
• bind to ICAM-1 receptors on respiratory
  epithelial cells
• produce a slow cytolytic effect not via cellular
  m-RNA mechanism
• temperature and pH restrict viruses to the upper
  respiratory tract
• no viremia occurs in Rhinovirus infections
• most Rhinovirus replication occurs in the nose
• infected cells secrete bradykinin and histamine
  which cause runny nose
• these cytokines also enhance the expression of
  ICAM-1receptors and may cause the virus to spread
  to adjacent cells

7
Picornaviridae - Enteroviruses

• Polio Viruses
• Coxackie Viruses
• Echo Viruses
• Entero Viruses

8
Rhinovirus Clinical Disease

• Acute Rhinitis Common Cold
• nasal obstruction accompanied by sneezing,
  rhinorrhea (runny nose), mild pharyngitis,
  headache, and malaise
• without secondary bacterial infection, rhinovirus
  infections seldom are accompanied by fever
• symptoms peak in 3-7 days, but may last up to 3
  weeks
• 500 - 1000 infectious virions per milliters of
  nasal secretion
• virally infected cells secrete interferon which
  limits the progression of infection , but also
  contributes somewhat to symptoms
• nasal secretory IgA, and serum IgG also
  contribute to recovery, but produce minimal long
  term protection due to serotype variation(type
  specific immunity)
• cell-mediated immunity plays very little role in
  controlling rhinoviruses

9
Enterovirus Clinical Disease

• Poliomyelitis polio
• symptoms range from asymptomatic (in the
  oropharynx and gut) to mild febrile
  illness(fever, headache, sore throat, malaise, to
  aseptic meningitis (headache, and pain in neck
  and back), to paralysis( destruction of anterior
  horn cells and motor cortex cells), to
  death(destruction of medullary center and cranial
  nerves)
• Paralytic polio is generally to result of lower
  motor neuron damage and leading to a flaccid
  paralysis of the lower extremity
• Bulbar polio causes damage to the respiratory
  centers in the medulla

10
Poliomyelitis - Pathogenesis

• initial virus replication is in lymphoid tissues
  of tonsils and pharynx
• virus is swallowed (resists acid and bile) and
  replicates in the lymphoid cells of the Peyers
  patches
• primary viremia takes the viruses to CNS,
  anterior horn cells and brain motor cortex -
  producing paralysis of the extremities
• virus may cross the blood brain barrier into CNS
• or virus may move via peripheral nerves to the
  CNS
• if virus spreads to other areas of the CNS, like
  medulla and cranial nerve, then bulbar paralysis
  of respiration, pharynx, vocal cords, etc
• if virus is shed back to the blood from the CNS,
  this is secondary viremia
• pathogenically polio viruses are neurotrphic
  (narrow trophism)
• humoral antibody is required for recovery and
  prevention

11
PicornaViruses Other Clinical Diseases

• Herpangia fever, sore throat with painful
  swallowing, anorexia and vomiting
• vesicular ulcerated lesion on the soft palate and
  uvula
• etiological agent is Coxsackie virus A, an
  enterovirus
• virus is shed from the lesions, respiratory
  droplets and in the feces(fecal-oral)
• Hand-Foot-Mouth Disease vesicular exanthem
• vesicular lesions on the hands, feet, mouth,
  tongue accompanied by mild fever
• Coxsackie virus A16
• etiological agent is virus is shed/transmitted
  from lesions and is also shed in the
  feces(fecal-oral)
• Pleurodynia acute onset of fever and unilateral
  lowthoracic, pleuritic chest pain which may be
  excruciating devils grip
• somtimes abdominal pain and vomiting muscles
  very tender on affected side
• etiological agent is Coxsackie virus B
• Myocarditis/Pericarditis acute febrile illness
  with sudden onset of heart faliure giving
  symptoms of myocardial infarction
• etiological agent is Coxsackie virus B
• occurs at all ages, but most like threatening in
  neonates

12
PicornaViruses Other Clinical Diseases

• Aseptic Meningitis acute febrile illness
  accompanied by headache, pain in neck and back
  including nuchal rigidity(signs of meningeal
  irritation)
• etiological agent is Coxsackie viruses A, B and
  Echoviruses
• may also lead to polio-like paralysis
• Respiratory Tract Diseae common cold (rhinitis)
• Coxsackie viruses A21/A24 Echoviruses 11/20
• Acute Hemorrhagic Conjunctivitis
• Enterovirus 70 and CoxsackieVirus A24
• Diabetes insulin-dependent
• Coxsackie B virus destruction of the Islets of
  Langerhans
• Hepatitis A Infectious Hepatitis
• Hepatovirus

13
PicornaVirus - Diagnosis

• Enteroviruses
• Laboratory
• Clinical Chemistry
• cerebrospinal fluid from CNS disease reveals
• lymphocytic pleocytosis (25 - 500 cell/ml)
• CSF glucose and protein
• glucose normal or slightly depressed
• protein normal or slightly elevated
• Serology
• detection of specific viral antibody in IgM
  fraction
• four fold increase in IgG from acute to
  convelescence
• Culture performed only for epidemiological
  confirmation
• polioviruses from pharynx or feces
• coxsackie or echoviruses from throat or feces
• monkey kidney tissue culture
• human embryo kidney tissue culture
• culture virus is specifically identified with
  antibody assays

14
PicornaViruses - Diagnosis

• Rhinoviruses
• mostly based upon symptoms
• laboratory identification of Rhinoviruses uses
• serology no antigen in common with all
  Rhinoviruses
• must find antibody to specific serotype
• culture human diploid fibroblasts at 33 C

15
Picornavirus - Epidemiology

• Enteroviruses
• enteroviruses are exclusively human pathogens
  human reservoir
• modes of transmission
• Polioviruses
• p-p, indirect, fecal-oral
• coxsackie and echoviruses
• p-p, aerosol droplets, and fecal-oral
• Rhinoviruses
• account for more than one-half of all upper
  respiratory tract infections defined and the
  common cold
• transmitted by respiratory droplets (aerosol),
  contact, and fomites
• hands are a major vector 40 - 90 people with
  colds
• Non-enveloped viruses are stable and survive on
  hands and fomites for hours

16
Enterovirus - Polio Control

• control of polio has centered around stimulation
  artificial active immunity via vaccines
• to shift the ratio of susceptible/immunes.
• Two Polio Vaccines
• Salk Vaccine - three strains of inactive polio
  viruses(IPV)
• Sabin Vaccine -three strain of active attenuated
  viruses(TVOPV)
• attenuated viruses are supposed to grow only in
  the oropharynx or intestinal tract, but not in
  nerve cells. In absence of reversion, this is the
  case and system responds immunologically
• Polio will be the next communicable disease to be
  eradicated
• Changes in Polio immunization guidelines 1998
• Use only inactive (Salk) vaccine
• To reduce reversion of attenuated strains

17
ParamyxoViruses - Characteisteristics

• single-stranded, negative sense RNA viruses
• helical(spherical) nucleocapsid surround by
  envelope (150 - 300nm)
• envelope glycoproteins
• F(fusion) protein - promotes fusion of virus with
  host cell
• all viruses in this group caused cell-cell
  fusion of infected cells forming synctytia and
  giant cells
• VAP - Hemagglutinin-Neuraminidase Paramyxovirus/Mu
  mps
• Hemagglutinin Morbillivirus
• G protein RSV
• various enzymes/proteins carried in virion
• L protein is the RNA dependent RNA polymerase
• P protein facilitates RNA synthesis

18
Paramyxovirinae Human Pathogens

• Respirovirus Parainfluenza
• Rubulavirus Mumps
• Morbilliviruse Measles
• Pneumovirus Respiratory Syncytial Disease

19
ParamyxoVirus- Viral Cycle

• Adsorption
• VAPs(HN, H, or G) bind virion envelope to cell
  surface receptors(sialic acid)
• Penetration
• F protein promotes fusion of the virion envelope
  with host cell membrane
• this same protein is expressed on virally
  infected cells and causes them the fuse forming
  syncytia(multinucleated giant cells)
• Replication occurs in the cytoplasm of host
  cells
• a positive sense() template is madefrom the
  negative-sense(-) RNA
• catalyzed by the virion based RNA dependent RNA
  polymerase
• the positive sense() RNA serves as the m-RNA for
  a protein synthesis and as the template for
  replication of the new negative-sense(-) RNA
• Maturation/Assembly
• new negative-sense genomes interact with the
  other viral proteins both structural and
  non-structural(L, NP, P,) to forms nucleocapsids
• virions then associate with host cell membrane
  via virus encoded matrix(M) protein
• Release
• Nucleocapsids bud from host cell membrane and
  acquire their envelope with its glycoproteins (
  F/HN)

20
ParamyxoViruses Clinical Disease

• Measles also called Rubeola
• serious febrile disease with symptoms of high
  fever and cough, coryza, conjunctivitis(three
  Cs) and photophobia
• incubation period 7 - 13 days
• within 2 days of prodromal fever lesion known as
  Kopliks appear on the mucous membranes
  especially the buccal mucosa. diagnosis
• within 12 - 24 hrs after Kopliks appear the
  exanthem appears
• maculopapular rash starting below the ears and
  spreading over the entire body - lesions often
  run together confluence
• patient is sickest and fever is highest the day
  rash appears
• classic childhood exanthem caused by
  Morbillivirus
• pathogenesis
• virus spreads from initial site of infection in
  lymphocytes and blood (viremia)
• in the tissues, the virus shows a major
  propensity to causedcell fusion resulting the
  giant cell formation
• virus can pass from cell to cell and escapes
  detection by antibody
• infection usually results in cell lysis
• rash is due to T-cells attacking the virus
  infected endothelial cells lining the small blood
  vessels

21
ParamyxoViruses Clinical Disease

• Mumps
• febrile illness characterized by parotitis( acute
  benign swelling of the salivary glands
• incubation period 7 - 14 days
• glands become infected during incubation period
  when virus multiplies in respiratory epithelial
  cells and spreads via Stenson duct or by viremia
  (or both) to the salivary glands
• the viremia carries the virus to tissues
  throughout the body( testes,ovary,pancreass,
  thyroid, etc.) and especially the the CNS
• CNS involvement occurs in approx 50 of patients
  and forms the basis for aseptic meningitis
• etiological agent is Rubulavirus

22
ParamyxoViruses - Diagnosis

• Measles
• symptoms - the clinical symptoms are so distinct
  that laboratory comfirmation is seldom necessary
• laboratory virus may be found in respiratory
  secretion, urine, blood, and sometimes in brain
  tissue
• antigen detection immunofluorence of pharyngeal
  cells
• antibody response IgM when rash appear four
  fold increase in IgG
• cytopathology multinucleated giant cells with
  cytoplasmic inclusion bodies seen in respiratory
  cells and urine sediment
• culture virus grows in human or monkey primary
  cell cultures
• Mumps
• symptoms although often asymptomatic
• laboratory virus found in salvia, urine, pharynx,
  Stensens duct, and cerebrospinal fluid
• serological detection of mumps specific IgM
• or fourfold increase in mumps specific IgG
• cytopathology multinucleated giant cells in
  monkey kidney cell cultures
• also infected cells hemadsorb guinea pig
  erythroctyes

23
Paramyxoviruses Disease Complications

• Measles Complications
• pneumonia accounts for 60 of deaths from measles
• Subacutesclerosing panencephalitis virus becomes
  a slow virus in the brain and appears as an
  extremely severe neurological sequalae
• Mumps
• Aseptic meningitis
• Ochitis
• Pancreatitis

24
ParamyxoViruses - Epidemiology

• Measles
• human reservoir virus is spread in respiratory
  secretion before symptoms(incubation carrier) and
  several days after symptoms appear(3 - 4 days
  after the apppearenc of the rash)
• measles is highly contagious via p - p, direct,
  respiratory droplets
• 85 of susceptibles in an exposed group
  (household) become infected by one single
  symptomatic individual
• Mumps
• human reservoir both symptomatic and
  asymptomatic
• highly communicable before immunization 90 of
  U.S. population was exposed before age 15
• p-p, direct, respiratory droplet transmission
  some direct contact
• incubations carriers are infectious 7 days before
  symptoms

25
ParamyxoViruses Clinical Disease

• Parainfluenza
• mild cold-like infection of the upper respiratory
  tract with symptoms of fever, coryza,
  pharyngitis, and mild bronchitis common cold
• may progress to a more severe bronchiolitis and
  pneumonia
• generally more serious in children in whom in
  progresses to laryngotracheobronchitis ( also
  known a Croup)
• Croup is due to subglottal swelling which closes
  the airway
• Croup ranks second only to RSV as the most severe
  lower respiratory tract infection in infants and
  children
• two serotypes of Respirovirus Viruses ( types
  13)
• viruses remain localized in the respiratory
  tract there is no viremia
• Cell-mediated immunity is responsible for
  cellular damage as well as recovery
• Antibody, esp IgA is protective and prevents
  additional infection for a short time but
  re-infections are common throughout life

26
ParamyxoViruses Clinical Disease

• Respiratory Syncytial Disease
• respiratory tract infections ranging from the
  common cold to pneumonia
• rhinorrhea is a prominent symptom in older
  children and adults
• bronchiolitis is a more severe manifestation in
  infants
• cell-mediated immunity causes necrosis of the
  bronchi and bronchioles with the formation of
  plug of mucus, fibrin. This obstructs the
  narrow airways in young infants leading to
  suffocation
• this traps air and decreases ventilation
• very fatal in premature infants
• caused by the Pneumovirus (also called RSV)
  single serotype

27
ParamyxoViruses - Diagnosis

• Parainfluenza Croup in children in very
  diagnostic otherwise symptoms cannot be
  distinguished from the common cold
• virus and virally infected cells are present in
  nasal washings and respiratory secretions and
  can be detected by cytopathology or
  immunofluorence antigen detection methods
• specific antibody (IgM) can be found using
  hemadsorption or hemmagglutination test
• Respiratory Syncytial Disease
• cannot be grown in cell culture
• most labaratory diagnosis is done on nasal
  washings and respiratory secretions using
  immunofluorescenc or enzyme immunoassay
• serological finding of fourfold increases in IgG
  provides confirmation

28
ParamyxoViruses - Epidemiology

• Parainfluenza
• human reservoir -viruses are ubiquitous and
  infection is very common
• p-p, direct, respiratory droplets transmission
  some direct contact
• reinfection throughout life is common since
  immunity is short lived
• some serotypes are seasonal
• parainfluenza 1, 2 (major agent of croup) in the
  autumn
• parainfluenza 3 occurs throughout the year
• Respiratory Syncytial Diseae
• human reservoir very common in young children
• 65 - 98 of children in day-care setting are
  infected by age 3
• infects everyone by age 4
• 25 - 33 of cases in children involve the lower
  respiratory tract
• RSV infections almost always occur in the winter
  and epidemic occur every year unlike influenza
  which sometimes skips a year
• highly contagious with an incubation period of 4
  -5 days
• most common cause of fatal acute respiratory
  tract disease in children under the age of 2

29
ParamyxoViruses - Immunity

• Measles
• T-cells contribute to symptoms, but also are
  thebasis of resolution and recovery antibody
  (B-cells) forms the basis of prevention and
  protection
• antibody does not contribute to complete recovery
  because the virus moves from cell to cell(direct
  extension
• antibody based immunity is lifetime does not
  often reoccur in same person
• only one serotype of Morbilli(measles) virus
• Mumps
• same as with measles
• only one serotype of Mumps virus
• antibody based immunity is lifetime does not
  often reoccur
• Parainfluenza
• Protective immunity following infection is short
  lived
• Only IgM antibody response which has not memory
• Therefore, reinfections throughout life are
  common
• Respiratory Syncytial Disease
• same as with Parainfluenza no natural passive
  immunity

30
ParamyxoViruses - Control

• Measles
• active attenuated measles virus one antigen in
  the polyvalent MMR
• inactive vaccine did not provide protection and
  complicated natural disease
• Mumps
• active attenuated mumps virus one antigen in the
  polyvalent MMR
• Parainfluenza
• no vaccine available
• immune system support is only treatment and
  protection
• RSV
• no vaccine available
• passive immunization is sometimes used in
  premature infants
• treated with Ribavirin

31
OrthomyxoViruses - Characteristics

• pleomorphic, enveloped, negative -sense RNA
  having a segmented genome
• 7 - 8 individual strands of RNA
• nucleoprotein(NP) and transcriptase associated
  with each strand
• envelope has two glycopreteins
• hemaggluttinin(HA) - projects as spikes and
  promotes adsorption
• genetic mutation (instability) producing
  antigenic variation
• neuraminidase(NA) - projects as spikes and
  promotes adsorption and release
• matrix proteins line the virion and compose the
  capsid
• transcription and replication of influenza
  viruses occurs in the nucleus
• assembly occurs in the cytoplasm close
  association with membrane
• release is by budding through the cytoplasmic
  membrane
• viruses are prone to genetic variation via
  mutation(recombination)
• antigenic drift
• antigenic shift

32
OrthomyxoViruses Viral Cycle

• Adsorption
• Hemagglutin (HA) is the viral attachment protein
• Binds the virion to the sialic acid component of
  epithelial cell receptors
• The viral component that causes hemagglutination
  of chicken and guinea pig red blood cells
• Is antigenic antibody against it is
  protective(neutralizing)
• mutations in the virus genome cause changes in
  the HA and are responsible for antigenic shift
  and drift in type A viruses
• Neuraminidase(NA) facilitates adsorption by
  hydrolyzing the sialic acid (neuramic acid) in
  respiratory mucous and thus exposing the sialic
  acid receptors to which the HA binds
• Penetration
• Virion is taken into host cell by endocytosis
• The virus is released from the endosome when the
  fusion-promoting portion of the HA fuses the
  viral envelope with the endosomal membane
• Acidification of the Matrix and NP also uncoat
  the virus during release from the endosome
  genome is this taken into cell nucleus

33
OrthomyxoViruses Viral Cycle

• Replication
• virions carry three variants of RNA dependent RNA
  polymerase
• during transcription of the viral RNA segments
  the polymerases used the cellular m-RNA in the
  nucleus as a primer this removes the methylated
  cap form the cellular m-RNA so that it cannot
  bind to the ribosomes resulting in cessation of
  cellular protein synthesis(translation)
• positive sense() templates are produced for each
  RNA segment
• these templates are then used to polymerize new
  negative sense RNA
• m-RNA formed in the nucleus is translated in to a
  spectrum of viral proteins by the ribosomes in
  the cytoplasm
• among the proteins synthesized are the HA and NA
  glycoproteins which are processes by the
  endoplasmic reticulum and the golgi and then
  incorporated into the host cell membrane

34
OrthomyxoViruses Viral Cycle

• Maturation/Assembly
• the negative sense replicas are transported to
  the cytoplasm where they associate with new
  polymerase and NP molecules
• these segment are held together by matrix
  protein(M2) which then bind it to the cell
  membrane via matrix protein(M1)
• since the mature virion must have 8 different RNA
  segments, only a few virions mature the others
  are defective but antigenic
• Release
• The complete and defective virions bud from the
  host cell membrane
• The envelope with its HA and NA glycoproteins is
  acquired during this process
• The cycle take about 8 hours

35
OrthomyxoViruses Clinical Disease

• Influenza
• a prodrome of malaise and headache(lasting a few
  hours) leads to abrupt onset of fever, servere
  myalgia, and usually a nonproductive cough
• the viruses infect the cells of the upper
  respiratory tract
• the infection first affects the mucous-secreting
  cells, and ciliated epithelial cells plus other
  cells the respiratory epithelium
• these changes in the upper respiratory barrier,
  allow the virus to move into the lower
  respiratory tract and infect the bronchial and
  alveolar epithelium
• virally infected cells binds opportunistic
  bacteria setting the stage for secondary
  bacterial pneumonia
• ultimately the mucosal surfaces throughout the
  respiratory tree become inflamed causing
  submucosal edema, hyaline membrane disease, and
  necrosis of alveolar walls
• incubation period of 1 - 4 days acute illness
  last approx 3 days but the cough may last more
  than a week
• influenza is more severe in young children and
  the elderly
• complications are bacterial pneumonia and Reyes
  syndrome
• Reyes syndrome is an acute encephalitis that
  affects children who have acute febrile illness
  and is promoted by salicylates

36
OrthomyxoViruses - Diagnosis

• symptoms especially when community epidemics
  occur laboratory distinguishes influenza from
  other respiratory viruses
• respiratory secretion
• cultured non-specific cytopathology
  hemadsorption hemagglutionation
• serology
• hemagglutinatin-inhibition
• Antigen detection
• Detection of Types A and B envelope glycoproteins

37
OrthomyxoViruses - Epidemiology

• Reservoir Human and Animal Strains
• Source In the U.S. infected human
• In Asia/Orient both infected humans and infected
  animals
• Antigenic Changes
• Antigenic Drift Influenza types A and B exhibit
  slights changes in the HA and NA antigens due to
  mutution perhaps some reassortment
• has only minor affect on the susceptibility of a
  population
• occurs every two to three years
• Antigenic Shift Only occurs in Influenza Type A
  viruses mostly due to reassortement of genes
  between human and animal strains
• results in complete changes in HA and NA
  antigens
• affects the susceptibility status of a population
  significantly
• occurs every 8 - 10 years Fig 56-5
• Mode of Transmission
• person-to-person, direct, respiratory
  droplets acute phase
• incubation carriers

38
OrthomyxoViruses - Epidemiology

• Pandemic resulting from Antigenic Shift
• 1918 HswH1 orignal swine flu
• 1947 A/FM/47/H1N1
• 1957 A/Singapore/57/H2N2
• 1968 A/HongKong/68/H3N2
• 1977 A/USSR/77/H1N1
• 1979 A/Bangkok/79/H3N2
• 1989 A/Beijing/89/H3N2
• 1991 A/Texas/91/H1N1

39
OrthomyxoViruses - Control

• Interrupt transmission this is almost possible to
  accomplish
• Immunization
• Inactivated(formalized) vaccine is produced each
  year and contains the three or four most recent
  antigenic strains which have affected the world
• intact virus
• splitt virus