Chapter 27: Positivestrand RNA Viruses

1
Chapter 27 Positive-strand RNA Viruses

• Recall ()-strand RNA genome serves as mRNA in
  infected host cell
• Representative Viral Families
• Picornaviridae
• One of the largest families of viruses
  clinically relevant human animal viruses
• Togaviridae
• Flaviviridae
• Calciviridae

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Positive-strand RNA Viruses

• Common Features
• Replication in host cell cytoplasm
• Genomic RNAs serve as mRNAs infectious
• Genomic RNAs are non-segmented
• Virions do NOT contain any enzymes
• Virus-specific proteins synthesized as
  polyproteins processed by viral cellular
  proteases, yielding individual viral proteins
• Enveloped non-Enveloped

3
Picornaviridae

• 5 major genera
• Enteroviruses
• Rhinoviruses
• Cardioviruses
• Aphthoviruses
• Hepatoviruses
• Only MAJOR clinical diseases in humans with
  Enteroviruses, Rhinoviruses Hepatoviruses

4
Picornaviridae

• General Characteristics of Picornaviruses
• small, non-enveloped (naked), icosahedral
• Non-segmented, ss-RNA genome (mRNA)
• 4 structural proteins
• Survive well outside host (non-enveloped)
• Capsids very resistant to harsh environmental
  conditions (i.e., sewage systems) GIT
• Capsids stable in presence of heat detergents
  (EXCEPT Rhinoviruses) also stable in acids
• Genome is infectious
• VAPs bind to ICAM-1 receptors on epithelial
  cells, fibroblasts endothelial cells

5
Picornaviruses

• Overview of Virus Cycle
• Adsorption ICAM-1 bind VAPs
• Penetration endocytosis, viropexis (thru small
  channels)
• Uncoating capsid removal by passage thru
  channels in membrane genome released by acidic
  conditions in endosome
• Replication in CYTOPLASM
• Genome binds directly to ribosomes in cytoplasm,
  functioning as mRNA
• Viral proteins synthesized in 10-15 min
• Cleaved into viral products, e.g., RNA-dependent
  RNA polymerase (needed to make more RNA)
• ()RNA ? (-)RNA template ? ()RNA pool
• Maturation Assembly
• Release by cell lysis (non-enveloped virions)
  host cell dies

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Genus Enterovirus

• gt70 identified
• Includes Polioviruses (3 serotypes)
• Epidemiology
• Exclusively human pathogen human reservoir
• Mode of transmission p-p, indirect, fecal-oral
  fomite
• Ingestion of contaminated food or water
• Enteroviruses are stable _at_ low pH of stomach,
  replicate in GIT excreted in stool
• Initial replication in oropharynx and intestinal
  lympoid tissue then entry into blood (viremia)
  spread thru-out the body to target organs (i.e.,
  CNS for poliovirus)
• Stable _at_ pH 3 (acidic) in detergents, sewage,
  etc.
• Replicated _at_ temp gt33C

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Genus Enterovirus

• General characteristics
• Most are cytolytic cause damage to target/host
  cell
• Portals of entry URT, oropharynx, intestinal
  tract
• Sxs vary w/ tissue trophism
• Poliovirus w/ narrow trophism, recognizing a
  receptor expressed on anterior horn cells of
  spinal cord, drg, motor neurons, skeletal muscle
  cells, lymphoid tissue
• Cause viremia
• Cause damage to cell by preventing cellular mRNA
  from binding to ribosomes

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Genus Enterovirus

• Viral Replication
• Binding to specific receptors on host cell
  surfaces
• Parental RNA serves as a template for a
  (-)-strand RNA template from which multiple
  copies of progeny ()-strand RNAs are produced
• Translation
• Synthesis of single, long polyprotein, processed
  by viral proteases into structural proteins and
  non-structural proteins, incl. RNA polymerase

9
Genus Enterovirus

• Clinical Significance
• All enteroviruses can cause CNS disease
• Major cause of acute aseptic meningitis syndrome
  any meningitis (infectious or non-infectious)
  for which the cause is not clear
• Viral meningitis is distinct from bacterial
  meningitis
• Viral disease milder
• ? lymphocytes in CSF
• Glucose is NOT decreased
• Viral meningitis occurrence in Summer Fall,
  affecting both children adults
• Tx aimed _at_ sx reduction course of illness is
  benign no antiviral drugs available
• Dx viral isolation from stool samples (CNS in
  fatal cases)
• Evidence of infection rise in antibody titer
  against specific enterovirus

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Genus Enterovirus

• Clinical significance of Poliovirus infection
• Condition Poliomyelitis an acute illness
  destroying LMNs of spinal cord brainstem
  result flaccid, asymmetric weakness or
  paralysis
• Poliovirus is neurotrophic w/ narrow tissue
  trophism
• Sxs range from asymptomatic (in oropharynx and
  gut) to mild febrile illness (fever, HA, sore
  throat, malaise) to aseptic meningitis (HA,
  neck/back pain) to flaccid paralysis (d/t
  destruction of anterior horn cells of spinal cord
  motor cortex cell of cerebrum) to death d/t
  respiratory paralysis (destruction of medullary
  center cranial nerves)

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Genus Enterovirus

• Clinical significance of Poliovirus infection
• Initial Replication in lymphoid tissue of tonsils
  pharynx
• Virus is swallowed and then replicates in
  lymphoid cells of Peyers patches
• 1 viremia takes virus to CNS ventral (anterior)
  horn cells of spinal cord and motor cortex of
  cerebrum
• Produces paralysis of extremities
• 2 routes
• Virus may cross BBB into CNS
• Virus may infect skeletal muscle and move from
  muscles via motor nerves to CNS (retrograde
  transport) and infect the brain
• Bulbar paralysis of respiration, pharynx, vocal
  cords, etc. - results if virus spreads to other
  areas of CNS, like Medulla and CNs
• Paralytic Poliomyelitis
• Asymmetrical flaccid paralysis w/ no sensory loss
• Bulbar Poliomyelitis
• More severe may involve muscles of pharynx,
  vocal cords, and respiration death in 75 of
  patients

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Genus Enterovirus

• Clinical significance of Poliovirus infection
• 4 possible outcomes in non-vaccinated people
• Asymtomatic infection m/c 90-95 of cases
  infection is limited to oropharynx and gut no
  disease and no sequelae
• Abortive Poliomyelitis minor illness fever, HA,
  malaise, sore throat, nausea and vomiting within
  3 days of exposure 5 of cases
• Nonparalytic Poliomyelitis aseptic meningitis
  1-2 of pts virus progresses to CNS and
  meninges, causing back pain and muscle spasm
  sxs of minor illness
• Paralytic Poliomyelitis Major Illness 0.1-2.0
  of pts appears 3-4 days after minor illness has
  subsided virus spreads form blood to anterior
  horn cells of spinal cord and motor cortex of
  brain

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Genus Enterovirus

• Clinical significance of Poliovirus infection
• Prognosis
• 2/3 pts display permanent weakness w/ paralytic
  poliomyelitis
• Complete recovery rare w/ severe acute
  paralysis mechanical ventilation is needed b/c
  of respiratory muscle paralysis
• Complications
• Postpoliomyelitis Syndrome
• A variety of musculoskeletal sxs muscular
  atrophy/wasting and paralysis that create new
  difficulties w/ ADLs 25-30 years after the
  original attack of acute paralytic poliomyelitis
• Consequence of physiologic and aging ?s in
  paralytic pts already burdened by loss of
  neuromuscular functions (NOT a persistent
  infection, though)

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Genus Enterovirus

• Clinical significance of Poliovirus infection
• Treatment Prevention
• Management of infection is supportive and
  symptomatic
• Prevention Vaccination produces protective Ab
  response
• Salk Vaccine
• Inactive Poliovacccine (IPV) 3 strains of
  inactive (killed) poliovirus
• Sabin Vaccine
• Live, attenuated oral Poliovaccine (OPV) 3
  strains of live-attenuated poliovirus
• Trivalent oral polio vaccine
• Has potential for reversion to wild type, causing
  polio
• Both killed-virus inactive virus induce Abs
  and protect CNS from subsequent invasion from
  wild virus
• Since 1960s, Polio cases ?, but cases of
  vaccine-induced polio have been reported

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Genus Enterovirus

• Clinical significance of poliovirus infection
• Epidemiology
• WHO worldwide eradication program Americas
  were certified polio-free in 1994 still cases in
  Africa and Indian subcontinent
• Disease can occur in all age groups children
  more susceptible
• Developing countries, where conditions favor wide
  dissemination of virus, poliomyelitis disease
  of infancy early childhood (Infantile
  Paralysis)
• Person-to-person, indirect, fecal-oral route of
  transmission

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Genus Rhinovirus

• Sensitive unstable _at_ pH 3 (acidic)
• Replicates best _at_ temp 33C, thus confining
  them to URT, specifically nasal passages
• Consists of 100 different serotypes
• MAJOR CAUSE of the COMMON COLD or ACUTE RHINITS

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Genus Rhinovirus

• Epidemiology
• Accounts for gt ½ of all URT infections defined
• Mode of Transmission p-p, direct, respiratory
  droplets (aerosol) and indirect, fomites
• Hands are a major vector in the transmission
• Survives well outside the host
• Prevention wash hands well and often do NOT rub
  your eyes _at_ least ½ of cases get virus from
  fomites

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Genus Rhinovirus

• Pathogenesis
• Bind to ICAM-1 receptors on Respiratory
  Epithelial cells
• Temp pH restrict virus to URT
• Produce slow cytolytic effect
• NO viremia
• Most replication occurs in nose
• Infected cells secrete Bradykinin Histamine,
  which causes runny nose
• Interferon (generated in response to infection)
  may limit progression and contribute to sxs
• Infections are self-limited

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Genus Rhinovirus

• Clinical Significance
• Acute Rhinitis Common Cold
• Nasal obstruction accompanied by sneezing,
  rhinorrhea (runny nose), sore throat/mild
  pharyngitis, HA, malaise
• Seldom accompanied by a fever (NO FEVER), unless
  there is a 2 bacterial infection
• Sxs peak in 3-7 days may last up to 3 weeks
• Virally-infected cells secrete interferon, which
  limits progression of infection, but also
  contributes to sxs
• Nasal secretory IgA and serum IgM contribute to
  recovery, but produce minimal long-term
  protection d/t serotype conversion
• IS response is SLOW once enough virus is shed
  into Lymphatics (lymph nodes) get Immune
  Response
• Cell-mediated immunity plays very LITTLE role in
  controlling the virus
• Every time one sneezes gt 500-1000 infectious
  virions/mL of nasal secretion released!!!

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Genus Hepatovirus

• Refer to Hepatitis Slides

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Togaviridae

• General Characteristics
• Enveloped, icosahedral viruses
• ()-sense, ssRNA genome
• RNA serves as mRNA
• Encodes early (non-structural) late
  (structural) proteins
• 3 structural proteins
• Capsid (C) protein encloses viral RNA
  nucleocapsid
• Proteins E1 E2 glycoproteins form
  hemagglutinin-containing viral spikes that
  project from lipid bilayer
• Replication in Cytoplasm
• Buds thru host cell membrane
• 2 genera pathogenic in humans
• Alphavirus - neurotropic
• Rubivirus

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Genus Alphavirus

• Arthropod-borne viruses (ARBO)
• Transmission to humans domestic animals by
  mosquitoes
• Epidemiology
• Replication in wide variety of animals
• 2 Accidental Hosts
• Horses (equines) most susceptible
• Humans
• Pathogenesis
• Mosquito feeds on infected bird/rodent gets the
  virus in its blood then transmission to horses
  or humans
• Innoculation of an Alphavirus by a mosquito
  virus is carried directly to the blood (1
  Viremia)
• Then replication in the reticuloendothelial
  system (spleen, liver, BM), resulting in 2
  Viremia
• If viral load in 2 Viremia is great, viruses
  cross BBB in CNS (b/c of envelope) cause
  Encephalitis

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Genus Alphavirus

• Viral Replication
• Virus is internalized by receptor-mediated
  endocytosis following viral attachment
• Replication scheme for ()-sense RNA
• Clinical Significance
• Acute encephalitis
• Eastern Equine Encephalitis (EEE) host birds
  vector mosquitoes
• Western Equine Encephalitis (WEE) host birds
  vector mosquitoes
• Acute arthropathy Chikungunya virus
• Venezuelan Equine Encephalitis virus
• A febrile illness w/ flu-like syndrome host
  rodents vector mosquitoes
• Laboratory ID
• Rise in Ab titer (between acute convalescent
  sera)
• Viral isolation form CNS in fatal encephalitis
  cases
• Prevention
• Control of mosquito vector population

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Genus Rubivirus

• 1 member of genus Rubella Virus
• Etiological agent for Rubella (German Measles or
  3-day Measles)
• mild respiratory disease in children
• Consists of
• Mild fever malaise
• Swollen glands (lymphadenopathy)
• Viremia
• 3-day rash whole body exanthem in children
• More severe in adults, causing bone joint pain
• Only a respiratory disease does not cause
  readily detected cytopathic effects

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Genus Rubivirus

• Rubella Virus
• Major cause of Teratogenesis (chromosomal
  damage) thus a significant congenital disease
• Occurrence in pregnant ?s Congenital Rubella
  Syndrome
• If ? NOT immune gets infected ? viremia ?
  placenta ? viral infection of fetus
• In absence of Ab during pregnancy, virus
  replicates in placenta, spreads to fetal
  circulation and infects most of the tissues in
  developing fetus
• Virus alters normal cellular growth, alters rates
  of mitosis, and alters chromosomal structures
  (teratogenesis)

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Genus Rubivirus

• Rubella Virus
• Congential Rubella Syndrome Manifestations
• Cataracts other occular defects
• Heart defects
• Deafness
• Intrauterine growth retardation
• Failure to thrive
• Malnutrition in 1st year
• Microcephaly mental retardation

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Genus Rubivirus

• Rubella Virus
• Susceptibility of Normal ?
• Recording of Immune status of ? before pregnancy
  is important
• If pregnant ? has a negative Rubella Ab titer and
  she gets Rubella gt major risk toward the fetus
• Note ? will recover from the infection, but it
  is the FETUS who acquires the disease
• Recall Rubella is one of the classic childhood
  exanthems
• Laboratory Dx
• Nasopharyngeal/Throat swabs soloate and culture
  the virus
• Viral Ag detection by Immunofluorescence
• Serology
• ELISA Test for detection of IgM Abs
• Detection of IgG evidence of immunity (there is
  only 1 serotype)

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Genus Rubivirus

• Rubella Virus
• Immunity
• Rubella Abs appear in pts serum as rash fades
  and Ab titer rises rapidly over next 1-3 weeks
• Initial Ab IgM does not persist beyond 6
  weeks after illness if found 2 weeks after rash,
  then evidence of recent Rubella infection
• IgG Rubella Abs usually persist for life
• Epidemiology
• Rubella is worldwide in distribution
• Infection can occur thru-out year, but peaks in
  Spring
• Mode of transmission p-p, direct, respiratory
  droplet
• Fetus _at_ risk for Congenital Rubella Syndrome
• Pregnant ? gets the virus from another child, who
  acquired it from school
• use of Rubella Vaccine in U.S. has eliminated
  epidemic Rubella

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Genus Rubivirus

• Rubella Virus
• Treament Prevention
• No specific tx is indicated b/c it is a mild,
  self-limiting illness
• Attenuated, live Rubella vaccines available
  since 1969 single Ag or combined w/ Measles and
  Mumps (R in MMR vaccine)
• 1 purpose of Rubella Vaccine is to prevent
  congenital Rubella infections by decreasing
  of susceptible people in population, esp.
  children ?? therefore, there are fewer seroneg.
  mothers and thus smaller chance that they will be
  exposed to virus from contact with children
• Vaccine virus multiplies in body and is shed in
  small amounts, but does not spread to contacts
• Vaccinated children pose no threat to mothers who
  are susceptible and pregnant
• Vaccination in US has decreased incidence of
  Rubella from 70,000 cases in 1969 to only a few
  100 today
• Live Rubella vaccine usu. administered as MMR _at_
  12-24 months of age promotes both Humoral
  Cellular immunity

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Flaviviridae

• General characteristics
• Enveloped viruses
• Genome ss-RNA w/ 3 structural proteins
• Capsid (C) protein viral RNA icosahedral
  nucleocapsid
• 2 enveloped-associated proteins
• 3 genera
• Flavivirus
• Hepatitis C virus
• Pestivirus swine fever virus and bovine viral
  diarrhea virus

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Flavivirus

• gt 60 viruses all are Arthropod-borne
• Yellow fever
• St. Louis encephalitis
• Japanese encephalitis
• Dengue fever viruses
• West Nile virus (encephalitis)
• () strand/sense, ss-RNA, Enveloped
• Transmission to humans via bite of infected
  mosquito or tick (vector)
• Viruses are maintained in nature by replicating
  alternately in an arthropod vector vertebrate
  host

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Flavivirus

• Replication
• After attachment to host cell surface, virus
  internalized by receptor-mediated endocytosis
• Replication scheme for () sense RNA
• Genomic RNA translated into single, long
  polyprotein processed by virus-coded cellular
  proteases, giving rise to 3 structural 7
  nonstructural proteins
• Nucleocapsids formed in cytoplasm
• Virion maturation envelopment of nucleocapsid _at_
  cytoplasmic Golgi membranes (NOT cell membrane)
• Release by exocytosis or cell lysis

33
Flavivirus

• Clinical Significance Syndromes
• Encephalitis
• St. Louis Encephalitis
• 1st diagnosed in St. Lious, MO
• m/c non-equine encephalitis in KC area
• Host wild birds
• Vector Culex pipiens
• Japanese Encephalitis
• Tickborne encephalitis viruses
• Hemorrhagic fever or Yellow Fever
• Yellow Fever virus
• Can cause hepatocyte death (hepatitis), jaundice
• Sxs fever, HA, chills, nausea, vomiting
• Host Humans wild monkey primates
• Vector Aedes aegypticus

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Flavivirus

• Clinical Significance Syndromes
• Fever, myalgia rash (Dengue Fever)
• Sxs sudden onset of fever, HA severe myalgia
  may lead to shock, hemorrhaging death
• Host humans (urban setting), monkeys (jungle
  setting)
• Vector Aedes aegypticus
• NOTE Aedes aegypticus biological vector for
  both Yellow Fever Dengue Fever virus grows in
  the gut of this mosquito
• West Nile Encephalitis
• New virus disease in US setting
• Had been endemic in Northern Africa
• 1st seen in New England states and has migrated
  westward 1999 1st outbreak in NYC
• 1 death in KC area Summer 2003
• Host Cows Vector mosquito Culex pipiens
• Sxs acute, usually self-limited illness
  presentation fever, malaise, lymphadenopathy
  rash
• Aseptic meningitis or meningoencephalitis
  possible, esp. elderly

35
Flavivirus

• Laboratory Identification
• Serology 4-fold increase in Ab titer between
  acute convalescent stages
• Ag detection w/ virus isolation
• Prevention
• Live, attenuated vaccine for Yellow Fever
  available
• Vaccination in China and Japan for Japanese
  Encephalitis
• Vaccination in central Europe for tick-borne
  encephalitis
• Vector control elimination of mosquito breeding
  sites in urban area

36
Caliciviridae

• General Characteristics
• Small, non-enveloped, spherical particles
• Genome () sense, ss-RNA, nonsegmented
• Single species of capsid protein
• Norwalk Virus prototype human calcivirus
• Human disease viral gastroenteritis
• Replication in GIT shed in stool

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Caliciviridae

• Human Disease
• Viral gastroenteritis
• Diarrhea, vomiting, variable fever, non-bloody
  stool
• Etiological agent Norwalk Virus
• Infects intestinal brush border giving rise to a
  non-absorptive diarrhea
• Viral Cycle
• ()-sense RNA scheme
• Diagnosis
• Virus or viral Ag gt detected in stool using
  ELISA
• Epidemiology
• Mode of transmission p-p, indirect, fecal-oral
• Sources contaminated food or water, shellfish
  infected food-handler
• 60 of all nonbacterial gastroenteritis involves
  Norwalk virus
• Outbreaks schools, resorts, hospitals, nursing
  homes, restaurants, cruise ships
• 3 of gastroenteritis from day-care facilities
• Prevention
• Interrupt fecal-oral transmission
• Chlorinate water, etc
• No vaccine

38
Coronaviridae

• General characteristics of Coronaviruses
• ()-sense RNA
• Encodes for RNA-dependent RNA polymerase
• Enveloped
• Glycoproteins E2 functions as both VAP and
  fusion protein
• 2nd m/prevalent cause of the common cold
• Disease
• Acute Rhinitis
• Common Cold - 2nd m/c cause of acute rhinitis
  15-20 of cases
• Replicates best in epithelial cells of URT
  33-35C

39
Coronaviridae

• Viral Cycle
• Typical ()-sense RNA scheme except that the
  virion buds into ER, acquiring its envelope is
  released from cell by exocytosis
• Recovery
• Ab synthesis brings about resolution to sxs, but
  immunity is short-lived b/c of little IgA in
  respiratory tissue
• Diagnosis
• 4-fold increase in IgG
• Epidemiology
• Mode of transmission p-p, direct, respiratory
  droplets (sneezing)
• Infections mainly in infants children
• Prevention
• Prevent respiratory droplet transmission
• No vaccine

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Chapter 29 Negative-strand RNA Viruses

• Common Features
• enveloped
• Virions contain RNA-dependent RNA transcriptase
  that synthesizes viral mRNAs using the genomic
  (-)-strand as a template
• Genomic (-)-strand viral RNAs are NOT infectious
• Following entry penetration of host cell, 1st
  step in the replicative process is synthesis of
  mRNAs or ()-strand RNA templates
• Some genomes segmented, some non-segmented
• Most replicate in cytoplasm, except for
  Orthomyxovirus (replicates in nucleus)

41
Rhabdoviridae

• General Characteristics
• Enveloped, (-)-sense ss-RNA
• Bullet-shaped, enveloped virion containing a
  helical nucleocapsid coiled symmetrically into
  cylindrical structure
• Envelope contains a glycoprotein spike, composed
  of G-protein VAP is antigenic
• Nucleocapsid contains
• 1 (-)-sense, ss-RNA
• RNA-dependent RNA polymerase will polymerize
  its own RNA
• Major human pathogoen Lyssavirus (Rabies Virus)
• Etiological agent of RABIES

42
Rhabdoviridae

• Epidemiology
• Reservoir domestic wild animals gtraccoons,
  skunks, squirrels, foxes, bats domestic dogs and
  cats (in 3rd world countries)
• Urban Rabies dog principal reservoir rabies
  control programs in US have reduced significance
  of this
• Sylvatic Rabies Forrest Rabies wild animal
  reservoirs (rabies that occur naturally) account
  for most rabies in US
• KC area 1 skunk have natural fear of humans,
  but lose that fear when rabid
• NE US Fox rabies
• Raccoon in Southern US 2 in Midwest
• Bats are naturally rabid bat bites have
  accounted for all cases of rabies in past 10
  years in US
• Source bite of infected animal
• Incidence and distribution of human rabies
  parallels distribution of animal rabies 1-5
  human cases/year in US in which people have died
• Human rabies cases d/t infected dog (bite) 1
  case/year b/c of vaccination programs and limited
  contact with wild animals
• In US, rabies is most prevalent in cats b/c they
  are NOT vaccinated

43
Rhabdoviridae

• Overview of Viral Cycle
• Adsorption G-protein attaches virus to host
  cell internalized by endocytosis
• Virus is primarily neurotrophic, but also
  replicates in muscle cells
• Penetration
• Virus enters host cell by endocytosis
• Viral envelope fuses w/ endosomal membrane upon
  acidification of the vessicle
• Nucleoprotein is released into cytoplasm
• Replication
• Transcription of viral RNA occurs thru action of
  viral RNA-dependent RNA polymerase gt 5 mRNAs are
  transcribed/produced, each translated into a
  different viral protein
• Polymerase also produces ()-sense RNA template,
  required for replication of new (-)-sense RNA
  strands
• (-) strand RNA ? () strand RNA template ? (-)
  strand RNA

44
Rhabdoviridae

• Overview of Viral Cycle
• Assembly
• 2 phases
• Assembly of nucleocapsids in cytoplasm
• Envelopment release _at_ cell membrane
• Release
• virus buds thru host cell membrane and acquires
  it envelope
• Host Cell death lysis occur w/ most
  Rhabdoviruses, w/ exception of Rabies Virus
  (produces little discernible cell damage)
• Significant inclusion bodies are seen instead
  Negri Bodies

45
Rhabdoviridae

• Pathogenesis
• Most cells infected w/ Rhadboviruses exhibit cell
  death, w/ exception of Lyssavirus (Rabies Virus)
• Virus has affinity for Nicotinic Ach receptors on
  Nerve Cells
• Virus may directly infect nerve endings by
  binding to N-Ach receptors
• Virus also multiplies in muscles cells _at_
  inoculation site
• Virus reaches CNS by retrograde axoplasmic
  transport to drg and the spinal cord virus then
  moves from spinal cord to brain, causing an
  encephalitis
• Brain areas affected include
• Hippocampus
• Brainstem
• Ganglionic cells of Pontine Nuclei
• Purkinje cells of Cerebellum

46
Rhabdoviridae

• Pathogenesis
• From Brain, virus can travel along autonomic
  nerves, leading to infection of skin, cornea,
  lungs, kidneys, adrenal medulla, and salivary
  glands
• Contamination of saliva potentially leads to
  further transmission of the disease i.e., from
  bite of infected animal

47
Rhabdoviridae

• Clinical Significance
• Clinical Disease Rabies
• Neurological disease manifested by
• Hydrophobia (fear of water) most characteristic
• Triggered by PAIN associated w/ pts attempt to
  swallow
• Generalized seizures
• Disorientation
• Hallucinations
• Accompanied by various degrees of paralysis

48
Rhabdoviridae

• Clinical Significance (RABIES)
• Sxs may lead to coma, respiratory parlysis and
  death
• Disease is 100 FATAL in humans and animals,
  unless txed by vaccination
• Long incubation period (60-365 days avg 80
  days)
• Prodromal period (2-10 days) - consists of
• Fever
• HA
• Paresthesia
• GI upset
• Fatigue
• Anorexia
• Disease itself an Encephalitis, accompanied by
  neuronal degeneration
• Sxs d/t viral replication w/in cells of
  hippocampus, brainstem, cerebellum, and pons
• Virus disseminates from CNS via afferent neurons
  to skin of head neck, salivary gland, retina,
  cornea, nasal mucosa

49
Rhabdoviridae

• Summary
• Lyssavirus transmitted by animal bites 1st
  replicates in muscle
• Virus travels by retrograde axoplasmic transport
  after getting into nerves ? drg ? spinal cord
• Virus moves from spinal cord to brain
  (encephalitis
• Rabies infection usually results from bite of
  rabid animal
• Infection of animals causes secretion of virus in
  animals saliva and promotes aggressive behavior
  (mad dog)
• Transmission also via inhalation of aerosolized
  virus (as in bat caves)
• Rabies virus disseminates form CNS via afferent
  neurons to highly innervated sites, such as skin
  of head neck, salivary glands, retina, cornea,
  nasal mucosa, adrenal medulla, renal parenchyma,
  pancreatic acinar cells
• Little histopathologic ? seen in affected tissue
  other than the presence of Negri Bodies
• Rabies is 100 FATAL once clinical disease is
  apparent
• Long incubation period (avg. 80 days)
  therefore, 80 day window of time to STOP virus
  from reaching brain

50
Rhabdoviridae

• Diagnosis
• Dx is TOO LATE for clinical intervention
• Sxs neurological pattern gives presumptive Dx
  confirmed Dx if recent history of an bite
• Laboratory confirmation
• Cytopathology Hallmark of Rabies observation
  of intracytoplasmic inclusions in affected
  neurons
• Negri Bodies found in brain on infected animals
  and in 70-905of infected humans
• Dx
• Ag detection viral Ags in skin and CNS
• Serology Ab is NOT detectable until late in
  disease, when found in CSF and serum
• Most Dx and ID of Rabies gt done post mortem _at_
  autopsy to see the type of encephalitis that
  killed the patient.

51
Rhabdoviridae

• Control of Rabies
• Clinical Rabies is always FATAL unless treated
• Once sxs have appeared, supportive care can be
  given
• Induction of both Active Passive Immunity forms
  the basis of control Ab does prevent spread of
  virus to CNS

52
Rhabdoviridae

• Control of Rabies
• Rabies Post-Exposure Prophylaxis
• Only hope for preventing overt clinical illness
  in affected pt.
• Initiated for anyone exposed to a bite of by
  contamination of an open wound or mucous membrane
  to saliva or brain tissue of an animal suspected
  to be infected
• Tx of bite (wound) local tx of wound washed
  immediately w/ soap water, detergent
  inactivation of virus
• Passive Immunity Human Rabies Immunoglobulin
  (HRIG) provides Ab until pt produces Ab
  response to vaccine, ½ to source of bite
  neutralization) , rest into buttocks gt 5 doses
  administered over 1 month slows course of rabies
  disease allows active immunity to be generated
  in time to afford protection
• Active Immunization w/ Human Diploid Cell Vaccine
  (HDCV)
• Active immunization over interval of 30 days
• All shots in arm intramuscularly on days 1, 3,
  7, 14, 28
• Purpose to make pt start making own Abs in order
  to prevent rabies from reaching CNS

53
Paramyxoviridae

• Members of Paramyxovirus family divided into 2
  subfamilies
• Paramyxovirinae
• 3 genera
• Paramyxovirus parainfluenza viruses URT
  infections
• Rubulavirus Mumps Virus
• Morbillivirus Measles Virus
• Pneumovirinae includes Respiratory Syncytial
  Virus (RSV) major RT pathogen in children,
  causing Respiratory Syncytial Disease (RSD)

54
Paramyxoviridae

• General Characteristics
• Spherical (helical), enveloped nucleocapsid
• Non-segmented, (-)-strand RNA genome
• Glycoproteins found on envelope
• Fusion (F) protein promotes fusion of the virus
  w/ host cell membrane, facilitating virus entry
  into cytoplasm for replication
• All viruses w/in this group cause cell-to-cell
  fusion of infected cells, forming a syncytia and
  giant cells
• VAP
• Hemagglutinin-Neuraminidase (HN) ? Mumps virus
• Hemagglutinin (H) ? Measles virus
• G-protein ? RSV
• HN protein is involved in the binding of virus to
  the host cell Measles lacks the Neuraminidase
  activity

55
Paramyxoviridae

• General Characteristics
• Various enzymes/proteins carried in virion
• L protein RNA-dependent RNA polymerase
• P protein facilitates RNA synthesis
• (-)strand RNA ? ()stand RNA Template (mRNA) ?
  (-)strand RNA
• Overview of Virus Cycle
• Adsorption VAPs (HN, H, G) bind virion to cell
  surface receptors
• Penetration F-protein promotes fusion of virion
  envelop w/ host cell membrane also expressed on
  virally-infected cells and causes them to fuse,
  forming a syncytia (mulinucleated giant cells)

56
Paramyxoviridae

• Overview of Viral Cycle
• Replication occurs in host cell cytoplasm ()
  sense RNA template severs as the mRNA for protein
  synthesis and as a template for replication of
  new (-) sense RNA
• Maturation new (-) sense genomes interact w/
  other viral proteins to form nucleocapsids
• Release budding from host cell membrane, thus
  acquiring envelope

57
Paramyxovirus

• Type 1 and Type 3 Human Parainfluenzs Viruses
  (hPIV)
• Cause croup, pneumonia bronchiolitis
• Mainly seen in infants and children
• NO Viremia
• Def. Croup an acute viral disease of children,
  marked by a resonant barking cough, suffocative
  and difficult breathing, and laryngeal spasm b/c
  of respiratory distress, child is hypoxic (blood
  gas may show increased CO2 content)

58
Rubulavirus

• Type 2 and Type 4 Human Parainfluenza Viruses
• Same as Types 1 and 3
• Type 4 hPIV has been associated with mild URT
  illness in both children and adults (a bad
  cold)
• NO Viremia
• Mumps Virus
• Etiological agent for clinical disease known as
  Mumps
• Febrile illness characterized by Parotitis (acute
  benign swelling of salivary glands)
• Sxs fever, salivary gland enlargement/inflammati
  on, stiff neck upper back
• Incubation period 7-14 days
• Glands become infected during incubation period
  when virus is crossing into respiratory
  epithelial cells spreads via Parotid duct
  (Stensens duct) of by Viremia (or both) to
  salivary glands, which have the greatest density
  of receptors for the virus.

59
Rubulavirus

• Mumps Virus
• Viremia will carry virus to tissues of the body
• Testes (Orchitis inflammation of testes), ovary
  (Oophoritis inflammation of ovaries), pancreas,
  thyroid
• Testicular involvement in ?s can lead to
  sterility
• Cx CNS gt aseptic meningitis (meningoencephaliti
  s) 50 of pts

60
Morbillivirus

• Etiological agent for Measles (AKA Rubeola)
• 1 of 5 classic childhood exathems
• Serious disease w/ sxs of high fever 3 Cs
  (Cough, Coryza, Conjunctivitis)
• Photophobia
• Incubation period 7-13 days
• w/in 2 days of prodromal fever gt Koplik spots
  appear on mucous membranes, especially buccal
  mucosae (inside cheeks)
• w/in 12-24 hrs after Koplik spots appear,
  exanthem appears
• Maculopapular rash starting below the ears
  spreading over entire body lesions often run
  together
• Koplik spots early indicator of Measles sign
  that Measles infection is eminent w/in another
  day or so no other exanthem has this!

61
Morbillivirus

• Pathogenesis
• Measles virus replicated in cells of conjunctiva,
  RT, UT, lymphatic tissue, blood vessels, CNS
• Virus spread form initial sites of infection in
  lymphocytes gets into blood (viremia)
• Virus can pass from cell to cell escape
  detection by Abs
• Rash is d/t IS attacking virus-infected
  endothelial cells lining small blood vessels

62
Morbillivirus

• Complications
• Pneumonia accounts for 60 of deaths from
  Measles
• Subacute Sclerosing Panencephalitis
• Virus becomes a slow virus in brain appears
  as an extremely severe neurological sequelae
• Slow neurological ?s that occur over time b/c
  virus is slowly being produced

63
Pneumonvirus

• Etiological agent of Respiratory Syncytial
  Disease (RSD)
• Def. Syncytia group of cells in which protoplasm
  of 1 cell is continuous w/ that of adjoining
  cells.
• Similar to parainfluenza
• Not all that common in children more of a
  concern in younger children lt3 yoa
• Respiratory tract infection, ranging from common
  cold to pneumonia infection is localized to
  respiratory tract induces syncytia
• Pathological effect of RSV is direct viral
  invasion of respiratory tract epithelium,
  followed by immunologically-mediated cell injury
  necrosis of bronchi bronchioles leads to
  formation of plugs of mucous, fibrin and
  necrotic material w/in smaller airways
• Pneumonia results from virus spread (incl.
  syncytia)

64
Pneumovirus

• Only 1 serotype
• NO Viremia
• Natural infection does not prevent re-infection
  maternal Ab does not protect infant from
  infection
• Sxs
• Rhinorrhea (thin, watery discharge from the
  nose) prominent in older children 7 adults
• Bronchiolitis most severe manifestation in
  infants
• Cell-mediated immunity causes necrosis of bronchi
  and bronchioles w/ formation of a mucous plug,
  which obstructs the narrow passageways in young
  infants, leading to suffocation
• Air is trapped ? ventilation
• Can be fatal in premature infants

65
REMINDER

• Measles Mumps
• w/ Viremia
• Parainfluenza RSD
• NO Viremia

66
Diagnosis

• Measles
• Sxs Koplik spots are definitive
• Laboratory rarely used
• Ag detection
• Ab detection 4-fold ? in IgG Ab titer
• Cytopathology mulitnucleated giant cells w/
  cytoplasmic inclusion bodies seen in respiratory
  cells
• Mumps
• Sxs
• Laboratory viral detection in saliva, urine
  tissue specimens from pharynx, Parotid
  (Stensens) Duct, CSF.
• Serology mumps specific IgM or 4-fold ? in mumps
  specific IgG
• Parainfluenza
• Croup in children is very diagnostic
• Serology detection of specific IgM Ab
• RSD
• RSV cannot be grown in cell culture
• Dx form nsal washings respiratory secretions
  using immunofluorescence
• 4-fold ?in IgG Ab titer confirmatory

67
Epidemiology

• Measles
• Only infects humans can be spread before after
  onset of sxs is one of the MOST contagious
  infections known
• Spread via p-p, direct, respiratory droplets
• Mumps
• Only infects humans
• Human reservoir both symptomatic asymptomatic
• Highly communicable
• Spread via p-p, direct, respiratory droplet some
  direct contact
• Virus is present in resp secretions for as long
  as 7 days before clinical illness occurs (w/ no
  sxs) thus, it is virtually impossible to
  control the spread of the virus
• Parainfluenza
• Human reservoir virus are ubiquitous very
  common
• Spread via p-p, direct, respiratory droplets
  some direct contact
• Re-infection is common b/c immunity is
  short-lived
• RSD
• Human reservoir m/c in young children p-p,
  direct respiratory droplet
• 65-98 of children in day-care settings infected
  by age 3 everyone by 4 yoa
• Predominance in Winter highly contagious
• m/c cause of fetal acute respiratory tract
  disease lt2 yoa

68
Immunity

• Measles
• T-cells contribute to sxs, but also basis for
  resolution recovery
• B-cells form basis of prevention protection
• Ab- immunity Life-time does not often
  re-occur
• Only 1 serotype of Morbillivirus
• Mumps
• T-cell response to get rid of infected cells
• B-cells form basis of prevention protection
• Ab-based immunity Life-time does not often
  re-occur
• Only 1 serotype of Mumps Virus
• Parainfluenza
• Protective immunity following infection is
  short-lived
• Only IgM Ab response, which had NO memory
  re-infections thru-out life are common
• RSD
• Protective immunity following infection is
  short-lived
• No natural passive immunity
• Natural infection does NOT prevent re-infection
• IgM Ab produced by mother does NOT cross
  placenta thus infant is susceptible to infection
  when born

69
Control

• MMR Vaccine
• Measles/Mumps/Rubella Vaccination
• Polyvalent vaccine b/c it contains gt 1 Ag there
  are 3 1 Ags
• Measles gt active, attenuated Measles virus (MMR)
• Mumps gt active, attenuated Mumps virus (MMR)
• Parainfluenza gt NO vaccine available
• IS support only Tx and protection
• RSD gt NO vaccine available
• Passive immunity sometimes used in premature
  infants tx w/ FDA approved antiviral agent
  RIBAVIRIN administered by inhalation of
  nebulization

70
Orthomyxoviridae

• General characteristics
• Pleomorphic (spherical or tubular)
• Enveloped , helical nucleocapsid
• Negative-sense RNA w/ segmented genome
• 8 distinct segments 6 code for single protein
• Orthomyxoviruses divided into 3 types
• Influenza A
• Influenza B NOTE only A B are of clinical
  importance
• Influenza C
• Envelop with 2 glycoproteins
• Hemagglutinin (H protein or HA) projects as
  spikes and promotes adsorption major VAP
• Mutation-derived ?s responsible for minor
  (drift) and major (shift) ?s in antigenicity
• Neuramidase (N protein or NA) projects as spikes
  and promotes adsorption release
• Both H N influenza proteins are integral
  membrane proteins
• M (matrix) proteins underlies viral lipid
  membrane (fig. 29.10)
• Line the virion compose the capsid

71
Orthomyxoviridae

• General characteristics
• Transcription replication of influenza viruses
  occurs in Nucleus
• RNA viruses that replicate in the Nucleus
  synthesis of viral mRNA replication of the
  genome within nucleus
• Assembly occurs in cytoplasm
• Release is by budding thru cytoplasmic membrane,
  acquiring its envelope
• Viruses are prone to genetic variation via
  mutation
• Antigenic drift Ags ? little bit each year
• Antigenic shift after several antigenic drifts,
  a new genetic Ag Abs no longer combat virus
• Orthomyxoviruses the most variable viruses!

72
Orthomyxoviridae

• Viral Cycle
• Adsorption
• Hemagglutinin VAP
• Binds virion to sialic acid component/residues of
  host cell glycoproteins or glycolipids (RT
  epithelial cells)
• Is antigenic
• MUTATIONS responsible for antigenic shift (Type
  A)
• Neuraminidase
• Facilitate adsorption by hydrolyzing the sialic
  acid in respiratory epithelial mucosal cells,
  exposing the sialic acid acid receptors to which
  Hemagglutinin binds
• Penetration
• Virion is taken into host cell by
  receptor-mediated endocytosis

73
Orthomyxoviridae

• Viral Cycle
• Replication
• Viral genomic RNA serves as template for
  synthesis of viral mRNAs
• Each of 8 genome segments directs synthesis of 1
  ()-strand mRNA
• Virion contains 3 variants of RNA-dependent RNA
  polymerase
• Influenza transcriptase uses host cell mRNA as a
  primer for viral mRNA synthesis this removes the
  methylated cap form cellular mRNA, thus
  preventing it form binding to ribosomes result
  cessation of cellular protein synthesis cell
  death
• ()-sense RNA templates for each segment are
  produced and (-)-sense RNA genome is replicated
• Genomic segments are then transported from
  nucleus to cytoplasm
• mRNA formed in the NUCLEUS is translated into a
  spectrum of viral proteins by ribosomes in the
  cytoplasm

74
Orthomyxoviridae

• Viral Cycle
• Replication
• Among proteins synthesized are Hemagglutinin and
  Neuraminidase
• Maturation/Assembly
• (-)-sense replicas are transported to the
  cytoplasm, where they associate with new
  polymerase and other viral protein molecules
• Segments are held together by Matrix Protein M2,
  which then binds to cell membrane via matrix
  protein M1
• Only a few virions actually mature just a small
  of virions w/ a complete genome produced
  others are defective, but antigenic
• Release
• Complete defective virions bud from host cell
  membrane
• Envelope w/ its glycoprotein is acquired
• Total cycle takes about 8 hours

75
Orthomyxoviridae

• Pathology Clinical Significance
• Influenza infection solely of RT NO viremia
• Destruction of URT epithelial cells d/t host IS
  response (cytotoxic T cells)
• Prodrome of malaise HA (lasting few hours)
  leads to abrupt onset of FEVER, severe myalgia,
  and usually non-productive cough extreme
  drowsiness
• Virally infected cells can bind to opportunistic
  bacteria, resulting in 2 bacterial pneumonia
  (influenza infection promotes bacterial adhesion
  to epithelial cells of URT) then sputum is
  usually produced and becomes purulent
• Streptococcus pneumoniae
• Haemophilus influenzae
• Staphylococcus aureus

76
Orthomyxoviridae

• Pathology Clinical Significance
• Incubation period of 1-4 days acute illness
  lasts 3-5 day but cough may last for gt1 week
• Influenza is more severe in young children
  elderly
• Complications bacterial pneumonia and Reyes
  syndrome
• CN Reyes syndrome an acute