PicornaVirus- Characteristics
PicornaVirus- Characteristics
* pico = small, rna =RNA Viruses
+ icosahedral 30 nm
o naked nucleocapsid = Nonenveloped
o plus strand(+) RNA m-RNA
+ single stranded and capped for infectivity and packaging
+ this genome is infectious(should it be introduced into a cell)
o vertices of capsid creates canyon-like depressions which contain the VAP’s, VAP -1, VAP -2, VAP -3
+ most VAP bind to intracellular adhesion molecule -1(ICAM-1) expressed on epithelial cells, fibroblasts, and endothelial cells
PicornaViruses - Pathogens
* Four genera in this Family cause most Human disease
o Enterovirus enteroviruses
# stable at pH 3(acidic conditions), in detergents, sewage, etc
# replicate at temperature> 33 C
o Rhinovirus rhinoviruses
# sensitive and unstable at pH 3 (acidic conditions)
# replicates best at temperatures =33 C
* thus, confining them to the upper respiratory tract
o Hepatovirus
o Aphthovirus
PicornaViruses – Virus Cycle
* Adsorption the susceptible cells
+ appropriate receptors determine host range
+ ICAM - 1 or similar cellular receptors bind VAP’s
* 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
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
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
PicornaVirus - Pathogenesis
* Enteroviruses
o most enteroviruses are cytolytic
o they cause direct damage to the cell by preventing cellular m-RNA from binding to the ribosomes
o also viral m-RNA competes with cellular m-RNA for ribosomal binding sites
o symptoms vary with the tissue trophism of the enterovirus
o most enteroviruses cause viremia
* Rhinoviruses
o bind to ICAM-1 receptors on respiratory epithelial cells
o produce a slow cytolytic effect; not via cellular m-RNA mechanism
o temperature and pH restrict viruses to the upper respiratory tract
o no viremia occurs in Rhinovirus infections
o most Rhinovirus replication occurs in the nose
o 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
Picornaviridae - Enteroviruses
* Polio Viruses
* Coxackie Viruses
* Echo Viruses
* Entero Viruses
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
Enterovirus – Clinical Disease
* Poliomyelitis polio
o 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)
o Paralytic polio is generally to result of lower motor neuron damage and leading to a flaccid paralysis of the lower extremity
o Bulbar polio – causes damage to the respiratory centers in the medulla
Poliomyelitis - Pathogenesis
* initial virus replication is in lymphoid tissues of tonsils and pharynx
o 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
o 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
PicornaViruses – Other Clinical Diseases
* Herpangia = fever, sore throat with painful swallowing, anorexia and vomiting
o vesicular ulcerated lesion on the soft palate and uvula
o etiological agent is Coxsackie virus A, an enterovirus
o virus is shed from the lesions, respiratory droplets and in the feces(fecal-oral)
* Hand-Foot-Mouth Disease vesicular exanthem
o 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”
o 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
o etiological agent is Coxsackie virus B
o occurs at all ages, but most like threatening in neonates
* 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
o Hepatovirus
PicornaVirus - Diagnosis
* Enteroviruses
o 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
o 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
PicornaViruses - Diagnosis
* Rhinoviruses
o mostly based upon symptoms
o 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
Picornavirus - Epidemiology
Enteroviruses
o enteroviruses are exclusively human pathogens = human reservoir
o modes of transmission
+ Polioviruses
# p-p, indirect, fecal-oral
+ coxsackie and echoviruses
# p-p, aerosol droplets, and fecal-oral
* Rhinoviruses
o account for more than one-half of all upper respiratory tract infections defined and the “common cold”
o transmitted by respiratory droplets (aerosol), contact, and fomites
# hands are a major vector; 40 - 90 % people with colds
o Non-enveloped viruses are stable and survive on hands and fomites for hours
Enterovirus - Polio Control
* control of polio has centered around stimulation artificial active immunity via vaccines
o to shift the ratio of susceptible/immunes.
* Two Polio Vaccines
o Salk Vaccine - three strains of inactive polio viruses(IPV)
o 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
o Changes in Polio immunization guidelines – 1998
+ Use only inactive (Salk) vaccine
+ To reduce reversion of attenuated strains
ParamyxoViruses - Characteisteristics
* single-stranded, negative sense RNA viruses
o 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/Mumps
* Hemagglutinin Morbillivirus
* G protein RSV
o various enzymes/proteins carried in virion
+ L protein is the RNA dependent RNA polymerase
+ P protein facilitates RNA synthesis
Paramyxovirinae – Human Pathogens
* Respirovirus = Parainfluenza
* Rubulavirus = Mumps
* Morbilliviruse = Measles
* Pneumovirus = Respiratory Syncytial Disease
ParamyxoVirus- Viral Cycle
* Adsorption
+ VAP’s(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)
ParamyxoViruses – Clinical Disease
* Measles also called Rubeola
o serious febrile disease with symptoms of high fever and cough, coryza, conjunctivitis(three C’s) 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
o 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
o classic childhood exanthem caused by Morbillivirus
o 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
ParamyxoViruses – Clinical Disease
* Mumps
o 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
o etiological agent is Rubulavirus
ParamyxoViruses - Diagnosis
* Measles
o symptoms - the clinical symptoms are so distinct that laboratory comfirmation is seldom necessary
o 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
o symptoms although often asymptomatic
o 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
o cytopathology multinucleated giant cells in monkey kidney cell cultures
+ also infected cells “hemadsorb” guinea pig erythroctyes
Paramyxoviruses – Disease Complications
Measles Complications
o pneumonia accounts for 60% of deaths from measles
o Subacutesclerosing panencephalitis virus becomes a “slow virus” in the brain and appears as an extremely severe neurological sequalae
* Mumps
o Aseptic meningitis
o Ochitis
o Pancreatitis
ParamyxoViruses - Epidemiology
* Measles
o 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)
o 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
o human reservoir both symptomatic and asymptomatic
o highly communicable before immunization 90% of U.S. population was exposed before age 15
o p-p, direct, respiratory droplet transmission; some direct contact
# incubations carriers are infectious 7 days before symptoms
ParamyxoViruses – Clinical Disease
* Parainfluenza
o mild cold-like infection of the upper respiratory tract with symptoms of fever, coryza, pharyngitis, and mild bronchitis = common cold
o 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
o two serotypes of Respirovirus Viruses ( types 1&3)
o viruses remain localized in the respiratory tract; there is no viremia
o Cell-mediated immunity is responsible for cellular damage as well as recovery
o Antibody, esp IgA is protective and prevents additional infection for a short time; but re-infections are common throughout life
ParamyxoViruses – Clinical Disease
* Respiratory Syncytial Disease
o 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
o caused by the Pneumovirus (also called RSV) single serotype
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
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
ParamyxoViruses - Immunity
Measles
o 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
o antibody based immunity is “ lifetime”; does not often reoccur in same person
+ only one serotype of Morbilli(measles) virus
* Mumps
o same as with measles
o only one serotype of Mumps virus
o antibody based immunity is “lifetime”; does not often reoccur
* Parainfluenza
o Protective immunity following infection is short lived
+ Only IgM antibody response which has not memory
o Therefore, reinfections throughout life are common
* Respiratory Syncytial Disease
o same as with Parainfluenza; no natural passive immunity
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
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
o transcription and replication of influenza viruses occurs in the nucleus
o assembly occurs in the cytoplasm; close association with membrane
o release is by budding through the cytoplasmic membrane
o viruses are prone to genetic variation via mutation(recombination)
# antigenic drift
# antigenic shift
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
o 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
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
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
o 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
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 Reye’s syndrome
# Reyes syndrome is an acute encephalitis that affects children who have acute febrile illness; and is promoted by salicylates
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
OrthomyxoViruses - Epidemiology
* Reservoir Human and Animal Strains
o Source In the U.S. infected human
# In Asia/Orient both infected humans and infected animals
o 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
o Mode of Transmission
+ person-to-person, direct, respiratory droplets acute phase
# incubation carriers
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
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
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