Embed Size (px)
Citation preview
Viruses associated withrespiratory tract infections
Medical VirologyLecture 03
Youjun Feng
Center for Infection & Immunity, Zhejiang University School of Medicine
Orthomyxoviridae 正粘病毒 • Influenza virus 流感病毒 • Avian influenza virus 禽流感病毒 H5N1/H9N2/H7N9
Paramyxoviridae 副粘病毒 • Measles virus 麻疹病毒 • Mumps virus 腮腺炎病毒 • Parainfluenza virus 副流感病毒 • Respiratory syncytial virus, RSV 呼吸道合胞病毒
Coronavirus 冠状病毒 & SARS Coronavirus SARS 冠状病毒
Others• Adenovirus 腺病毒• Rubella virus 风疹病毒• Rhinovirus 鼻病毒• Reovirus 呼肠病毒
envelope
Togavirus Orthomyxovirus
Influenza virus
ParamyxovirusMeasles virus
Mumps virus
Respiratory syncytial virus-ssRNA segmented,
Parainfluenza virus
-ssRNA, envelope
Rubella virus+ ssRNA, envelope Picornavirus
Rhinovirus
Small RNA VirusesNon-enveloped+ strand RNA
Coronavirus
+ ssRNA, envelope AdenovirusdsDNA, naked, fibers
Reovirus
Rotavirus
segmented, dsRNA, naked
Introduction
Orthomyxoviruses (influenza viruses)orthos, Greek for "straight"; myxa, Greek for "mucus"
influenza viruse A, B, C
influenza viruse A, B—human disease
enveloped, segmented negative-sense RNA genome
flu-epidemics (local dissemination) or pandemics (worldwide)
Flu pendemics recorded
Orthomyxoviruses (influenza viruses)
Properties
Structure and composition
50 nm
Structure of influenza virus
Virion
Spherical, pleomorphic80-120 nm in diameter
Structure of influenza virus
HA - hemagglutinin
NA - neuraminidase
helical nucleocapsid (RNA plusNP protein)
lipid bilayer membrane
polymerase complex
M1 protein
RNA
1.Core
RNA
Composition of influenza virus
-ssRNA, 8 segments (type C 7)
NP (nucleoprotein)
RNA dependent RNA polymerase
Composition of influenza virus
2. envelope
M protein
lipid envelope
spike hemagglutinin(HA)
neuraminidase(NA)
5
1
Functions of hemagglutinin & neuraminidase
• HA causes agglutination of redblood cells.
• Viruses bind to the mucousmembrane cells by HA1 interactingwith membrane receptor.
• Virus’ envelope fuse with cellmembrane by HA2 forming afusion pore.
• NA help the virus to permeatemucin and escape from “non-specific”inhibitor.
• NA can increase the number offree virus particles, hence morevirus spread from the original siteof infection.
• NA is important in the final stagesof release of the new virus particlefrom infected cells.
Classification
type A, B, C : NP, M1 protein
sub-types: HA or NA protein
16 types HA; 10 types NA
NP
HA
M1
NA
Influenza A virus subtypes in the human population
Nomenclature
TypeHost of origingeographical origin
strain numberantigenic description of HA and NA
(parentheses)
e.g. A/swine/Iowa/3/70(H1N1)A/Hong Kong/1/68(H3N2)
Orthomyxoviruses (influenza viruses)
Properties
Antigenic drift and antigenic shift
Antigenic drift and antigenic shift
Antigenic Drift
antigenic drift
• Minor changes in antigens due togene mutation in influenza virus.
• HA and NA accumulate mutations– RNA virus
• immune response no longerprotects fully
• sporadic outbreaks, limitedepidemics
Antigenic Drift results in the emergence of dominantstrains in the yearly H1N1, H3N2, and strain B
Antigenic Shift
antigenic shift
• Major changes in antigens due togene reassortment in influenza virus.
• “new” HA or NA proteins
• pre-existing antibodies do notprotect
• might result in pandemics
where do “new” HA and NA come from?
• 16 types HA• 10 types NA
– all circulate in birds
• pigs– avian and human
where do “new” HA and NA come from?
where do “new” HA and NA come from?
reassortment
Antigenic shift, or reassortment, can result in novel and highlypathogenic strains of human influenza
why do we not have influenza B pandemics?
• so far no shifts have been recorded• no animal reservoir known
Orthomyxoviruses (influenza viruses)
Properties
Culture & resistance
Culture
• Chick embryo inoculation• Cell culture: PMK, MDCK
• No obvious Cytopathic effect (CPE)• Viral detection depends on RBC
agglutination phenomenon
HA binds to sialic acid receptoron RBC of human, chicken,guinea pig
Resistance
•Relatively hardy in vitro : maybe stored at 0-4C for weeks
•Ether and protein denaturants destroy infectively
•more resistant to alkaline pH than at acid pH (infectivity
and hemagglutination)
Orthomyxoviruses (influenza viruses)
Influenza virus infections in humans
Pathogenesis and pathology
Pathogenesis and pathology
Before infection
• DECREASED CLEARANCE
• RISK BACTERIALINFECTION
(staphylococci, streptococci,haemophilus influenzae)
• VIREMIA RARE
Viral NA lowers the viscosity of themucous film in the respiratory tract
• By person-to-person spread through respiratory droplets.
Transmission of Influenza Virus
•
•
•
AEROSOL– 100,000 TO 1,000,000
VIRIONS PER DROPLET
1-4 days INCUBATION
SHEDDING
Orthomyxoviruses (influenza viruses)
Influenza virus infections in humans:
Clinical findings
Classic Flu-like Symptoms
•Fever
•Malaise (physical discomfort, mild sickness)
•Myalgia (muscular pain)
•Sore throat (inflammation of the fauces and pharynx)
•Nonproductive cough
Symptoms in children
a) Higher fever
b) GI symptoms-abdominal pain and vomiting
c) Otitis media ( 中耳炎）d) Croup
e) Myositis (muscle inflammation)
Reye’s syndrome
• An acute encephalopathy of children and adolescents
• High (10-40%) mortality rate
• A recognized complication of influenza B, A and herpesvirusvaricellazoster infections
• Aspirin is to be avoided in children because of the associationwith Reye’s syndrome
Orthomyxoviruses (influenza viruses)
Influenza virus infections in humans:
Recovery
RECOVERY
• INTERFERON - SIDE EFFECTS INCLUDE:– FEVER, MYALGIA（肌痛）, FATIGUE （疲劳） , MALAISE（不适）
• CELL-MEDIATED IMMUNE RESPONSE
• TISSUE REPAIR– CAN TAKE SOME TIME
PROTECTION AGAINSTRE-INFECTION
• IgG and IgA– IgG less efficient but lasts longer
• antibodies to both HA and NA important– antibody to HA more important (can neutralize)
Orthomyxoviruses (influenza viruses)
Influenza virus infections in humans
laboratory diagnosis
DIAGNOSIS
• ISOLATION– NOSE, THROAT SWAB
– TISSUE CULTURE OR EGGS
• SEROLOGY– Hemagglutination
inhibition, HI/• RAPID TESTS
• provisional - clinicalpicture + outbreak
Orthomyxoviruses (influenza viruses)
Influenza virus infections in humans
Prevention and treatment by drugs
VACCINE
• inactivated• egg grown• sub-unit vaccine for children
• reassortant live vaccine approved 2003– for healthy persons (those not at risk forcomplications from influenza infection) ages 5-49years
VACCINE
• ‘BEST GUESS’ OF MAIN ANTIGENIC TYPES– CURRENTLY
•
•
•
•
type A - H1N1type A - H3N2type Beach year choose which variant of each subtype is thebest to use for optimal protection
Flu & Oseltamivirphosphate
Oseltamivirphosphate
Emerging viral diseases: Avian influenza virus
Orthomyxoviruses (influenza viruses)
Crossing of species barrier?
InfluenzaHong Kong, 1997: death of 7.000 chickenin 3 farms
Crossing of species barrier of a newinfluenza strain (H5N1) from poultry to man
20 humans became infected.
H5N1
One third die.No human to human transmission.
Killing of 1,6 millions poultry to preventspreading among poultry
Vietnam, Thailand, China, Laos, Korea,Japan, Kambodscha, Indonesien, 2004:reemergence of H5N1
Suspected human to human transmission
H7N9
Paramyxoviridae
••••
Measles virusMumps virusParainfluenza virusRespiratory syncytial virus, RSV
-ssRNA
measles (rubeola)Koplik's spots on mucosal membranes
Maculopapular rash (extendsfrom face to extremities)
Sub-acute Sclerosing Panecephalitis
(SSPE)
• Very rarely (7 in 1,000,000 cases)
• 1-10 years after initial infection
• progressive, fatal disease
• defective forms of the virus in the brain
• British "to mump" -to grimace or grin,
MUMPS VIRUS & Mumps
from the appearanceof the patient as aresult of parotidgland swelling.
parainfluenza virus & flu-likesymptom
RESPIRATORY SYNCYTIAL VIRUS
• Upper respiratoryinfection (‘bad cold’) inolder children and adults
• Lower respiratoryinfection- Bronchiolitisand/or pneumonia mayoccur after the upperrespiratory infection
• Severe infections occurin pre-term infants
CORONA VIRUSESCOLDS & SARS
The masked palm civet （果子狸）
Others
ADENOVIRUS• non-enveloped
• linear double-stranded (ds)DNA
• Icosahedral capsid,• capsomeres
hexons;at the vertices are 12 pentons,from which a fiber with aterminal knob projects. Thiscomplex is toxic to cells -causing rounding and death ofcells through inhibition ofprotein synthesis.
• Eye
Epidemic Keratoconjunctivitis (EKC), acute follicularconjunctivitis, pharyngoconjunctival fever• Respiratory systemCommon cold (rhinitis), pharyngitis (with or without fever),tonsillitis, bronchitis, pharyngoconjunctival fever, acuterespiratory disease (LRI)
• GenitourinaryAcute hemorrhagic cystitis
• GastrointestinalGastroenteritis.
RUBELLA (GERMAN MEASLES) VIRUS
• Togavirus• +ssRNA• Fetaldamage• live vaccine
(attenuatedstrain)
RUBELLA
Rash
Congenital rubella
皮疹
先天性风疹
Summary
1. Understand the structure of influenza virus2. Know the classification and nomenclature of influenza
viruses3. Master the function of hemagglutinin and neuraminidase ;
master the relationship between antigenic drift/shift with fluepidemic or pandemic.
4. Know the procedure for influenza virua replication.5. Understand the pathogenesis, pathology, clinical findings,
laboratory diagnosis, epidemiology, prevention and controlof influenza virus infection.
1.
2.
3.
Self control questionsThe principal reservoir for the antigenic shift variants of influenza virus appears to be:
(A) People in isolated communities such as the Arctic
(B) Animals, specifically pigs, horses, and fowl
(C) Soil, especially in the tropics
(D) Sewage
Each of the following statements regarding influenza virus is correct EXCEPT:
(A) Influenza A virus causes more epidemics and more serious disease than influenza B and C virusesdo
(B) Influenza viruses cannot be grown in cell cultures; hence, the diagnosis can only be madeserologically
(C) Influenza A virus undergoes major antigenic changes in its hemagglutinin (antigenic shift), whichallow the virus to evade existing immunity
(D) Influenza viruses are transmitted primarily by aerosol and primarily affects the lower respiratorytract
Each of the following statements concerning the antigenicity of influenza A virus is correct EXCEPT
(A) Antigenic shifts, which represent major changes in antigenicity, occur infrequently and are due tothe recombination (reassortment) of segments of the viral genome
(B) Antigenic shifts affect both the hemagglutinin and the neuraminidase
(C) The worldwide epidemics causes by influenza A virus are due to antigenic shifts
(D) The protein involved in antigenic drift is primarily the internal ribonucleoprotein
4.
5.
Self control questions
Each of the following statements concerning influenza is correct EXCEPT:
(A) Major epidemics of the disease are caused by influenza A viruses rather than influenza B and Cviruses
(B) Likely sources of new antigens for influenza A viruses are the viruses that cause influenza in animals
(C) Major antigenic changes (shifts) of viral surface proteins are seen primarily in influenza A virusesrather than in influenza B and C viruses
(D) The antigenic changes that occur with antigenic drift are due to reassortment of the multiple piecesof the influenza virus genome
Biochemical analysis of a virus reveals the genome to be composed of eight unequally sized pieces of single-stranded RNA, each of which is complementary to viral mRNA in infected cells. Which one of the followingstatements is UNLIKELY to be correct?
(A) Different proteins are encoded by each segment of the viral genome
(B) The virus particle contains a virus-encoded enzyme that can copy the genome into its complement
(C) Purified RNA extracted from the virus particle is infectious
(D) The virus can undergo high-frequency recombination via reassortment of its RNA segments
Self control questions
6. Please explain the molecular reasons related to sporadic outbreaks, limited epidemics or pandemic of “flu”.
7. Where do where do “new” hemagglutinin & neuraminidase of influenza virus come from?
8. Please explain sub-acute sclerosing panencephalitis (SSPE) as an example of persistent slow infection for
measles virus.
9. Term explanation: Antigenic drift and antigenic shift
Thank you so much!
