Lecture 3 Flashcards
What are the 6 respiratory viruses?
-Influenza
-Parainfluenza
-RSV
-Rhinovirus
-Covid
-Adenovirus
What are the properties of influenza viruses?
ssRNA(-) viruses
Pleomorphic envelope (varies in size & shape of envelope)
Helical nucleocapsid capsid
Segmented genome (8 RNA(-) segments)
Genetic structure enhances chance of reassortment of gene segments (Antigenic Shift)
Mutant strains cause epidemic, pandemic
Only influenza A & B important for human disease
Infects upper respiratory tract epithelium
Transcription & replication occurs in the nucleus
Assembly & release at plasma membrane
ssRNA(+)
Template for generating copies
ssRNA (-)
For packaging of new virus in nucleus
Influenza gene products (proteins)
associated with RNA genome
-PB2, PB1, PA – complex of 3 subunits forms the RNA polymerase
-NP – nucleocapsid protein
Other components produced in the host cell
HA – hemagglutinin – attachment protein, fusion protein
NA – neuraminidase – cleaves sialic acid in mucus, aids in viral spreading
M2 – membrane protein, channel, facilitates uncoating
M1 – matrix protein, structural
NS1 – IFN antagonist
NS2 – nuclear export protein
Influenza A host range
Humans, swine, avian, equines, marine mammals, bats
Influenza B host range
Humans, seals
Influenza C host range
Humans, swines
What are the properties of paramyxovirus
Pleomorphic envelope with specific viral attachment proteins
Helical nucleocapsid
Large, ssRNA(-) viruses
Linear genome
Carries nucleocapsid-associated proteins
3 important genera distinguished by attachment proteins
Cause major diseases including measles, mumps & RSV
Induce syncytia formation
Invade cells by membrane fusion, released by budding
Transmitted by aerosols & establish primary infection in respiratory tract
3 important genera of paramyxovirus
Morbillivirus
Measles virus (single serotype)
Paramyxovirus
Mumps virus (single serotype)
Parainfluenza virus 1-4
Pneumovirus
RSV (respiratory syncytial virus)
Metapneumovirus
Gene products of paramyxovirus
-Nucleocapsid-associated proteins
NP (nucleoprotein) – binds & protects viral RNA
P (polymerase phosphoprotein) – facilitates RNA replication
L (RNA polymerase)
-Viral-attachment proteins produced in host cell
F protein (membrane protein) – promotes fusion & viral entry
HN (hemagglutinin-neuraminidase)
Paramyxovirus (Parainfluenza virus & Mumps)
H (hemagglutinin) – binds surface receptors, no N
Morbillivirus (Measles)
G (glycoprotein) – for attachment, not a hemagglutinin
Pneumovirus (RSV)
M protein (matrix protein) – assembly of virions
Adenovirus Properties
No envelope
Icosadeltahedral capsid
dsDNA virus
linear genome
52 serotypes (1-7 most common)
Replicated & assembled in the nucleus
Lytic in permissive cells
Latent/persistent in non-permissive cells
Transformative only in non-human cells
Extensively studied (introns & RNA splicing)
Useful tools – gene replacement, anti-viral & cancer therapy
Adenovirus: Vaps & Receptors
-Fibers at vertices
viral attachment proteins
type-specific antigens provides specificity for serotypes
act as a hemagglutin
toxic to cells, along with pentose base
-Attach via Ig superfamily glycoprotein
Coxsackie adenovirus complex
-Also bind MHC I
Internalized by receptor-mediated endocytosis
Lyse vesicles & enter nucleus
Adenovirus gene products
E1A & E1B – inhibit p53 & p105RB
E2 – viral DNA polymerase
E3 – immunosuppressant (blocks apoptosis; decrease MHC I expression)
E4 – prevents apoptosis
Viral-associated RNAs (VA RNAs) – inhibit IFN response
L1 – L5 – structural/capsid proteins
Adenovirus Transmission & Disease
-Transmission
inhalation
close contact
oral/fecal
fomites
poorly chlorinated pools
Spread by viremia
Hallmark of infection – inclusion bodies without cellular enlargement
-Clinical Diseases (dependent upon tissue infected and virus type)
Acute febrile pharyngitis and pharyngoconjunctivital fever
Acute respiratory disease
Laryngitis, bronchiolitis, pneumonia
Conjunctivitis (pink eye, swimming pool conjunctivitis)
Gastroenteritis
PICORNAVIRUSES: GENERAL PROPERTIES
no envelope
icosahedral capsid
small, ssRNA (+) viruses
linear mRNA genome
replicated & assembled in the cytoplasm
large family of viruses
very resistant to harsh conditions
enteroviruses (tolerate wide pH range)
transmitted by fecal-oral route
Lytic viruses with specific tissue tropisms
PICORNAVIRUSES: DIFFERENT GROUPS
-Enteroviruses
Poliovirus
Coxsackie A virus
Coxsackie b virus
Echovirus
-Rhinovirus (common cold)
-Cardiovirus
-Aphthovirus
-Hepatovirus
Hepatitis A virus
RHINOVIRUSES: PROPERTIES
number one cause of common cold & upper respiratory tract infections
Use ICAM-1 as rhinoviral receptor
Prefer cooler temperatures
Less resistant than enteroviruses
cannot tolerate environment of GI tract
Acquired by inhalation as aerosols or by fomites
replicates primarily in the nose
CORONAVIRUSES: PROPERTIES
enveloped virion
long, flexible, helical genome
ssRNA(+) virus
envelope glycoproteins form club-like projections – “corona”
corona provides resistance to acids of GI tract
Infect upper respiratory tract epithelial cells
Released by exocytosis
Usually remains local due to optimal growth at temperatures less than physiological (33°C to 35°C)
Second most common cause of common cold
SARS – Severe Acute Respiratory Syndrome
MERS – Middle East Respiratory Syndrome
COVID-19 – world-wide pandemic
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