Semester 2 - Enveloped RNA viruses Flashcards
What are some features of enveloped RNA viruses?
Generally less stable than non-enveloped viruses in the environment
Generally smaller than DNA viruses
Cause a wide variety of human infections
Require an RNA-dependent RNA polymerase (exception?)
What are some characteristics of orthomyxoviruses?
(-) ssRNA segmented genome
What are the different types of Influenzas and what are the differences between them?
Influenza A- most pathogenic, widest host range. Highly mutagenic, susceptible to antigenic drift and shift.
Influenza B - Relatively less pathogenic, narrow host range, relatively less mutagenic (1 serotype)
Influenza C - mild disease, narrow host range, relatively less mutagenic (1 serotype)
How are the Influenza A serotypes named?
Based on surface proteins hemagglutinin (H1-17) and neuraminidase (N1-9). Hemagglutinin binds sialic acid cellular receptor. Neuraminidase cleaves sialic acid upon egress
How does influenza A replicate?
- binding involves HA:SA
- endosome acidification (M2 proton pump)
- Gene expression and replication within the nuclear compartment (splicing, capping)
- Assembly (reassortment)
- Egress (NA)
Where does replication of influenza A occur?
In the nucleus. Gene splicing occurs in the nucleus (increases genetic diversity, conserves genetic space). 5’ mRNA cap is added in the nucleus (provides RNA stability, increases recognition by ribosomes)
How does having a segmented genome benefit the influenza virus?
Reassortment of segmented genomes introduces genetic variability
How does antigenic drift occur?
By random mutation. New serotypes occur when mutations to H or N sufficientyly escape antibody cross reactivity
How does antigenic shift occur?
By reassortment. Segments from multiple strains/serotypes are assembled into a single virion. Results in new combinations of serotypes (H1N1 + H5N3 = H5N1)
What is sialic acid?
A family of derivatives of neuraminic acid. Involved in cell surface expression.
What are the functions of sialic acid?
Cation transport across membranes
Recognition site within cellular receptors for endogenous molecules (hormones, cytokines)
Protection from erythrocyte degradation
Modification and regulation of function of a wide variety of molecules
What is 2,3-sialic acid?
sialic acid linked to galactose sugar by 2nd carbon residue of SA and 3rd carbon residue of Gal
What is 2,6-sialic acid?
sialic acid linked to 6th carbon residue of galactose
What animal is a reservoir for influenza in humans?
Pigs
What are the clinical features of an influenza infection?
chills, fever, sore throat, coughing, nasal congestion, muscle ache, fatigue, Pneumonia; primary (viral) or secondary (often bacterial)
How is influenza virus transmitted?
mucosal (respiratory droplets), seasonal pattern of infection. Possibly zoonotic?
What factors affect severity of infection?
age and immune status
strain/serotype
level of pre-existing immunity
How is influenza treated?
Seasonal vaccine 2 A strains H1N1 H3N2, 1 B strain
Antiviral drugs M2 proton pump inhibitors, neuraminidase inhibitors
Treat symptoms in milder cases
What are some characteristics of paramyzoviruses?
(-) ssRNA virus, enveloped
What are the human pathogens of paramyzoviruses?
respiratory syncytial viruses
parainfluenzavirus
Measles virus
Mumps virus
What is the Respiratory syncytial virus (RSV)?
Causes syncytia formation in infected cells
Lower respiratory tract infection
typically affects young children, seasonal pattern of infection (most common LRT infection in young children)
When are individuals most commonly infected with RSV?
Most individuals infected by 2-3 years of age
Prematurity a risk for severity
What are the two subtypes of RSV?
A and B, occurrence varies over the course of a season
What are the clinical features of an RSV infection?
Runny nose, sore throat, cough
Otitis media
Croup
Bronchiolitis, pneumonia, dyspnea, wheezing
How is RSV transmitted?
Direct contact
Transmission rates very high (survives hours/days on inanimate surfaces)
How is RSV treated?
Largely supportive
No vaccine
Prophylactic antibodies for high risk infants
Monitoring complications important for infants/toddlers
What is the second most common cause of respiratory tract infections in young children?
Parainfluenzavirus
How many serotypes of parainfluenzavirus are there?
4 hPIV 1-4
What are the clinical features of a parainfluenzavirus infection?
Lower respiratory tract
Croup
Bronchitis, pneumonia
Fever, malaise, fatigue
How is parainfluenzavirus treated?
Ribavarin (purine analog)
Severe cases require corticosteroid treatment to relieve RT inflammation
How many serotypes of the measles virus are there?
8 clades (A-H), 23 serotypes
What are the clinical features of a measles infection?
fever, cough, anorexia, rash
Early - white spots (koplik’s spots) in the mouth/throat
Later - generalized maculopapular, erythematous rash: itchy, ‘staining’
Subacute sclerosing panencephalitis (SSPE) rare
What is the treatment for measles?
vaccine-preventable (live attenuated)
Interferon and ribavarin (nucleotide analog)
How is measles transmitted?
contact, respiratory droplets
How many genotypes of the mumps virus is there?
Rubulavirus subfamily, several genotypes A-H
What are the clinical features of a mumps infection?
Feaver, headache, malaise, painful inflammation of the parotid gland. Also associated with inflammation of the testicles, prostate. Associated with sterility in post-pubescent adolescents.
CNS invasion rare - aseptic meningitis/encephalitis
How is mumps treated?
Vaccine preventable
Treatment is supportive
How is mumps transmitted?
mucosal (respiratory droplets)
What are some characteristics of the rubella virus?
+ ssRNA Rubivirus subfamily
aka the german measles
How is the rubella virus gene expressed?
+ RNA genome is used directly to translate viral non-structural proteins (genome serves as mRNA for NS proteins). Structural proteins are transcribed from the antigenome (-) into mRNA (+) before translation