Respiratory Viruses I: Infuenza Viruses Flashcards
The Major Viral Agents of ARD (8):
- Influenza
- Parainfluenza
- RSV
- Metapneumovirus
- Adneovirus
- Rhinovirus
- Coronavirus
- Bocavirus
Type A
- Humans
- Swine
- Birds
- Horses
- Seals
Type B
- Humans
- Seals
Type C
- Humans
- Swine
Structure of Influenza A
- 8 segments of single stranded (-) RNA
- Nucleoprotein covers (coats) RNA to form ribonucleoprotein complex
- M (matrix) surrounds ribonucleoprotein
- Envelope contains H (hemagglutinin) and N (neuraminidase) glycoprotein spikes
Influenza [] undergoes more significant antigenic changes than [] and [].
Influenza A undergoes more significant antigenic changes than B and C.
Genetic changes in Infuenza A occur due to:
- Antigenic drift and shift of both H or HA and N or NA glycoproteins due to mutation and recombination (reassortment), respectively
- Drastic changes in pandemics
Antigenic Drift
Antigenic Shift
How many types of H in Influenza A?
Three types of H (H1, H2 and H3)
How mant types of N in Influenza A?
Two types of N (N1 and N2)
Influenza Replication
i. Adsorption mediated by H by interacting with the receptor (sialic acid glycoprotein.
ii. N promotes smooth passage of the virus in the respiratory tract and later in viral release from infected cells.
iii. Uncoating in the cytoplasm to release viral genome.
iv. Only (-) RNA virus that replicates in the nucleus.
v. RNA segments migrate to nucleus to prime its transcription, uses host RNA primers, transcription/replication performed by viral RNA dependent RNA polymerase.
vi. Nucleocapsid assembled in the nucleus. vii. Buds through plasma membranes at sites where H and N spikes are expressed and M (matrix) protein has accumulated.
Where does Influenza replicate?
Only ( - ) RNA to replicate in the nucleus.
RNA segments migrate to nucleus to prime its transcription, uses [] RNA primers, transcription/replication performed by [] RNA dependent RNA polymerase.
RNA segments migrate to nucleus to prime its transcription, uses host RNA primers, transcription/replication performed by viral RNA dependent RNA polymerase.
Where is the Influenza nucleocaspid assembled?
Nucleocapsid assembled in the nucleus.
How is Influenza transmitted?
Transmission is direct, by infective droplet nuclei, or indirect, by hand transfer of contaminated secretions.
Where does Influenza replicate?
Ciliated epithelial cells in respiratory tract.
How does Influenza damage host?
- Functional and structural ciliary abnormalities due to viral replication in ciliated epithelial cells
- Shut off of host protein and nucleic acid synthesis
- Release of lysosomal enzymes and desquamation of ciliated and mucus-producing cells
- Chemotactic stimulus and pro-inflammatory cytokines cause major inflammation
- Damage renders host susceptible to invasive bacterial superinfection
Influenza Immunity
- Cell mediated & humoral immunity control infection
- Antibody to H is most protective
Influenza Incubation
1-2 days
Influenza Symptoms
- Abrupt onset leading to rapid development of symptoms including fever, myalgia, headache, muscle ache, chills, cough and fatigue.
- Improvement in 5-7 days, followed by prolonged cough, fatigue (2 to several weeks)
Progressive Infection can lead to:
- Progressive infection can cause viral pneumonia
- Damage caused by viral replication and acute inflammatory response render the host highly susceptible to invasive bacterial superinfection.
Most common secondary bacterial infection agents:
- Secondary bacterial infection causing pneumonia (Streptococcus pneumonia, Haemophilus influenzae, Staphylococcus aureus).
- Predisposing factors: age, heart, and lung defects
