Respiratory Viruses I (influenza, corona) Flashcards
Orthomyxoviruses
Influenza A, B and C
Paramyxoviruses
Measles
Mumps
Respiratory syncytial
Parainfluenza
Human influenza virus types and their infections
Influenza A - influenza pandemic
Influenza B - influenza
Influenza C - mild respiratory tract infections
Genome of human influenza virus
Segmented, single strand RNA
Capsid of influenza virus
Helical necleocapsid
Spikes on influenza virus
Two types of spikes
- hemagglutinin
- neuraminidase
Functions of hemagglutinin
- binds to the cell surface receptor (sialic acid) to initiate infection of the cell
- target of neutralising antibody
Function of neuraminidase
- cleaves neuraminic acid to release progeny virus from the infected cell
- also degrades the protective layer of mucus in the respiratory tract
Spike protein which functions at the beginning of the infection in influenza virus
Hemagglutinin
Spike protein which functions at the end of the infection in influenza virus
Neuraminidase
Types of antigenic changes
1) antigenic shift: major change reassortment/mixing of segments of the genome RNA
2) antigenic drift: minor change mutations in the genome RNA
Matrix proteins of influenza virus
M1- located b/w the internal nucleoprotein and the envelope
M2 - forms an ion channel b/w the interior of the virus and the external environment
Function of M1 protein
Structural integrity
Function of M2
Uncoats the virion after it enters the cell, frees the nucleocapsid containing the genome RNA, allowing it to migrate to the nucleus
Virion structure of orthomyxovirus
-Spherical virions
- centrally placed 8 segmented -ve stranded RNA put together with a nucleocapsid protein NP into a helical capsid
- outer membrane has glycoproteins spikes (hemagglutinin and neuraminidase)
- anchoring these spikes on the inside of the lipid bilayer are the membrane proteins (M-proteins)
Result of an antigenic drift
Results in milder disease in adults who have previously acquired antibodies
Result of an antigenic shift
Only occur with influenza type A
- involves trading of RNA segments between animal and human strains
- the virus wields a new HA or NA glycoprotein that has never been exposed to the human immune system so the entire human population would be susceptible, leading to devastating pandemics
Clinical findings of influenza virus
Fever, myalgia, headache, sore throat and cough
Resolves spontaneously in 4-7 days
Complications of influenza
S.aureus or S.pneumoniae
Reye’s syndrome (encephalopathy and liver degeneration, complication in children)
Lab diagnosis for influenza
- ELISA for viral antigen in respiratory secretions
- PCR
Treatment of influenza
Neuraminidase inhibitors (inhibits the release of virus from infected cells)
Structure of Corona virus
-centrally placed non-segmented, single stranded +ve RNA genome put together with a nucleocapsid protein into a helical capsid
- outer membrane has club shaped spikes in the form of a corona (halo)
Receptor of SARA coronavirus on the surface of cells
Angiotensin converting enzyme-2
Spike proteins of SARS coronavirus
S1- determines the virus-host range and cellular tropism via the receptor-binding domain
S2- mediates the membrane fusion of the virus to its potential cell host
