Orthomyxoviridae And Paramyxoviridae Flashcards
What are the viruses that are included in Paramyxoviridae?
- Parainfluenza virus
- RSV
- Metapneumovirus
- Mumps virus
- Measles (rubeola) virus
What is the virus that is included in orthomyxoviridae?
Influenza virus
What percentage of the entire world population gets infected with the influenza virus every year?
20%.
Describe briefly the structure of orthomyxoviridae.
- Spherical virions
- At the center lie 8 segments of negativ (-) stranded RNA put together with a protein (nucleocapsid protein - NP) into a helical symmetry.
- Surrounding the nucleocapsid lies an outer membrane studded with long glycoprotein spikes.
What are the two distinct types of glycoproteins?
- One with Hemagglutinin Activity (HA)
2. One with Neuraminidase Activity (NA)
What are the M proteins?
Anchoring the bases of these glycoprotein spikes on the inside of the viral lipid bilayer are membrane proteins. (M proteins)
What is the role of hemagglutinin?
- Can attach to sialic acid receptors - RBCs.
- Also on upper respiratory tract cell membranes.
- So hemagglutinin is essential for adsorption.
What will antibodies against hemagglutinin cause?
They will block the binding of the virus and prevent infection.
What is the action of neuraminidase?
Neuraminic acid is an important component of mucin, a substance overlying mucosal epithelial cells.
This enzyme cleaves neuraminic acid and disrupts the mucin barrier, exposing the sialic acid binding sites beneath.
How many types of influenza virus exist?
Three - A,B,C
What is the antigenic drift?
During viral replication mutations can occur in the HA or NA, leading to changes to the antigenic nature of these glycoproteins. The changes are small.
What occurs with antigenic shift?
Complete change of the HA and NA. This can only occur with influenza type A, because the mechanism involves the trading of RNA segments between animal and human strains.
What are the main complications of influenza?
- Pneumonia in the immunocompromised.
- Also lowers the host defenses against many bacteria - S.aureus, S.pneumoniae.
- New fever or failure to improve means DANGER.
What are the 4 broad categories of diagnostic tests for influenza?
- Virus isolation
- Detection of viral proteins
- Detection of viral nucleic acid (RNA)
- Serological diagnosis: 4-fold increase in specific antibody levels over 2 weeks.
The structure of paramyxoviridae is very similar to that of the orthomyxoviridae. What are the differences?
- The negative stranded RNA is in a single strand, not segmented.
- HA and NA are a part of the same glycoprotein spike, not 2 different spikes.
- They possess a fusion (F) protein that causes the infected host cells to fuse together into multinucleated giant cells.