Viral adaptations (7.1) Flashcards
How many classes of structures do viruses have? Describe how class 1 replicates
7; Class 1 must enter the host’s nucleus before it can replicate, and requires the host’s polymerase to replicate its own viral genome
Where do RNA viruses replicate? How do positive and negative strand RNAs infect?
Within the cytoplasm (they don’t have to use the host’s polymerase); so they’re less dependent on the host’s functions
A positive strand RNA directly accesses the host’s ribosomes and immediately forms proteins
Negative strand RNAs can’t immediately access the ribosomes but still replicate quickly
Describe the slightly differing methods of how influenza, polio and HIV may enter a host cell
Virus initially attaches to outside surface, creates an endosome.
Polio causes a pore like structure between itself and the cytoplasm and genetic info is injected through
In HIV; causes receptors specific sites and there is membrane fusion
How do enveloped and non enveloped viruses enter the host cell?
Enveloped viruses: require membrane fusion
Non enveloped viruses: genome usually delivered across a membrane by a pore
What are the three main functions of interferon alpha and beta?
Prevent viral replication by
- Activating host genes that destroy viral mRNA
- Inhibit translation of viral proteins
- Increase the expression of ligands for NKCs - activating NKCs to kill virus infected cells
What produces interferon and what does interferon interact with? What is the end affect?
Produced by infected cells and interacts with receptors on uninfected cells which causes a cascade of events intracellularly forcing the cell to enter an ‘antiviral state’; meaning the cell will inhibit viral protein synthesis, degrade viral RNA or inhibit the final assembly of the virus.
Where in the body does influenza primarily manifest? When is this virus more common and what is the most common method of its spreading? How is the prognosis?
Primary manifestation is severe respiratory problems, occurs more frequently in the winter and is most commonly spread through droplet transmission. Has a significantly high mortality rate
What type of virus is the influenza virus and what family is it in? What are the three major serotypes and what differentiates them?
It’s a single stranded RNA virus that allows a high rate of mutation, part of the orthomyxovirus family (surrounded by an envelope). The three serotypes are A, B and C and are differentiated based on different antigens associated with their nucleoproteins
What are the key antigen proteins on the surface of the influenza virus. What part do they play in the virus’s entry/exit from the host and in the production of new strains?
Neuraminidase - an enzyme that can cleaves Sialic acid which helps the virus be released by the host (most human and animal cells have this on their surface).
Hemagglutinin - key for binding and membrane fusion between the host cell and the virus particle
Mutations in these proteins are responsible for producing new strains
What happens once the influenza virus enters the body. How does the virus defend itself against the host’s immune system?
- Prefers respiratory epithelium, uses its outer protein to attach to the cell causing a vesicle to form around it called an endosome. The endosome’s change in pH causes the membranes to fuse together - resulting in release of the viral genetic info into the cytosol
- Viral info shuts down the normal synthesis of nucleic acids/proteins and replicates its own
- Expression of viral proteins on the surface of the host
- Through a budding process the assembled virulent particles leave the host cell to infect others. As it detaches it takes some of the host’s membrane to confuse the host’s immune system
- Virus multiples in the ciliated cells of the lower resp tract resulting in functional (mucociliary escalator) and structural (localized inflammation) abnormalities
Name 5 signs/symptoms of influenza and the causative agents. What causes the symptoms?
Signs/symptoms: sudden fever, pharyngitis, congestion, cough and myalgia. Symptoms are produced by the immune response to the virus (not necessarily the virus itself)
Pathogens: influenza virus types A and B
Why are patients with the flu particularly at risk of developing a secondary infection and what are the three bacteria most commonly responsible for causing this?
The initial infection causes gaps in the protective epithelia that provides other pathogens with easier access, making the host more susceptible to secondary infections.
The three bacteria that most commonly cause a superinfection are
- Streptococcus pneumonia
- Hemophilus influenzae
- Staphylococcus aureus
Name and compare the two main processes that mutations in influenza occur
- Antigenic shift; much quicker and can often produce severe forms of influenza. The host may be infected with 2 viruses and its genes become mixed up and antigens from both viruses are produced - creating a novel virus
- Antigenic drift; influenza virus enters host cell and over time a naturally occurring mutation may arise leading to a slightly different version of the virus leaving the host. Process is much slower as it will take time for this virus to become the dominant form
How is influenza treated?
*Include the types of vaccines and how symptoms are cared for
Symptomatic care: 1. Rest and fluid intake 2. Conservative use for analgesics 3. Cough suppressants (and anticipation that there may be complications)
Two types of vaccines
- Trivalent inactivated vaccine (TIV), protection via IgG antibodies
- Live, attenuated influenza virus vaccine (LAIV), provides mucosal, humoral and cell-mediated immunity (given nasally)
Amantidine and rimantadine if the infection has been diagnosed within 12-24 hours.
What kind of virus is Coronavirus and where does it primarily infect? How can it be spread?
Enveloped viruses with a positive sense RNA genome (and a nuclei-capsid of helicopter symmetry). Primarily infect epithelia in the upper respiratory tract and the GI tract. It can be spread airborne or through fecal/oral routes.
