Chapter 8 Flashcards
What are viruses?
Obligate intracellular parasites
What can the genome of a virus look like?
RNA/DNA, single stranded/double stranded, circular, linear or segmented
What determines a virus’ shape?
By a protein coat and capsid
What is the nucleocapsid?
The nucleic acid contained within the capsid
What is a virion?
The entire viral particle including the host
What is an enveloped virus?
A virus that has an outer layer of lipid around the nucleocapsid.
More susceptible to environmental conditions, bile and acidity than naked virus
What is a naked virus?
A virus that does not have have an outer layer of lipids around the nucleocapsid.
What are some examples of viruses and their corresponding genome?
Influenza virus DNA is segmented
HIV virus has RNA
How can viruses enter the body?
Oral transmission (contaminated food and drink, saliva)
Droplet transmission (inhalation)
Direct inoculation (injections, trauma, insect bites)
Direct Skin Contact
Sexual transmission
Trans-placental
What does it mean when a virus is host-cell specific?
The virus must find a specific cell in the host to attach to and enter to cause infection
What is an example of a host-cell specific virus?
Influenza virus attaches by its haemagglutinin to a glycoprotein (sialic acid) found on cells of mucous membranes and red blood cells. Why only infects respiratory tract.
What are the stages of infection by a virus?
Binds to a receptor on the host cell and enters (envelope joins cell layer?), uncoating (capsid is shed), replication (synthesis of viral messenger RNA, viral protein for new capsids and viral nucleic acid), assembly capsids from around nucleic acid and release
How can the type of virus release affect the virus?
Budding will form an envelope
Cytosis will form no envelope
What occurs when all naked viruses are released from cells?
Death when the cell bursts upon virus release or all vital functions are taken over by the virus.
What is multinucleated giant cell formation? For which viruses does this occur?
Fusion of the plasma membranes of adjacent cells during the absorption phase. Cell content multiplies but cell is not dividing. Herpes viruses
What is malignant transformation? What viruses cause this?
Unrestricted growth and division as caused by certain retroviruses.
Cytopathic effect
What is the cytopathic effect? Which viruses cause this?
Most viruses cause this. The rounding of the cell due to cytoskeletal changes and brown colouring due to overproduction of pigments
What are inclusion bodies? What viruses use this?
Localized areas (vacuums) in cells where virus replication takes place Rabies.
How does no change due to viruses occur? Which viruses do this?
Viral genome incorporates into host genome and remains dormant
Herpes, HIV
What is the general progression of virus infection in the body?
Transmission, viral replication, spread within the body (localized or systemic), host defence systems and persistence
What are some examples of viruses that cause localized infection?
Rhinovirus in the upper respiratory tract.
Hepatitis B virus in the liver
What is an example of a virus that causes a systemic infection? How does it work?
Polio is contracted from the oral/fecal route and then penetrates the small intestine into lymph nodes and then the circulatory system, brain and motor neurons to cause paralysis.
How do the host defense systems attack viruses?
Inflammation, cleaning up cell debris due to Tc cell and phagocytosis.
How do host defenses attack hepatitis viruses (A, B, C)?
Liver damage due to Tc cells attacking the virus infected liver cells and subsequent inflammation.
How do host defenses attack the measles virus?
Rash as a result of Tc cells killing the cells lining surface capillaries and subsequent inflammation.
How can viruses persist?
Proviral formation-dormant stages (retroviruses)
Immune tolerance or ineffective antibodies (virus-Ab complex remains ineffective)
Virus localized in sheltered area like brain
Antigenic shift
Cell to cell spread without contacting immune system cells
Immunocompromised host
What are the types of persistent infections?
Chronic carrier with continual viral reproduction and continuous shedding (HBV)
Latent in the dormant phase (retrovirus, herpes, chicken pox)
How does the vaccinia virus interfere with host defences?
They produce receptors
Coat proteins that bind to and inactivate IL-1
How can viruses interfere with host defences?
Produce receptors for immune system mediators, interfere with antigen presentation, complement pathway or interferons.
How is the cytopathic effect helpful?
Gives you evidence that the host cells contains the target virus.
Diagnosis without directly looking for virus.
How does adenovirus-12 interfere with host defences?
RT and GI, binds to MHC-1 and prevents its migration to the cell surface
How does the herpes virus interfere with host defences?
Binds to and inactivates the C3
How does HIV interfere with host defences?
HIV RNA blocks phosphorylation of an initiation factor required in the interferon pathway.
How can we combat viral infections?
Antiviral agents (must target host cell also and can't distinguish, closely monitor the patient for side effects) Antiviral vaccines Behavioral changes
What are some side effects of antiviral agents?
Bone marrow suppression, renal toxicity
