Describe the structure of a virus.
- ) Nucleic acid (could be DNA or RNA)
- ) Surrounded by a protein coat (capsid)
- ) Lipid envelope (sometimes.
What is a capsid? What are its components?
Capsid is the protein shell that encases viral nucleic acid. It is composed of capsomeres held together by non-covalent bonds.
What is the envelope of a virus composed of and from where does it originate?
The envelope is usually composed of a lipid bilayer with glycoproteins present on the surface.
It’s derived from the host cell.
Pleomorphism
The ability of some viruses to alter their shape or size
Identify and describe the steps in the replication cycle of a virus.
- Attachment - virus attaches to host cell.
- Penetration - Virus penetrates the cell membrane of the host cell.
- Uncoating - the virus injects its nucleic acid into the host cell (not the capsid).
- Synthesis of viral nucleic acid and protein
- Assembly and maturation
- Release in large numbers - this usually results in death of the host cell.
What are the impacts of viral replication on the host cell (4).
- ) Cell death (via lysis, alteration in cell membrane, apoptosis).
- ) No apparent change - latent, persistent or chronic infection
- ) Transformation of cell to malignant cell.
- ) Fusion of cells forming multinucleate and later hybrid cells (after mitosis).
What is ICTV?
International Committee on Taxonomy of Viruses (ICTV) is the only body charged by the International Union of Microbiological Societies with the task of developing, refining, and maintaining a universal virus taxonomy.
What considerations are made when classifying viruses?
- ) Nature of the virus genome and virus genetic diversity
- ) Virus replication strategies
- ) Virus morphology.
Describe serial passage of viruses to create live-attenuated virus vaccines.
This involved placing the virulent virus in an environment it will survive, but not thrive. Collecting it from that environment and placing it into a new environment in which it will survive, but not thrive. After repeating the process several times, the bacteria will mutate for its own survival and those mutations also end up reducing virulence its original host acting as a vaccine rather than a pathogen.
What are non-replicating virus vaccines?
Vaccines produced from inactivated viruses OR parts of viruses.
What are recombinant vaccines?
Vaccines produced by either mutating the virus so it’s genetic composition is severely altered OR subunit vaccines in which a small chunk of viral protein or nucleic acid is introduced to the host. This alerts the immune system with an idea of what the pathogen looks like without risking virulence.
Define pathogenicity
the ability of a virus to cause disease in a host
Define pathogeneis
the mechanism of development of a disease
Define virulence
a measure of the degree of pathogenicity of the infecting virus
Define Lethal Dose (LD50).
The dose of the virus required to cause death in 50% of animals.
Define Primary Viremia
Initial entry of virus into the blood. This may occur by the spread of infection into the blood or direct injection into the blood via arthropods, needles, etc.
Define Secondary Viremia.
Virus has replicated/multiplied in major organs and once more entered the circulation.
Define Disseminated Infection
Infection spreads beyond the primary site of infection
Define systemic infection.
a number of organs or tissues are infected.
Define neurotropic virus
viruses that can infect neural cells. (Infection may occur by neural or hematogenous spread
Define neuroinvasive virus
viruses that enter the CNS after infection at a periopheral site
Define Neurovirulent virus
viruses that cause dz of nervous tissue, manifested by neurological symptoms and often death.
What role do trafficking monocytes play in viral infections?
They can transport viruses - especially when crossing the blood-brain barrier.
Define tropism.
The specificity of a virus to a particular host tissue.
