Chapter 9 Flashcards
List the three primary methods for controlling viral diseases.
- Prevent transmission/entry into animal
- Vaccinate
- Use antivirals
What are the two types of whole viruses?
live and inactivated
What is a live vaccine?
a vaccine with containing a replicating, infectious virus
What is an inactivared virus?
a killed virus, partially purified supensions of virions, inactivated by chemical or physical treatment
What is the goal of vaccination?
to prevent or reduce disease, not necessarily to prevent infection
What are the 4 different subcomponents of viruses that are used in vaccines?
protein subunit, virus-vectored, virus like particle, DNA
What is a virus-vectored subcomponent?
a virus, such as vaccinia virus, that is used as an in vivo vector for the gene specifying the protective antigen
What is a virus like particle?
a particle comprised of viral proteins assembled in a virion-like structure
What DNA is used in viruses?
Purified DNA that codes for a protective antigen
What are virulent live virus vaccines?
vaccines that produce planned infections where animals are infected at an opportune time or are injected into a non-critical site where lesions are acceptable
What is the most common form of live virus vaccines?
avirulent/attenuated live virus vaccines
Where do naturally occurring avirulent strains come from?
they may be from the same host, or a closely related by heterologous host
What is an example of a vaccine that came from naturally occuring avirulent strain?
the cowpox vaccine against smallpox
What is the goal of experimentally attenuated strains?
to produce a virus with reduced virulence, but which still retains its original ‘protective antigens’ and is capable of replicating sufficiently in the host to stimulate an adquate immune response
What are empirically-derived mutants selected for?
chance mutations
What are temperature sensitive -or cold adapted mutants selceted for?
mutants with skewed temperature preference
What are viruses that have temperature sensitive mutants forced to do?
adapt to lower temperature by repeated passage in vitro thus they lose the ability to replicate at normal body temperatures
What knowledge is required to generate a genetically engineered mutant?
which genes control the virulence of the virus
What are inactivated whole virus vaccines?
virulent virus grown in cell culture or embryonated chicken eggs is usually partially purified and then inactivated and packaged as a vaccine
What problems are associated with inactivated whole virus vaccines?
proper inactivation is difficult, they are expensive, multiple doses are needed
What are protein subunit vaccines composed of?
individual protective protein subunit of the virion that will stimulate immunity
What are purified subunit vaccines?
vaccines obtained by purification procedures from degraded whole virus
What are closed subunit vaccines?
where recombinant DNA technology used to express a cloned gene coding for a protective antigen in an in vitro expression vector
What are synthetic peptide vaccines based on?
amino acid sequence of the protective antigen
How are synthetic peptide vaccines produced?
by chemically synthesizing a peptide in a machine from amino acid sequences
What problems are associated with synthetic peptide vaccines?
no glycosylation, poorly immunogenic
What are virus-vectored vaccines made by?
inserting genes for the protective antigens into another virus, so that that virus will infect the natural host and serve as a ‘vector’ for expression of the inserted genes within the animal
What are the four advantages associated with virus-vectored vaccines?
- Not possible to revert to virulence 2. Protective antigens from several pathogens can be inserted into one vector 3. Relatively inexpensive to produce 4. Pox virus vectors are relatively stable
What is the biggest single concern associated with virus-vectored vaccines?
the biohazard potential to the vector itself
What is the difference between a virus like particle and a virus-vectored vaccine?
they morphologically resemble the actual virus and induce neutralizing antibody, but they do not have the nucleic acid
What are the three main areas of concern when dealing with vaccines?
effectiveness, safety, and stability during storage
How can a DNA vaccine be used to yield a protein antigen?
sufficient DNA gets into cells and is expressed by the cell to produce immunizing amounts of protein antigen of the pathogen
List five advantages for use of a replicating viral vaccine.
- Replicating agents yield greater antigenic mass because of amplifying effect
- More natural presentation of viral antigens
- Spreads over mucosal surfaces during replication better than non-replicating products, thus stimulating greater mucosal immunity
- Replicating vaccines generally stimulate longer lasting immune responses - a single dose is often adequate
- With live products, immunization of unvaccinated herd-mates can occur
What is a minor problem to bear in mind about replicating viral vaccines?
interference by intercurrent virus infections
What are some potential hazards of replicating viral vaccines?
insufficient attenuation, reversion to virulence, danger to pregnant animals, spread to other animals from shedding, live viral contaminants
What are three benefits of antiviral drugs?
- They can prevent an infection, or stop an infection after it has started
- Provide therapeutic option for those already infected
- Serve as a second arm of defese against virus infections for which vaccines are not available or are not effective
List 5 factors that contribute to the limited repertoire of effective antiviral drugs.
- Challenge of developing drugs that are safe and have high potency
- Specificity of viral agent
- Variable patterns of infection
- In vitro replication
- Cost
What is the mechanism of action of oseltamivir?
blocks the binding of neuraminidase to Sialic Acid
What is the mechanism of action of Acyclovir?
it blocks DNA replication of the virus
What is Acyclovir highly effective against?
herpes simplex
What type of drug is Acyclovir?
a prodrug
Acyclovir has no effect on what?
non-infected cells
What is AZT’s mechanism of action?
to block reverse transcription
AZT was the first antiviral licensed to treat what?
HIV-1
What are drawbacks to AZT?
Competes with thymidine for formation of NTP, short half-life, there are more effective anti-retrovirals (used mainly as a prophylactic)
