Explain the make-up of a virion.
A genetic core exists which is either DNA or RNA. You can see on Table 34-1 that viruses can be divided into DNA or RNA viruses. The group of nucleic acids surrounded by a protein shell is called a capsid. The capsid can be surrounded by a glycoprotein membrane or envelope which gives you a virion.
Is a virus able to sustain itself without a host?
No a virus does not have cellular organelles necessary to produce proteins etc. so they are dependent on the host cells that they invade. Remember bacteria can produce proteins but they require their nutrition from a host. A virus can then take over and have the host cell produce their RNA/DNA.
How do viruses enter a host cell? Review the information on viral replication so that you can understand how some of the antiviral medicines are designed to work. (Figure 34-2)
A virus will enter by attaching to the membrane and then release its contents into the cytoplasm, or will move into the cell and continue the "uncoating" of its membrane and shell thus releasing the nucleic acids. They then can take over the cells organelles and begin to produce their own proteins.
Eventually their own proteins mature and are released to infect other cells.
Why is it that we may not realize we are sick until there are a significant number of invaded cells in our system?
The above can occur quietly and large numbers of the virus' can be made before we begin to have symptoms.
Why is it then more difficult to destroy a virus compared to bacteria?
Because the virus is within the host cell we don't want to kill the host cells to get to the virus in high numbers. We can't be as selective as you can with the bacteria. Also there may not initially be markers on the outside of the cell that identifies that cell as one that has been taken over. An antiviral drug could not selectively identify the invaded cells only.
We previously talked about taking an interferon for what disease?
What were the major ADR's from taking interferons?
C/O flu-like symptoms.
Scientists first realized these endogenous substances had some significant benefits in minimizing damage from virus' and other rapidly-dividing cells.
What do we know about the action of interferons that can protect cells from the viral invasion?
We know that through interferons the cells tell the neighboring cells: "Put up some protection, I have been infected and you must save yourself."
Review the column on the control of viral infections with vaccines
Virus Vaccines - whole virus or part of a virus that has been completely or partially inactivated - acts as an antigen that induces the immune system to generate virus-specific antibodies
What is an antiviral drug applied topically to treat blisters and cold sores by herpes virus simplex?
How does Abreva work?
Acts on the host cells so that the virus cannot adsorb to the surface of the cell
What limits HIV by inhibiting the abilty of HIV to bind to and enter susceptible host cells such as CD4 lymphocytes?
What is HAART?
HAART - highly active antiretroviral therapy - using at least 3 anti-HIV agents - decreases the viral load (amount of viral RNA present in the bloodstream)
What antiviral decreases viral DNA replication?
What is it used to treat?
How is it applied?
acyclovir [Zovirax] -
• Used to treat herpes-simplex-related infections, genital herpes and infection of the herpes virus family
o Epstein - Barr
• Can be applied topically, oral, or IV MOA
This medicine is taken orally and can be converted to Zovirax in the GI tract and the liver. In this manner more medicine is ultimately absorbed into the bloodstream.
What is Valtrex?
What drugs can be given prophylactically and taken post-exposure to lessen the duration and intensity of the illness to treat Influenza A. How effective are they?
70 - 90% effective.
It is thought to be dual-effective. Being able to inhibit both at an early and a late step of the infection.
*The early stage may prevent the uncoating of the virus as it enters a host cell which can prevent it from replicating within the cell.
*The later step is that is may prevent the reassembly of nucleic acids so that it again cannot continue to increase in numbers.
What are ADR's of amantadine [Symmetrel] rimantadine [Flumadine]?
ADRs - especially in the elderly population - which is a group you would like protect from the flu. ADR include some CNS issues such as: confusion, loss of concentration, mood changes, and an overdose may cause seizures
What drugs are effective in treating Influenza A and B? Similarly to the above medications, the medicine can be taken prophylactically or if taken within 48 hours of the onset of symptoms, can decrease the severity and duration of the flu symptoms.
How are oseltamivir [Tamiflu
zanamivir [Relenza] effective?
by inhibiting an enzyme (neuroaminidase) that the virus uses to complete biosynthesis and release from its host cell. Therefore there is a decrease in the amount of viral replication.
How is Relenza administered? How is this a problem?
Relenza is administered by inhalation. Can cause bronchospasm therefore it is suggested not to be used by patients who have bronchoconstrictive diseases such as asthma and COPD
How is Tamiflu administered? How is this a problem?
Tamiflu is taken orally and the ADR are the typical GI complaints such as nausea, diarrhea, abdominal cramps (my thought: seems to cause a lot of the same symptoms that flu causes - well maybe there is a decrease in the fever, lethargy, achiness, and a decrease in the longevity of the illness.)
(T/F) Antivirals shouldn't take place of flu vaccine.
Antivirals only decrease time you're ill to ______.
What is one possible advantage of antivirals?
Those who are susceptible (already have comobidites, elderly, etc) - decrease severity of illness
When should you start taking antivirals?
Within 48 hours of symptoms
How long should you take antivirals?
take for at least 5 days but can go longer if necessary
If your Dr. doesn't want to prescribe antivirals because you haven't taken the flu vaccine, what is a trick to get it?
1.) Allergic to eggs
2.) Previous complications from the flu vaccine
- Minor complications (nausea)
- Severe complications - (i.e. Guillen-barre)
3.) People who don't have good immune responses from the vaccine (ineffective)