The capacity of an infectious organism to cause disease.
Virulent viruses cause significant disease.
Also called 'attenuated'
It's possible that at one point it was a virulent virus but it’s been killed, perhaps a specific gene or the receptor has been knocked off and taken away its virulence but it can’t actually do anything. But if attenuated virus is inside,immune system will still be able to see it and will ammount an immune response
What are the three types of vaccines?
Live attenuated vaccine: made of intact virions rendered non-infectious
Inactivated or killed vaccine: composed of killed or dead virions
Subunit vaccine: composed of immunogenic parts of virions.
Antigen is administered and causes the onset of the immune response
A preformed antiviral product, such as antibody, is administered.
Virus finds specific tissue that it needs. This is good b/c virus has to find the right organ and if it doesn’t find the organ before the immune system finds the virus, the virus will die and immune system will clear it.
Explain Fig. 12
Shows how viruses can be disseminated by blood "hematogenous disemination"
There is replication of virus at initial entry point, then high amounts of virus get into the blood (viremia).
If virons continue to multiply in the blood it's called active viremia
From this point they can move into other areas like muscle and organs, then secondary viremia (so they travel back through the blood and multiply, etc) and then travel to further places to infect more organs, etc.