Microbiology, part 48: Acellular Infectious Agents - Viral Infections & Viral Growth Curve
Acute vs. persistent viral infections, latent vs. chronic viral infections, the viral growth curve and its different phases (inoculation, eclipse, burst, burst size).
Full Transcript: Microbiology, part 48: Acellular Infectious Agents - Viral Infections & Viral Growth Curve
Full Transcript: Microbiology, part 48: Acellular Infectious Agents - Viral Infections & Viral Growth Curve
Hi, I'm Cathy with Level Up RN. In this video, I will be discussing the key types of viral infections as well as the viral growth curve. At the end of the video, I'm going to give you guys a little quiz to test your understanding of some of the key facts I'll be covering, so be sure to stay for that. And if you have our Level Up RN microbiology flashcards, be sure to pull them out so you can follow along with me. And of note, our flashcards are also available in digital format via Flashables.
With an acute viral infection, there is typically a rapid onset of symptoms, a short duration of illness, and the body's immune system is able to eliminate the virus. However, with a persistent viral infection, the virus remains in the tissues and organs of the infected individual causing a latent or chronic viral infection. With a latent viral infection, the virus remains dormant or hidden in the body cells. And when the virus is dormant, it does not replicate and does not cause symptoms.
So an example of a virus that can cause a latent infection is the Varicella zoster virus, which causes a chickenpox infection. So after a chickenpox infection, the virus goes and hides in the sensory nerve ganglia where it remains dormant. But then it can be reactivated years later causing shingles. With a chronic viral infection, the virus is actively replicating, and symptoms are recurrent or persistent over a long period of time. In some cases, a chronic viral infection can occur after a period of latency. Examples of chronic viral infections include HIV and hepatitis C. The good news is that HIV can be treated with antiretroviral therapy, which can bring the viral load down to an undetectable level. And hepatitis C can now be treated with antiviral medications, which can cure the infection in most individuals.
Next, we're going to take a look at the viral growth curve, which measures viral replication over a period of time. To create this curve, scientists infect a cell culture with a virus and then measure the viral titer, meaning the number of viral particles in a medium at regular intervals. During the inoculation phase, virions, meaning virus particles found outside of a host cell, attach to the cells. During the eclipse phase, viruses enter the host cells and start to replicate. So virions are no longer present in the medium. Then we have the burst phase, which is where newly created viruses are released causing lysis of the host cells.
Our cool chicken hint to help you remember this phase is that during the burst phase, cells are bursting open and viruses are released. The burst size is the number of virions released per infected host cell. This number can vary widely from 20 to over 1,000 depending on the type of virus.
All right. It's quiz time, and I have three questions for you.
Question number one. With a blank infection, the virus remains dormant in cells and does not replicate.
The answer is...latent.
Question number two. Viruses enter the host cells and are no longer detectable in the medium during which phase of the viral growth curve?
The answer is...the eclipse phase.
And question number three. Host cells lyse and viruses are released during which phase of the viral growth curve?
The answer is...the burst phase.
All right. That's it for this video. I hope it was helpful. Take care and good luck with studying.
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