Acute vs. Persistent Viral Infections: Study with Video Lessons, Practice Problems & Examples

Viral infections are categorized into acute and persistent types. Acute infections, such as influenza and COVID-19, exhibit rapid onset of symptoms and are typically resolved within days as the immune system eliminates the virus. In contrast, persistent infections can last for years or a host's lifetime, further divided into chronic infections, which continuously produce viral particles, and latent infections, where the virus remains dormant and can reactivate later. Understanding these distinctions is crucial for grasping viral pathogenesis and immune responses.

Acute vs. Persistent Viral Infections

This video, we're going to begin our lesson on acute viral infections versus persistent viral infections. And so it turns out that animal virus infections can be divided into two main categories that we have numbered down below, 1 and 2. And the first category is going to be acute infections, and the second category is going to be persistent infections. And so acute infections are going to be infections that are characterized by sudden onset of symptoms, where the symptoms come very quickly, and over a relatively short period of time. Now persistent infections, on the other hand, are going to be infections that are characterized by lasting for very long periods of time, and perhaps even the entire lifespan of the host. And so if we take a look at our image down below, we can get a better understanding of acute versus persistent infections. And so notice that we're showing you this graph here, and on the x-axis of the graph what we have is time. And, notice that we have time in days over here for this portion of the x-axis, and then we have time in months or years over here for this portion of the x-axis. And then on the y-axis, notice that we have the number of virions that are present, or the number of viral particles that are present over time. And so, what you'll notice is that, the purple shaded region of our graph right here is focused on an acute infection. And in acute infection, what you'll notice is that it relatively lasts a short period of time, just a few days at a maximum here. And, what you'll notice is that, the viral particles are only going to be present for a relatively short period of time before the viral particles are eliminated and they go away. Now over here on the right, in the green background, we're showing you a persistent infection. And with a persistent infection, what you'll notice is that the number of viral particles is going to be steadily lasting for long periods of time, perhaps months or even years in some cases. And so we'll get to talk a lot more about acute infections and persistent infections as we move forward in our course. But for now, this here concludes our brief introduction to acute infections, which, again have a sudden onset of symptoms that last a short period of time versus persistent infections that last long periods of time, perhaps the entire lifespan of the host. And so we'll be able to get some practice applying these concepts and learn more as we move forward. So I'll see you all in our next video.

Diseases of short duration frequently followed by long-term immunity are referred to as:

• A. Intermittent infections.
• B. Chronic infections.
• C. Acute infections.
• D. Persistent infections.

Which of the following viral infections is considered an acute infection? (Answer choices show the name of the virus and the time it remains present in the body).

• A. Human immunodeficiency virus (HIV); Remains in body from initial infection until the death of the host.
• B. Influenza virus (flu); Remains in the body for around 14 days.
• C. Varicella-zoster virus (chicken pox):Remains in the body for years or until the death of the host.

Acute Viral Infections

This video we're going to talk more details about acute viral infections. And so recall from our previous lesson video that acute infections are viral infections that have a sudden onset of symptoms where the symptoms appear very quickly and over a relatively short period of time, for example, just a few days. Now acute viral infections result in the release of viruses from an infected host cell during apoptosis, and some of the cells of the host cell will die during an acute infection. However, the host or the human itself may still survive the acute viral infection despite the fact that some of its cells will die. This is because the host cell's immune system can gradually eliminate the virus from the body, again, over a relatively short period of time. Examples of acute viral infections include influenza, which is the flu, poliomyelitis or polio, mumps, and COVID-19 itself, which, of course, the COVID-19 pandemic, is associated with acute infections. If we take a look at our image down below, what you'll notice is we're showing you a graph here of an acute infection.

On the x-axis of this graph, we have time, and notice that the time is in units of days. We're talking about an infection that occurs over a short period of time, just a few days. Over here on the y-axis, what we have is the presence of symptoms and the number of virions that are present. The presence of symptoms is indicated by the dark orange area that you see and then the lighter orange area represents the presence of virions, the presence of infectious particles. Upon being infected by a virus that is going to cause an acute infection, the virus will be produced over a relatively short period of days. At its peak is when you'll have the most amount of symptoms, so the individual will have symptoms here. You can see that the virions or the viral particles will be present from the beginning to the end of the infection. The host cell's immune system is able to basically eliminate the virus. Over a relatively short period of time, just again within just a few days, the entire viral infection can be eliminated. The virus is going to be completely eliminated again after just a short period of time of just a few days and that is what characterizes it as being an acute infection. Being able to recognize this graph as an acute infection could be something that you could be tested on.

This here concludes our brief lesson on acute viral infections and we'll be able to get some practice applying these concepts and then we'll talk more about the persistent infection. So I'll see you all in our next video.

Which of the following statements about acute viral infections is false?

• A. Acute viral infections cause the host organism to acquire long term immunity to the virus.
• B. Acute viral infections are entirely eliminated by the host over a short period of time.
• C. Acute viral infections can remain dormant in the body for years.
• D. Acute viral infections result in cell apoptosis and the release of newly created viruses.

A vaccine to a virus allows the body to be exposed to the virus and not get sick. This allows the body to recognize the virus and better fight the virus if the person does become infected. How would a vaccine help someone deal with a virus which causes an acute infection?

• A. The vaccine could shorten the duration of the viral infection.
• B. The vaccine could worsen the symptoms of the viral infection.
• C. The vaccine entirely stops the virus from entering the cells of the individual.

Persistent Viral Infections

In this video, we're going to talk more details about persistent viral infections. Recall from our previous lesson videos that persistent viral infections are infections that can last for a very long period of time. For example, several years or even up to the entire lifespan of the host. Now these persistent infections that last a long time can be further categorized into 2 groups that we have numbered down below, 1 and 2. The first type of persistent infection that we're going to talk about is chronic infections, and the second type is latent infections. Both of these are persistent infections that last long periods of time. Now chronic infections are going to be characterized by the continuous production of viral particles over long periods of time.

If we take a look at our image down below on the left-hand side, we're showing you a persistent infection that's further categorized as a chronic viral infection. What you'll notice about the x-axis in this graph is that the x-axis can go much longer here in terms of the time. It can go up to several years, lasting a very long time. On the y-axis, we have the presence of symptoms is categorized by the dark orange area, and the lighter orange area represents the number of virions that are present. Upon being infected by a virus that causes a chronic infection, viral particles will start to be produced and then, there may be symptoms for a short period of time, but then the symptoms may go away, and the person may still be continuously producing viral particles. You can see that the viral particles are still being produced at a high level, for many years.

For latent infections, latent infections once again are persistent viral infections; they last a long period of time. However, with latent infections, the virus is not going to be continuously produced. Instead, with latent infections, chromosomes, and it will not be producing viral particles during that time. However, it can reactivate later in life, several years later, causing a productive infection. Productive infections are going to lead to the generation of new viral particles. The viral genome can actually integrate itself into the host cell's eukaryotic chromosome, creating what we call a provirus. A provirus is basically the eukaryotic version of a prophage where, again, the viral genome integrates into the host cell's chromosome. The virus in a latent infection and a chronic infection ultimately is not going to be eliminated as an acute infection would. It's not going to be eliminated from the organism and symptoms can reoccur later in life for a latent infection.

Notice, taking a look at our image over on the right-hand side, we're focusing on a persistent latent infection, viral infection. What you'll notice is, upon being infected by the virus, the viral particles may be being produced, there may be some symptoms, and then ultimately the viral particles may appear to go away, but what's actually happening is the virus genome is integrating into the host chromosome silently. It may remain silent and dormant for several years before it reactivates. The virus reactivates, and the reactivation of the virus several years later can cause the viral particles to be produced. The virus is going to be silent in the host and is going to be reactivated at a later time, and that is what is characteristic of these latent viral infections.

This here concludes our brief lesson on persistent viral infections, differentiating chronic infections from latent infections, and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.

Varicella is an acute infectious disease commonly known as chicken pox. This disease is caused by a DNA virus that causes a moderate to severe body rash that stays dormant in the body after the rash. The virus can be reactivated years or decades later creating a rash known as shingles. What type of infection is occurring when the virus is dormant in the body for years?

• A. Acute infection.
• B. Chronic Infection.
• C. Latent infection.
• D. Transformation into a malignant cell.

Here’s what students ask on this topic:

What are the main differences between acute and persistent viral infections?

Acute viral infections are characterized by a rapid onset of symptoms that appear quickly and last for a short period, typically a few days. Examples include influenza and COVID-19. The immune system usually eliminates the virus within this short timeframe. In contrast, persistent viral infections last for extended periods, potentially for the host's entire life. These are further divided into chronic infections, where viral particles are continuously produced, and latent infections, where the virus remains dormant and can reactivate later. Understanding these differences is crucial for comprehending viral pathogenesis and immune responses.

How does the immune system respond to acute viral infections?

In acute viral infections, the immune system responds rapidly to eliminate the virus. Initially, innate immune responses, including the activation of interferons and natural killer cells, help control the infection. Subsequently, adaptive immune responses involving T cells and B cells are activated. Cytotoxic T cells target and destroy infected cells, while B cells produce antibodies that neutralize the virus. This coordinated immune response typically clears the virus within a few days, leading to the resolution of symptoms. Despite some host cells dying during the infection, the overall immune response ensures the virus is eliminated quickly.

What are some examples of acute viral infections?

Examples of acute viral infections include influenza (the flu), poliomyelitis (polio), mumps, and COVID-19. These infections are characterized by a sudden onset of symptoms that appear quickly and last for a short period, typically a few days. The immune system usually eliminates the virus within this short timeframe, leading to the resolution of symptoms. Understanding these examples helps in grasping the nature of acute viral infections and their impact on the host.

What are chronic and latent infections in the context of persistent viral infections?

Chronic and latent infections are two types of persistent viral infections. Chronic infections are characterized by the continuous production of viral particles over long periods, often years. Symptoms may appear initially but can subside while the virus continues to replicate. In contrast, latent infections involve the virus integrating its genome into the host's chromosome, remaining dormant for extended periods. The virus can reactivate later, causing a productive infection with new viral particles. Both types of persistent infections can last for the host's lifetime, making them distinct from acute infections.

How do latent viral infections differ from chronic viral infections?

Latent viral infections differ from chronic viral infections in their replication and dormancy patterns. In latent infections, the virus integrates its genome into the host's chromosome and remains dormant for extended periods without producing viral particles. It can reactivate later, causing a productive infection. In contrast, chronic infections involve the continuous production of viral particles over long periods, often years, without a dormant phase. Symptoms in chronic infections may appear initially but can subside while the virus continues to replicate. Both types of infections can persist for the host's lifetime.