Stages of Infectious Disease Progression - Online Tutor, Practice Problems & Exam Prep

The progression of infectious diseases involves distinct stages: the incubation period, where the pathogen replicates without symptoms; the prodromal period, marked by vague symptoms; the period of illness, characterized by severe symptoms and high pathogen levels; the period of decline, where symptoms and pathogen levels decrease; and the convalescence period, focusing on recovery. Chronic infections may lack a recovery phase, while latent infections alternate between dormancy and resurgence, highlighting the complexity of pathogen behavior and host response in infectious disease dynamics.

Stages of Infectious Disease Progression

In this video, we're going to begin our lesson on the stages of infectious disease progression. And so the progression of an acute infectious disease or a short-term infectious disease actually involves a series of 5 stages that the host may experience. And so notice down below, we have numbered the 5 stages of an acute infectious disease. And notice that below that, we have a graph showing you once again the progression of an acute infectious disease. And on this graph, on the y-axis, we have the number of infectious agents being tracked, and on the x-axis, we have the time as the infectious disease progresses. And so if we take a look at our very first stage of the progression of an acute infectious disease, what we have is the incubation period. And the incubation period is a specific time period between the initial introduction and replication of the pathogen and when the very first signs and symptoms may start to arise. And so this incubation period can take days, weeks, or even years depending on several different factors including the growth rate of the pathogen, the host's conditions including the host's immune system, and the number of infectious agents that the host is exposed to. And so if we take a look at our image down below at this graph, notice that the incubation period is over here on the far, far left of our graph, and it represents a specific time period between the very initial introduction of the pathogen and the time where signs and symptoms may start to arise. And so, that leads us to the prodromal period. So notice that the number of infectious agents in the incubation period is going to be relatively low. Now the second stage of the progression of an acute infectious disease is going to be the prodromal period. And so the prodromal period is actually, an occasional period, that is going to only arise in some circumstances. And so that's why we have that it is an occasional period. And it is defined by early and vague symptoms such as perhaps malaise, which is discomfort, and or headaches. And so what you'll notice is that the prodromal period is right here in this specific region of the graph. And again, the prodromal period is going to precede the period of illness, which is the third stage. Taking a look at the 3rd stage, the period of illness, as its name implies, this is going to be a period where a person may experience the strongest signs and symptoms of the disease. And so if we take a look at our image down below, notice that the period of illness is this region that you see right here. And so, labeling this as the period of illness, notice we have the most severe signs and symptoms, and notice that the number of infectious agents is drastically increasing in this region right here, and the infectious agent is replicating and causing these signs and symptoms. Now, the 4th stage of the progression of an acute infectious disease is going to be the period of decline. And as its name implies, this is going to be where a specific time period where the signs and symptoms are going to start to decline or start to go away. And so if we take a look at our image down below, notice that this period of decline is right here in this region of our graph. And in the period of decline, notice that the number of infectious agents is starting to decrease. And so the signs and symptoms are also going to start to decrease over time. Now the 5th and final stage of the progression of an acute infectious disease is the period of convalescence, And this is going to be the specific period of recovery and recuperation, where the host is actually going to eliminate the pathogen and make a full recovery. And so the host's immune system may still be weak during the period of convalescence as it is recovering. And so that means that it is still susceptible to developing secondary infections even in the period of convalescence. And so if we take a look at our graph down below, notice that the period of convalescence is this very, very last region of our graph. And notice that the number of infectious agents is relatively low, and the pathogen is being eliminated. And so, the host is able to go through a recovery period. And so this here concludes our brief introduction to the progression of an acute or short-term infectious disease. As we move forward, we'll be able to talk about the progression of other types of infectious diseases. So I'll see you all in our next video.

Times and dates of Bob's symptoms of disease: 

• January 7th:Bob is scratched and bitten by a stray dog.    
• January 9th:The stray dog is found dead. Animal control finds that the dog has Yersinia pestis (bubonic plague). 
• January 10th:Bob has fever, chills, and vomiting. 
• January 11th:Bob is hospitalized with diarrhea & has swollen lymph nodes. 
  • Doctors find Bob is infected with Yersinia pestis and give him antibiotics. 
• January 21st:Bob's vitals return to normal and he is released from the hospital. 

Identify the incubation period for Bob's case of the bubonic plague:

• A. January 10th-21st.
• B. January 10th-11th.
• C. January 7th-21st.
• D. January 7th-9th.

Times and dates of Bob's symptoms of disease: 

• January 7th:Bob is scratched and bitten by a stray dog.    
• January 9th:The stray dog is found dead. Animal control finds that the dog has Yersinia pestis (bubonic plague). 
• January 10th:Bob has fever, chills, and vomiting. 
• January 11th:Bob is hospitalized with diarrhea & has swollen lymph nodes. 
  • Doctors find Bob is infected with Yersinia pestis and give him antibiotics. 
• January 21st:Bob's vitals return to normal and he is released from the hospital. 

Identify the prodromal period for Bob's case of the bubonic plague:

• A. January 10th-21st.
• B. January 10th-11th.
• C. January 7th-21st.
• D. January 7th-9th.

Chronic & Latent Infection Disease Progression

In this video, we're going to discuss chronic and latent infectious disease progression. And so in our last lesson video, recall that we talked about the progression of an acute infectious disease or a short-term infectious disease that may only last a few days up to maybe a few weeks. However, here we're going to introduce the progression of a chronic infectious disease. And a chronic infectious disease is a long-term infectious disease that may last up to several years and potentially even the entire lifespan of the host. And so the progression of a chronic or long-term infectious disease is actually characterized by a period of prolonged illness or a prolonged period of illness. And so if we take a look at our image down below over here on the left-hand side, notice that we're showing you a graph that's showing you the number of infectious agents on the y-axis and the amount of time that progresses, on the x-axis. And one thing to notice is that the chronic infection is going to have a progression where it starts off with an incubation period, similar to the acute infection where it's a period, a time period between the introduction of the pathogen and the onset of signs and symptoms. There may be a prodromal period which is going to be characterized by early vague symptoms like discomfort and headaches. And then, there is the period of illness. And notice that the period of illness for a chronic infection is going to be prolonged. And so notice that, it may be prolongeds o much that there is not a convalescence or recovery period, after the prolonged illness. And so, notice here that the number of infectious agents can remain relatively high throughout this entire period of prolonged illness. And the period of prolonged illness may not necessarily have the patient may not have severe signs and symptoms. They may still be asymptomatic, but the number of infectious agents is still going to be relatively high. Now on the other hand, the progression of a latent infectious disease, which a latent infectious disease is a reoccurring infectious disease, is characterized by periods of latency and a period of resurgence. Recall from some of our previous lesson videos that we've discussed latent infections before, specifically when we discussed viruses. And so recall that latency is a state where an infection is going to be in a dormant or inactive or hidden state. And so the number of infectious agents is going to drastically decrease, and it may appear that the infectious agent is completely gone. However, it's not gone. It's just in a dormant, inactive, or hidden state. And so after the period of latency, there can be a period of resurgence when there is a latent infectious disease. And the period of resurgence is going to be a period after the latent state where the infectious agent may reactivate or return and begin to replicate once again. And so if we take a look at our graph over here on the right-hand side, what you'll notice is that we have, again, the same stages of the progression, including the incubation period, the prodromal period, the period of illness, the period of decline, a period of convalescence, and then notice that for a latent infection, there's going to be a period of latency. And in this period of latency, notice that the number of infectious agents is very, very low, perhaps at nondetectable levels. And after this period of latency, which may last up, you know, different amounts of time, it could last up to several years potentially in some cases, there can be a period of resurgence. And the period of resurgence would allow the infectious agent to replicate once again and resurge and basically return and begin to replicate once again. And that again can lead to signs and symptoms arising once again. And so this year concludes our brief discussion on chronic and latent infectious disease progression, and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Most individuals become infected with varicella zoster virus (VZV) during childhood which results in a disease commonly known as chicken pox. After the individual recovers from chicken pox the virus remains dormant in their body. This virus will commonly re-emerge when the individual reaches an advanced age and cause a disease commonly known as shingles. The shingles disease is what stage in the disease progression of the varicella zoster virus?

• A. Period of latency.
• B. Period of illness.
• C. Period of decline.
• D. Period of resurgence.

Individuals infected with human immunodeficiency virus (HIV) begin to show flu-like symptoms 2-4 weeks after infection. During this period, HIV is rapidly multiplying in the body. HIV will continue to slowly multiply within infected individuals for the remainder of their lives (although this can be lessened with antiretroviral therapy). HIV is an example of what type of disease?

• A. Latent infectious disease.
• B. Opportunistic infectious disease.
• C. Chronic infectious disease.
• D. Noncommunicable infectious disease.

Here’s what students ask on this topic:

What are the stages of infectious disease progression?

The stages of infectious disease progression include the incubation period, prodromal period, period of illness, period of decline, and period of convalescence. The incubation period is the time between pathogen introduction and the onset of symptoms. The prodromal period involves vague symptoms like malaise and headaches. The period of illness is marked by severe symptoms and high pathogen levels. During the period of decline, symptoms and pathogen levels decrease. Finally, the period of convalescence is the recovery phase where the host eliminates the pathogen and regains health.

What happens during the incubation period of an infectious disease?

During the incubation period of an infectious disease, the pathogen replicates within the host without causing any noticeable symptoms. This period can vary in length, lasting from days to years, depending on factors such as the pathogen's growth rate, the host's immune system, and the number of infectious agents. The incubation period ends when the first signs and symptoms of the disease begin to appear.

How does the progression of chronic infectious diseases differ from acute infectious diseases?

Chronic infectious diseases differ from acute infectious diseases in that they have a prolonged period of illness that can last for years or even the host's entire lifespan. Unlike acute infections, which typically progress through all five stages (incubation, prodromal, illness, decline, and convalescence), chronic infections may not have a clear recovery phase. The number of infectious agents remains relatively high throughout the prolonged illness, and symptoms may be less severe or even asymptomatic.

What characterizes the period of convalescence in infectious disease progression?

The period of convalescence is characterized by recovery and recuperation. During this stage, the host's immune system eliminates the pathogen, and symptoms gradually disappear. However, the immune system may still be weak, making the host susceptible to secondary infections. This period marks the final stage of the infectious disease progression, where the host regains health and normal function.

What is the difference between latent and chronic infectious diseases?

Latent infectious diseases are characterized by periods of dormancy and resurgence. During latency, the pathogen is inactive or hidden, with very low or undetectable levels. This can be followed by a period of resurgence, where the pathogen reactivates and symptoms reappear. In contrast, chronic infectious diseases involve a prolonged period of illness without a clear recovery phase, with the pathogen levels remaining relatively high throughout. Chronic infections may last for years or even the host's entire lifespan.