Characteristics of Infectious Disease

in this video, we're going to begin our lesson on the characteristics of infectious disease. And so it's appropriate to first start off with the definition of disease. And so disease can be defined as a condition that is not the result of a physical injury where the normal structure and function of a host is either damaged or impaired. And the term infection can be defined as the colonization and the replication of a pathogen or a disease causing agent within a host. And so if we take these two terms infection and disease and put them together, we can get the term infectious disease, which can be defined as a spread herbal disease that is caused by an infection that results in the patient showing signs and symptoms. And so it's important to be able to differentiate between signs and symptoms. And so signs can be defined as objective evidence of infection that can be directly observed, measured or detected by another person other than the person with the infectious disease. And so examples of signs include a rash, swelling and fever, which again, are all signs of infection because they can be directly observed, measured or detected by another person other than the person experiencing the infectious disease. Now, symptoms on the other hand, are more so defined as subjective evidence of infection that can really only be experienced by the person with the infectious disease. And these symptoms cannot really be directly observed, measured or detected by another person. Um, and they're only felt again by the person experiencing the infectious disease. And so examples of symptoms include pain and nausea, which again can easily be detected by the person with the infectious disease but cannot be detected observed or measured by another person. And so some diseases are also referred to as asymptomatic diseases. And asymptomatic diseases are diseases that are caused by an infection, but they result in the patient showing absolutely no signs or symptoms of the disease. And so these people that have asymptomatic diseases, they may not feel sick at all. However, they can still contain the infectious agent which can be colonized and replicating within that person and so they can still still be a source of infection for other people. And so, if we take a look at our image down below, we can get a better understanding of the difference between signs and symptoms as well as asymptomatic disease. And so notice over here, on the left hand side, we're showing you a person that has quite a high fever. And so because fever can be measured by temperature and detected by another person, just by using some kind of thermometer, a person with a fever is showing a sign, a detectable sign of infection. And again, signs can be directly observed and measured by another person other than the person with the infectious disease. Now on the right hand side over here, we're showing you a person that is experiencing pain and is feeling nauseous. And so this person that is feeling nausea and pain. Um they are showing symptoms of infection and that's because the pain and the nausea can really only be experienced by the patient with the infectious disease. But they cannot easily or directly be observed, measured or detected. And so these are categorized as symptoms. Now, over here, on the right hand side, we're showing you an example of asymptomatic disease and so notice that this person here is saying that they feel fine and they are not showing any signs or symptoms. However, notice that this particular infectious agent here, which seems to be replicating within their lungs um is still colonized and replicating within this person. And so they still have the disease. They are just a symptomatic with the disease. And so they can still be a source of infection and they can still uh cause other people to acquire the infection. And so some diseases are or can be asymptomatic for some people. And so this year concludes our brief introduction to the characteristics of infectious disease. And as we move forward in our course, we'll be able to learn more about them. So, I'll see you all in our next video

in this video, we're going to differentiate between communicable diseases and non communicable diseases. And so some diseases can actually easily spread from one person to another person, while other diseases cannot spread from one person to another. And so communicable diseases which are also sometimes referred to as contagious diseases or infectious diseases are diseases that can spread between hosts. And so these communicable contagious or infectious diseases are diseases that can easily spread from one person to another person. Now, the term infectious dose is a term that refers to the specific number of microbes that are required to establish an infection in a host. And so a pathogen that has a very, very high infectious dose will only cause disease if the person is exposed to a very high number of microbes, whereas a pathogen that has a very, very low infectious dose can cause disease even if a person is only exposed to a very small number of microbes. And so we'll be able to get a better understanding of communicable contagious or infectious diseases as well as the infectious dose down below on the left hand side of our image when we get there. Now, non communicable diseases on the other hand, are going to be non infectious diseases that do not spread from host to host. They do not spread between hosts or they do not spread from one person to another. And so an example of a non communicable disease would be cancer, for example, which is not a community communicable disease, it is a non communicable disease because cancer does not spread from one person to another. Now these noncommunicable diseases can arise from genetic, physiological lifestyle and environmental factors. And so they're not typically going to result from a pathogen itself. And the communicable contagious or infectious diseases. On the other hand, they typically result from pathogens or disease causing agents. And so if we take a look at the left hand side of our image over here, we can get a better understanding of these communicable diseases or contagious or infectious diseases. And so recall that these communicable diseases can spread from one person to another. And so notice over here we have an unhealthy person that seems to be showing signs and symptoms. And over here we have a healthy person. And so notice that this person that is infected seems to be coughing and sneezing and spreading microbes. And so if this microbe has a very, very high infectious dose, then what that means is that it takes a lot of microbes to make you sick. And so if this person is only exposed to a low number of microbes, then that would not be enough microbes to make this person sick. And so this person would remain healthy if they were only exposed to a low number of microbes when that microbe has a high infectious dose. However, if this person is exposed to a high number of microbes for a microbe that has a high infectious dose, then that would be enough to make this person sick. And so notice here that they have a thermometer in their mouth and they're not feeling very well. And so again, communicable diseases can spread from one person to another. And the infectious dose tells us the specific number of microbes that are needed to make a person sick. Now over here, on the right hand side, what we're showing you is a non communicable disease or a disease that does not spread from one person to another. And so notice that this person over here is smoking uh some tobacco which is gonna have all types of carcinogens and mutations, things that cause uh cancer and mutations and this person loves smoking but smoking can lead to cancer. And so notice that this person over here has developed cancer. And so um cancer is an example of a disease that is non communicable because it does not spread from one person to another. And so this year concludes our brief lesson on communicable versus non communicable diseases. And we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video

Which of the following would be considered a sign of a disease or infection?

• A. Headache.
• B. Pain.
• C. Nausea.
• D. Fever of 39°C (102°F).
• E. Lack of appetite.
• F. All of the following can be signs of disease or infection.

Diseases or infections that can be transmitted from one individuals to another are categorized as what types of diseases?

• A. Symptomatic.
• B. Clinical.
• C. Communicable.
• D. Noncommunicable.
• E. Latent.

Which of the following illnesses is an example of a noncommunicable disease?

• A. Infection with a respiratory virus like the flu or Covid-19.
• B. Food poisoning due to bacterial toxins found in canned food.
• C. Skin infection and blood infection acquired from a dog bite.
• D. Infection caused by an accidental puncture by a contaminated needle.

Pathogens that are very virulent are more likely to cause disease than pathogens that are less virulent (Virulence:the ability of a pathogen to cause and infection/disease). The infectious dose for Virus X is must lower than the infectious dose of Virus Y. Which virus is more virulent?

• A. Virus X.
• B. Virus Y.

in this video, we're going to differentiate between primary infections and secondary infections. And so what's important to note is that an infected person may actually be more susceptible to a second infection and this is because of the damage that's done to their body by the very first infection. And so the very first infection can make a person weaker and more susceptible to a second infection. And so scientists referred to the very first infection as the primary infection. And so the primary infection can be defined as the first or the initial infection that is going to be caused by a primary pathogen such as for example, the virus HIV, or human immunodeficiency virus, which is a virus that attacks and kills human B cells, or b lymphocytes that are part of adaptive immunity. And so primary pathogens such as HIV are capable of infecting even healthy individuals that are not infected and they will do this in a primary infection. Now, the secondary infection, on the other hand is of course going to be a second infection that occurs only after the primary infection. And so this secondary infection is going to be a second infection caused by opportunistic pathogens. And so opportunistic pathogens are pathogens that usually do not cause disease under normal circumstances with a person that has a normal and healthy immune system. However, these opportunistic pathogens, as their name implies, are capable of taking advantage or taking the opportunity to infect a compromised host that may be infected with a primary infection. And so again uh a person is more susceptible to a second infection by an opportunistic pathogen after they are exposed to a first or primary infection. And so if we take a look at our image down below, we can get a better understanding of this idea and how opportunistic pathogens can infect a compromise post. And so the compromised host is going to have a primary infection. And so notice over here, on the left hand side, we have a healthy person that does not have an infection. And so we're going to assume that this person has a normal healthy and active immune system. And so notice that their immune system cells, the B cells and the t cells here are very strong and they are ready to defend off even opportunistic pathogens that may want to try to cause harm or other pathogens that may want to try to cause harm. And so notice that these pathogens over here saying, oh man, we can't fight that because that's a healthy immune system. However, notice over here, on the right hand side, we're showing you a person that has acquired a primary infection such as a person that has the primary pathogen, HIV, which can lead to AIDS acquired immunodeficiency syndrome. And so this is a primary infection and HIV is able to uh cause primary infection even in a healthy person. Okay, But what you'll notice here is that this person has a primary infection and that means that they have a weakened immune system and their weakened immune system makes them more susceptible to a secondary of infection by opportunistic pathogens. And so, whereas before these opportunistic pathogens could not cause harm or disease. Now the opportunistic pathogens are willing to take the opportunity to attack and cause harm when the individual is compromised by the first or primary infection. And so this here concludes our brief lesson on primary and secondary infections, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

Opportunistic pathogens are least likely to infect which of the following groups of people?

• A. Cancer patients.
• B. Drug addicts.
• C. Organ transplant recipients.
• D. AIDS patients.
• E. High school students.

in this video, we're going to discuss virulent. And so the term virulence can be defined as the degree of pathogen is city of an organism or in other words, virulent is the degree of disease production of an organism. How well it can cause disease. And so an organism with very high pathogenesis, ITty is going to be more virulent and that means of course that it is going to be more likely to be able to cause an infection and more likely to cause disease. Whereas of course an organism with a lower pathogenesis, Itty would be less virulent and would be less likely to cause an infection and less likely to cause disease. Now, the virulent factors can be defined as the specific traits that an organism has that allows it to cause disease, or the specific factors that allow it to become virulent. For example, a virulent factor could be a specific gene that the organism has that allows for a toxin production. And this specific gene could be the reason for its virulent or the reason for its pathogenesis ITty. And so if we take a look at our image down below, notice on the left hand side over here, we're showing you some diseased lungs over here that have the bacterium, Mycobacterium tuberculosis, which is going to be the cause of tuberculosis or TB and leads to symptoms signs and symptoms such as chronic cough and coughing up blood, chest pain, weakness, and fatigue, weight loss, uh weight loss and loss of appetite, fever and chills and night sweats. And so mycobacterium tuberculosis would be considered a pathogen that has a high degree of virulent. It's now over here on the right hand side, we're showing you a healthy gut and zooming into the healthy gut which will find is a bacterium called mycobacterium animals. And this bacterium is part of the healthy gut microbiome. And so it is actually a non virulent microbe. And that means that it has a very low degree of virulence, a low chance of causing um infection and disease. And so notice that if this bacteria is an access in the gut, it would only cause things like stomach gas and bloating. And rarely it would cause fever and chills, but it is not going to cause nearly as much as many signs and symptoms of disease as a virulent um pathogen. And so this year concludes our discussion on virulence and we'll be able to get some practice applying these concepts as we move forward in our course. So, I'll see you all in our next video

Characteristics of a pathogen that promote pathogenicity are called:

• A. Pathogen factors.
• B. Colonization factors.
• C. Infectious agents.
• D. Virulence factors.

Virulent pathogens are:

• A. Less likely to cause disease.
• B. More likely to cause disease.
• C. Only able to cause disease in weakened hosts.
• D. Always cause disease whenever inside a host.

Which of the following pathogen characteristics may be considered virulence factor(s)?

• A. Adhesins (molecules that allow a pathogen to adhere to a host cell).
• B. Capsules (protective coatings on the outside of certain bacteria).
• C. Endotoxins (damaging molecules created by certain bacteria).
• D. Proteases (damaging molecules created by certain bacteria).
• E. All of the choices are correct.

An encapsulated bacterium can be a virulent pathogen because the capsule:

• A. Resists phagocytosis.
• B. Destroys host tissues.
• C. Is composed of endotoxins.
• D. The capsule has no effect on the virulence of a bacterium.

Which of the following is a true statement?

• A. A successful pathogen never kills the host.
• B. Throughout disease evolution, the most virulent diseases have spread the fastest.
• C. A successful pathogen does not kill the host before it is transmitted.
• D. The primary goal of a pathogen is to kill the host.