Disease and Immunity

Lecture 1_Topic 1

June 27, 2023, 8:33AM

26m 48s

Naomi Varela 0:04
Disease and immunity, now disease and immunity, can be divided into 5 different topics.

Naomi Varela started transcription

Naomi Varela 0:09
The first of which is going to be looking at pathogens and infectious disease.
So I guess before we can begin, we really need to consider what microorganisms are now.
Microorganisms are organisms that are too small to be seen with the naked eye, which means that we need to use a microscope in order to be able to see them.
Now, some of these microorganisms are harmful, but others are quite beneficial to us.
Our focus, however, is going to be on those microorganisms that are harmful.
Now, microorganisms that are harmful, the ones that cause disease, we call them pathogens.
So from now on, when I refer to the word pathogen, you need to understand that I'm actually talking about microorganisms that cause disease.
There are different types of pathogens.
The first of which we're going to look at are bacteria.
Now bacteria are unicellular microorganisms, which means that they are only made up of 1 cell.
There are also prokaryotic which means that they contain no membrane bound organelles, so their genetic material, the DNA or deoxyribonucleic acid, does not reside within a nucleus.
Bacteria typically range from .2 to 10 micrometres in length, so they're really small.
Like I said before, you need a microscope in order to see them, and they vary in shape so they can be circular, spiral or rod.
The image that you're looking at on the screen is of a rod shaped bacteria.
Now bacteria can reproduce asexually via a process called binary fission, which simply is the bacteria replicating its DNA.
The cell wall dividing and then two bacterium being formed.
Now this process as simple as it is happens every 20 minutes or so, which means you can have exponential growth of bacteria in a very short amount of time.
Bacteria can be found everywhere, from food to really salty environments.
Really hot.
Really cold environments.
Pregnant women are actually cautioned against consuming soft serve or a thick shakes simply because listeria bacteria can be found in the soft serve machines.
And so not only are they advised not to eat soft serve, which really sucks in summer, but they're also cautioned against eating meat such as salami and ham, because again, they also pose very big risk of having high levels of bacteria.
Now this pink lake that you can see in the presentation, that is a really salty lake.
Now, that particular Pink Lake, believe it or not, bacteria can be found there.
It can be found in uncooked meat, and these hydrothermal vents in the image to the right.
Those hydrothermal vents can exceed temperatures of 400 degrees Celsius, and that's because of the geothermal heat generated by the volcanic activity and the interaction of sea water with hot rocks deep beneath the ocean floor.
Now, not only is that particular environment really, really hot, but it's really pressurised as well.
So it's pretty incredible to think that bacteria can be found in those sorts of conditions.
They can also be found, like I said, in really cold environments.
So even in the Arctic umm ice caps, they can be found there too.
Now I'm sure at some point some of you will have picked out some ham or some kind of meat from the fridge and you've touched it and it's felt a bit slimy.
Or it smells a bit funky, or you look at it and it's got this rainbow metallic kind of Sheen glistening from it.
Please, if you ever see here, smell or feel anything like that, please do not eat it.
Do not consume it because you will get food poisoning.
That is a clear indication that your meat has been contaminated or it has growth bacterial growth.
Umm.
And we definitely don't want to get food poisoning.
It's very, very unpleasant.
Viruses are another type of pathogen but they are non cellular so they're not made up of cells.
They do contain genetic material in the form of DNA or RNA, so deoxyribonucleic acid, or ribonucleic acid, and that genetic material is wrapped inside a protein code called the capsid.
Now these capsids can have envelope proteins on the outside or spike proteins and those proteins assist a virus in being able to attach to a cell.
Now varse's are really, really small.
They're only, you know, on average 20 to 400 nanometers in size.
So there's much smaller than bacteria.
They're much smaller than our cells, which means that they can actually infect a bacteria, and that particular type of virus is called a bacteriophage, and they can actually infect our own cells.
And in order for viruses to reproduce, they actually need cellular machinery to do so, which means that they can't reproduce independently.
They have to infect a host cell in order to be able to make copies of itself and then after they've made copies of itself.
It leaves the cell and infects a new cell and does the same thing over and over and over again now.
Viruses, like I said, they're typically found in living organisms because in order for them to be able to reproduce, they need to use the cellular machinery.
But on occasion they can be found.
Umm, you know, outside of a living Organism?
Of course they don't survive too long outside of 1.
Now viruses are responsible for causing a number of different diseases, one of which awards.
There are various strains of the human papilloma Milo virus that affect the skin and mucous membranes causing warts.
Uh.
The the uh bars is also known for causing influenza, which is, you know, the flu.
And as you know COVID-19 as well.
Funky are another type of pathogen.
They are multicellular, meaning that they are made up of more than one cell and their ukyou, which means that their DNA is contained within a nucleus and they do contain other membrane bound organelles.
They do vary in size, so they do have microscopic structures such as spores that are, you know, they're microscopic, so they're very, very small.
But then you can also have fungi that are several meters in length, so you know as big as you know some mushrooms.
Fungi can be found outdoor in soil and plants, and it can be found indoors, on surfaces and in the air.
The thing about fungi is that they love moist and warm environments, so if you have especially a dark, damp, warm environment, chances are you're gonna end up having fungi grow there.
Now, I'm sure you're familiar with this type of funky, which is mold, so if you've had maybe some fruit that has been, you know, hasn't been eaten and it's been left out for a very long time, you might find that there is mold growing on the inside of that.
You'd think, OK, given that fungi do love warm, cold, not cold, but warm, moist, damp environments, how could food go moldy in the fridge?
Like when you look at a punnett of strawberries, sometimes you'll see there's this one strawberry with a little bit of mold on it.
And then next thing you know, the whole Punnett of strawberries is like done.
It's all contaminated.
There's mold everywhere.
How can it survive in such a cool environment?
Well, that's because all it takes is an environment that not only is damp and moist, but if it's got little ventilation, that is also another precursor for mold growing.
All it takes is for you to move that piece of fruit just a little bit and then the spores on the mold will actually transfer to the next piece of fruit.
And that's how you have that spread occur.
Fungi is also known for causing athletes foot, so athletes foot is caused by a fungal infection, which is why when you go to, you know, public swimming pools when you go into the bathroom area and they want you to, you have a shower, you should really be wearing slides or thongs because chances are, given that it's warm, damp and you know sometimes not so well ventilated, chances are there's gonna be umm some kind of fungi in there.
And if you come across it, you can develop that fungal infection.
So it's really, you know, good to take the advice of the businesses that say, hey, if you're gonna have a shower here, please wear slides or thongs.
Now, like I said, you can have mold, but you can also have mushrooms which fall under the Kingdom of fungi.
Now mushrooms.
Some of them are edible and some are not because they either produce hallucinogens or toxins that can cause death.
So Fungy can be.
Umm, you know, pathogenic.
Now when you think about UM, you know pathogens and you think about just how you know the degree of intensity or you know how easy they can cause disease, you know, whether it's through the possession of toxins or enzymes, then, you know, mechanisms to evade detection by the immune system or the ability to invade host tissues and replicate and things like that.
What we're talking about is a pathogens virulence.
So the more virulent a pathogen is, the better it is at being able to produce more toxic enzymes.
And you know, the better it is at evading detection by the immune response, the better it is at invading host tissues and replicating.
OK.
I'll just need you to be aware of that and another the last type of pathogen that we're going to look at are parasites.
Now parasites are unicellular or multicellular, and they're eukaryotic, so again, their DNA is contained within a nucleus, and they also have other membrane bound organelles, such as mitochondria.
Now, parasites do vary in size, and this will depend on the species and the stage of the life cycle that the parasite is in.
Parasites can be found in water in all on hosts.
Now, given that they can survive in or on a host, so they could be an endoparasite being within or an ectoparasite if they're living on the host, they will need to have hooks and claws or suckers to be able to attach to their host.
So this is a characteristic feature of a parasite.
This image here is an image of a parasitic worm, which is an endoparasite is an endoparasite because it lives within the body.
An example of an ectoparasite is this Lyme disease tick that you can see on your screen now.
So I did mention that pathogens are disease causing microorganisms.
So when you're thinking about disease, I guess we need to consider disease as the abnormal condition or change that interferes with normal body functioning and this can cause mental, social or even physical issues.
Now any disease that you think about, umm, it it does need to be diagnosed by a doctor and diagnosis can help you or the doctor treat the disease.
So in order you know, for a doctor to be able to diagnose a disease and treat it, the patient will come in with specific symptoms and particular signs that indicate, you know infection by a particular disease.
Now I did say just then infection by a particular disease, technically that's not correct.
Not all diseases are caused by infections.
Infectious diseases are caused by infection by a pathogen, but there are other types of diseases that you should be aware of now.
Environmental diseases are diseases that result, umm, from pollution and an example of this could be lead poisoning or pesticide poisoning.
Asbestosis, their examples of environmental diseases, social diseases are human induced and examples of this could could be alcohol addiction or drug addiction.
Genetic diseases are caused by genetic abnormalities.
They are inherited diseases that are passed down from one generation to the other, and this could be, you know, Down syndrome or hemophilia.
Of course, there are other genetic diseases, but they're just a couple of examples.
Nutritional diseases are directly caused by or related to inadequate nutrition, and this can include obesity or.
Deficiency diseases such as iron deficiency or vitamin A deficiency.
Degenerative disease.
Is a result of aging and examples of this include multiple sclerosis or osteoarthritis, heart disease, Alzheimer's disease, mental disease is a neurological disease.
So, you know, schizophrenia, depression, anxiety, bipolar, these are all examples of mental disease.
Zoonotic diseases are diseases that are transmitted from animal to human. So.
Mad Cow is an example of that.
COVID-19 is believed to have originated from bats, so given that it originated in bats and has now been passed on to humans, you can consider that a zoonotic disease.
And like I mentioned before, infectious diseases are diseases caused by pathogens.
Now it's important to note that when people have a disease, sometimes they do not display the symptoms and when a person has a disease but does not display any symptoms of it, this can be problematic because one they could be spreading the disease without even knowing.
And worst case, if it's a genetic disease, they could pass the disease on to their offspring or their child and not even realise it's because they've had the genetic disease that has skipped a generation and, you know, been expressed in in their child.
Now people that have a disease without displaying symptoms, we can say that they're either carriers of the disease or they're asymptomatic.
Now, I'm sure you've heard that term asymptomatic when COVID was around and it was really prevalent, you probably would have heard that term a lot, but asymptomatic simply means to carry a disease without displaying any symptoms.
So I guess we need to now consider whether all infectious diseases are contagious.
So I said that there are a number of different type of diseases and in this unit we're focusing on pathogens and infectious disease.
So are all infectious diseases contagious?
The simple answer is no.
Diseases that are caused by pathogens that can easily pass from person to person.
Yes, they are considered contagious.
Example.
Umm you know chicken pox?
That is a perfect example of a contagious infectious disease.
It's caused by pathogen.
It can easily spread from person to person.
Umm.
Diseases that are caused by pathogens that are not able to be passed from person to person easily or at all, then non contagious infectious diseases.
OK, so in thinking about infectious diseases, we need to consider how they spread or what their mode of transmission is.
And this is important because we need to be able to consider how we're going to prevent the diseases from spreading, how we're going to manage the risk of this disease, how we're going to, you know, monitor or surveillance, this disease and minimise the outbreak.
So in looking at modes of transmission or how disease spreads and infectious disease spreads, there are a number of different ways.
So respiratory droplets they when droplets containing infectious pathogens are expelled into the air and this could happen by coughing, sneezing, talking or even breathing.
And then those who you know infectious respiratory droplets, they're inhaled by someone nearby.
So someone who sick could be talking and then, you know, maybe they cough a bit.
And even though you know you might be standing, say, a meter away, that's probably still close enough for you to accidentally breathe in that respiratory droplet.
And for you to now be infected with the disease airborne, that's closely related to respiratory droplets, that's basically where you know the spread of the pathogen through small particles that remain in the air for an extended period of time occur.
Umm, but they just kind of remain suspended there for a bit.
They won't stay there forever, but they'll stay there for a little bit, which was part of the concern with COVID-19.
If people had COVID-19, they were concerned that some particular strains of COVID-19 and had the ability to be able to be suspended in the air for a little bit of time.
Umm, direct contact refers to direct physical contact between an infected person or an animal, and a susceptible individual, whereas indirect contact refers to the spread of a pathogen through contact with a contaminated object or surface, or a vector such as a mosquito or a tick.
Now, in speaking about a vector, a vector is simply an intermediate host, such as a mosquito or a tick.
So when you think about malaria, malaria is a bloodborne, uh disease.
And if a mosquito comes along, uh, bite someone who has the disease, drinks their blood and then makes their way and bites someone else who hasn't been infected before and they're now like, cross contaminating, they're now passing on this bloodborne disease when they inject themselves into the new host.
Who?
They're, you know, trying to take a blood sample from so, you know, a vector is that intermediate host.
You're not coming directly into contact with someone who, let's say, has malaria, but the mosquito has the mosquito has come into contact with someone who has malaria.
It's a bloodborne disease.
The mosquito drinks the blood from that person and then they come to you and try to drink your blood.
But in the process, cross contamination occurs and so now you've now.
Become infected with malaria are foodborne disease.
Pretty self explanatory.
There's pathogens that can be found within food.
Waterborne again.
Pretty self explanatory pathogens that can be found within water.
UM, you know, there's also.
It's not here on the screen, but you can also have fecal oral transmission.
And that simply refers to pathogens that might be in feces of an infected person, and I contaminate the food.
Or or water or even hands.
Umm of someone you know who has somehow come into contact with this?
These feces or poo and haven't washed their hands.
And so now they've touched their eyes or their mouth or nose, and the pathogens been able to gain entry via that path.
So this brings us to our last slide, which simply looks at why it's actually important to understand the mode of transmission or why it's important to understand the way in which an infectious disease spreads.
And it's basically about wanting to interrupt a minimise the spread of disease.
So if we can look at methods to prevent and control.
Umm, you know the spread.
If we can look at targeted interventions that you know, focus efforts on high risk groups and screening and testing and educating and you know awareness campaigns, so that if we can make people aware of how the disease spreads, then we can implement actions you know to minimise the risk of becoming infected, we can look at risk assessment.
We can look at, you know, if you know a community.
UM is infected with a particular infectious disease.
What impact is that gonna have on individuals within that community and in the community as a whole?
What resources are we going to have?
What resources are going to be allocated to which people within the Community?
How is this outbreak going to be managed?
They need to consider, you know, targeted vaccines and treatment and preventative measures.
They need to consider you know.
Surveillance of the outbreak.
They need to be able to identify and trace the source of infection.
Where is this infection coming from?
Where is you know, how is this infectious disease being able to penetrate our community?
How is it able to, you know, gain access to us?
What is this source of infection?
How is it getting here?
You know, umm, you know how big is or severe is this outbreak?
Are their only a few people infected?
Are there a lot of people infected?
I mean, what if some people being infected are asymptomatic like they've really need to, you know, really assess the situation.
So again, why is it important to understand the mode of transmission or the way in which an infectious disease spreads?
Because we really need to consider how to prevent, manage and.
You know, monitor surveillance of the disease itself.
We don't want it getting out of hand.
We want to minimize umm, the risk.
We want to minimise the spread and we wanna get it under control.

Naomi Varela stopped transcription