welcome back in today's lecture we will be covering principles of disease and epidemiology so let's go ahead and get started with today's material symbiosis means life together symbiosis essentially is the relationship between normal flora and the host okay so let's go over a few of these terms and define them commensalism the different categories of symbiosis are commensalism mutualism and parasitism commensalism refers to one or refers to one organism benefiting while the other is unaffected okay so here we see that in commensalism the organism the micro organism has a positive effect but it doesn't affect the host what are some examples well we have microorganisms on the surface of our eyes that don't affect us as well as the external genitalia the micro organism benefits but they don't harm us we're not affected by the micro organisms being in those locations mutualism or mutualistic relationship the micro organism and the host both both benefit from that relationship so both organisms benefit what are some examples of this well in the large intestine ecoli resides we have E coli that resides in the large intestine and it actually provides nutrients for the e coli well what do we get in return in exchange Eco light will actually synthesize vitamin K and vitamin B that are absorbed into the bloodstream for our body to use yeah so that's why we have this mutualistic relationship with e.coli now there is different strains of E coli and so that's a whole other story now the final category here of symbiosis is parasitism and in parasitism we see one organism benefiting at the expense of the other yeah so how does it benefit the microorganism here benefits by driving nutrients and often times can cause disease right at our expense so deriving nutrients and we don't get anything out of it actually it hurts us so that would be an example of parasitism here we go again normal flora what is normal flora or normal microbiota well by definition it's going to be microorganisms that as you know they colonize but do not necessarily cause disease under normal conditions remember that I've mentioned that the micro organism given the opportunity can cause disease right but normal flora again under normal conditions do not what they do do is provide protection they protect us by microbial antagonism or competitive exclusion which basically means that they basically they benefit us by preventing the overgrowth of other microorganisms that could be harmful to us now how do they do that they do that by taking up space by taking up nutrients so there there isn't as many nutrients available for other microorganisms they also can produce their waste products can be toxic for other microorganisms so this is how they can actually provide protection to us for example today we're going to be going over various definitions and we need to go over some of these so that we can understand the various principles of disease so let's go ahead and begin with pathology what is pathology it's a scientific study of disease and etiology is what what is the cause of the disease and so then we move on to pathogenesis which is the origin and development of disease you know that virulence has to do with how dangerous the microorganism is for example and the degree of pathogenicity oftentimes has to do with the virulence factors that the microorganism can have so these are gonna be molecules that are produced by the pathogen or the microorganism that allows it to thrive can you think of any virulence factors just off the top of your head the microorganism can possess that protect it and by protecting itself allows it to thrive and cause infection hmm how about a capsule formation is that a virulence factor how about the ability of the microorganism to produce various toxins yeah those are all variance factors so ideology of infection how is the ideology of infection determined nowadays you have to think way back to the beginning of the semester Koch's postulates the postulates is how we determine and yeah there are some difficulties some microorganisms can be difficult to culture so they that would provide some issues for sure right yeah absolutely all right let's move on continuing on with definitions here principles of disease colonization versus infection what is a difference colonization refers to the presence and growth of an organism without having any observable clinical signs or immune reaction there are some people that are carriers right of various microorganisms but they themselves that are pathogens mind you on the average individual but they themselves do not exhibit any does any observable clinical signs of infection Marrissa for example what does that stand for methicillin-resistant Staph aureus a common sight has been found to be in patients and employees nose right now because the colonization is the presence or growth of an organism without any clinical symptoms right whereas an infection is going to be an invasion of bacteria in the tissue with replication of the organism and an infection will indeed be characterized by clinical signs of illness and this can be characterized by blood counts right you can have a high white blood cell count it can be characterized by inflammation by fever so there are definite signs and symptoms of disease okay so an infection and a disease goes hand-in-hand there right the next one is disease signs and disease symptoms well disease signs are what's discovered by the physician and the symptoms are what's reported by the patient whereas a disease syndrome now is an association of both signs and symptoms okay and finally what is the difference between a primary infection versus a secondary infection the primary infection is usually an acute infection that causes that initial illness right the secondary infection is an infection that occurs during or after the treatment of another infection or that first infection yeah so primary infection is an acute or initial illness secondary infection is going to be an infection that occurs either during or immediately after the treatment of another infection or a primary infection continuing on with principles of disease what is a the difference between the primary pathogen as opposed to an opportunistic pathogen the primary pathogen causes disease just by its sheer presence within a normal healthy host okay so the primary pathogen it's a pathogenic organism that by you being introduced to it causes infection causes disease whereas an opportunistic infection is an organism that does maybe perhaps doesn't necessarily cause disease and infection but in a patient with a depressed immune system will cause disease what does I mean well opportunistic pathogens take advantage of patients that are immunocompromised they have depressed resistance okay and there goes our next word what is an immunocompromised hosts an immuno compromised host is someone that has a depressed resistance their immune system is not as vibrant and very end and you know active as somebody who is has their cellular and humoral immune system working 110 percent right okay let's move on continuing on with our definitions here occurrence as it relates to occurrence of disease when we're talking about occurrence of disease we often talk about the incidence versus the prevalence now what does that mean to understand disease we should know something about its occurrence the incidence of disease refers to the number of people in a population who develop the disease during a particular time so when we look at that it has to do with the number of cases over the number of people at risk whereas the prevalence of disease is the number of people in a population who basically develop the disease at a specific time regardless of when it first appeared so in other words it accounts for both old and new cases over the number of people at risk okay endemic refers to a disease that is constantly present in a population can you think of a disease that is endemic how about the common cold whereas an epidemic is when many in a given area acquire certain disease in a short period of time can you think of things that are epidemics well influenza right the flu aids can be considered an epidemic or how about cope in nineteen Khurana virus yeah and then pandemic is going to be an epidemic disease that occurs worldwide can you think of any pandemic disease that's right Cobin 19 coronavirus right as well as eight a disease outbreak is just that you have these little outbreaks that occur usually locally here we look at when we look at the duration of disease we characterize it by being acute or chronic or latent an acute disease is going to develop rapidly but it lasts a very short period of time whereas a chronic disease develops slowly the reaction is less severe but it can last a long time and then finally alene disease is where the causative agent remains inactive for a while and then reactivates and this is what we see with shingles as a result of a previous chickenpox infection okay now there are some that are some individuals that are disease carriers or what we refer to as having a subclinical infection so these are individuals where the having the microorganism in them the pathogen need the organism does not cause any noticeable illness no noticeable illness and we see this with poliovirus and some individuals even hepatitis A so these can be carried by people who actually never develop the illness very interesting extent of fection infection can be a local infection meaning that the microorganism is limited to a small area such as we see with the boil or an abscess a systemic infection however is when the microorganism spreads throughout the body and usually this occurs via the blood or lymph like we see with measles now when we have an infection in the blood we actually use the suffix emia so bacteremia refers to what do you think that's right bacteria in the blood viremia refers to virus in the blood toxemia refers to toxins in the blood and then finally what do you think septicemia is it's essentially blood poisoning okay progression of disease this is a nice graph that shows you the progression of disease during your initial exposure to the microorganism we start with the incubation period right the microorganism is establishing itself and the in inside your body or whatever then you begin this promise stage you begin to have signs and symptoms of infection maybe malaise you might start developing a little bit of fever and then at the height of infection you have full-blown illness maybe you're coughing you have high fever your body is really just you know in and a lot of pain and then you go through this convalescence period where you are starting to recover from your illness right so that's usually the progression of disease when you look at this table here this graph here when do you think that you are infectious take a look at that you think well you probably are thinking well you would be the most infectious at the height of infection correct yeah probably you're actually infectious throughout every single stage even during the incubation period and during the convalescent period although you are recovering you are so contagious so many people say oh I'm you know I'm not sick anymore and you're hacking away well you probably are still a little infectious okay let's move on disease reservoirs what is a reservoir it's going to be the source which harbors disease-causing organisms right and so these are basically are going to serve for potential disease outbreaks and humans are the most common source the most common source for harboring all these microorganisms we're probably the best reservoir for many microorganisms now we can be symptomatic reservoirs which means that we have signs and symptoms of infection or we can be asymptomatic meaning that we harbor these organisms but we don't show any signs and symptoms of disease so human is probably the most common reservoir for diseases for various microorganisms but there are also non-human reservoirs there is now when the animal is a reservoir we refer to this as a zoonotic infection or zoonosis okay that's referred to as zoonosis environmental reservoirs also exist and we see this in soil and water so here we see you know these this couple is going out for a hike humans being the most common reservoir but so is their dog and look at this little mouse oh my goodness there's some serious diseases cost that are spread through these little mice okay transmission of infectious disease communicable disease is going to be an infectious disease coming from another infected host either directly or indirectly what would be some of communicable diseases well influenza herpes tuberculosis coronavirus right now when that communicable disease is easily transmitted between hosts as is the case with chickenpox and with measles we call this contagious a non communicable disease is going to be a disease that is not spread from one host to the other can you think of any non communicable disease tooth decay is a non communicable disease cancer acme yeah those are all non communicable diseases moving on with contract contact transmission rather so this is how you can transmit various infections you can transmit infection directly through contact or it can be in direct contact via of foam I what is a for might a for might is an inanimate object right so that would be like a door handle a tabletop and then there is also a droplet transmission you sneeze you call if you laugh you're talking and you can transmit droplets that may Harbor some micro that may have some microorganisms in them and transfer them to other so here we see communicable infectious diseases can be transferred or transmitted from one person to the other by direct contact via all these different means whether it's contact through kissing droplets vertical etc or it can be indirect indirectly transmissible the via fomites through food and water you you eat contaminated food because someone that cooked your food to not wash their hands after going to the bathroom droplet nuclei that you can aerosol eyes etc okay or the feces of mice which we'll talk about transmission of infectious disease vehicle transmission this can be through the water transmission of infectious diseases can be transmitted through contaminated water can you can transmitted through contaminated food it can be airborne via droplet nuclei you see here when someone sneezes those droplets can be projected up to or past three feet so that is a lot of area that is a lot of area that it covers mechanical vectors are going to be means by which microorganisms can be transferred from one place to the other and yes flies are great mechanical vectors you're having a barbeque you have your dog in the backyard everything is beautiful right here comes a fly on the poo from the dog right that's the dog feces on the grass then it happens to fly by and lands on your burger you don't notice it or your hotdogs and guess what it just transmitted it hmm possibly microorganisms right yeah biological vectors are going to be microorganisms that replicate within the vector and we're going to talk about that coming up very soon and this is when microorganisms can actually replicate inside maybe in the gut of this mosquito for example and then what happens is that the mosquito bites you and transmits that pathogen to you no sir corneal infections are your hospital acquired infections this is a big problem in hospitals it affects up to 15% of hospital patients cost a lot of money results in a lot of deaths and the number one reason to prevent nosocomial infections is hand-washing so what does it mean a nosocomial infection it means basically that you go into the hospital for one thing and while you're there you catch something else hopefully you come out okay right so it's a hospital-acquired infection you didn't go into the hospital for that reason because you had that infection but you acquired it while you were in the hospital and when we look at the various sources for these nosocomial infections oftentimes it's the patient's own flora oh my goodness normal flora I thought it was there to protect me yes it is but remember what I told you any microorganism given the opportunity will cause disease will cause infection even if it's your own flora if it is misplaced if it's misplaced right other sources of these nosocomial infections can come from other patients maybe the hospital environment healthcare workers if they were carriers right remember what I told you patients and and health care workers can carry mersa and their nostrils not even know it they don't show any signs and symptoms of infection methods of transmission can be through devices personnel airborne this table is not from your book but if you take a look at this you can see the most common type of nosocomial infection is going to be UTIs urinary tract infections why because of catheterization so this is a great example of a misplace microorganism the genital urinary area has a lot of microorganisms a lot of normal flora but the bladder is a sterile site so if you get one of those accidentally in there boom you have an infection now we're shifting to emerging diseases in actually emerging infectious diseases and what this all means prior to the 1980s we actually believed that we basically had conquered infectious diseases by antibiotics the vaccines that we had and better standards of living right but then we had heat in the early 80s and boy did that just hit us like where did that come from right we also started seeing increased antibiotic resistance in Staphylococcus and Mycobacterium tuberculosis we saw outbreaks happening what is in E I D emerging infectious disease it's an infectious disease whose incidence has increased in the past twenty years and not only that not only has it increased in the past twenty years but it threatens to increase even further in the near future as we see with SARS right that's a form of current virus and eight natural evolution of microorganisms is something else to consider the natural evolution of them Vibrio cholerae oh 139 forms the capsule we didn't see that before this emerged in epidemic proportions in India and Bengal Bangladesh looks like well where did that come from the avian influenza h5n1 endemic and many bird populations in Southeast Asia environmental factors climate fluctuations and changes after El Nino we saw a rise in hantavirus we're going to talk about hantavirus very soon but it's not a fun disease to have so what are some of these factors that contribute that contribute to these emerging infectious diseases human contributions for sure complacency and breakdown in our system in a public health system changes in our behavior population expansion etc factors that also contribute is going to be excessive and inappropriate use of antibiotics we are prescribing antibiotics for viral infections even though we know that they don't work for viral infections but patients plead with their doctors because they know that they'll feel better well of course they're gonna feel better after taking them it would have happened anyways natural progression of disease eventually you get better and the increase in antibiotics added to animal feed does not help us the availability of antibiotics with our prescription does not help us people crossing the border either to Mexico or Canada to acquire antibiotics without prescriptions that doesn't help us right increasing population of immunosuppressed patients we have great drugs we have successful trance transplants all those patients are immunocompromised right immunosuppressed so with that increase in population that is going to be other challenges right so global travel is another one epidemiology is the science of disease transmission there are disease detectives right our health detectives and this is going to include branches of a micro biology ecology statistics sociology and psychology so let's go ahead and let's go over a little bit of history on epidemiology beginning with Jon Snow he's considered to be the father of Epidemiology because he gathered information about victims and interviewed the survivors so what he did is he noticed that individuals in London certain populations of individuals in London were dying from from cholera cholera's terrible infection that we'll talk about later and so what he did is he actually outlined a map and he put little XS where he found that people were becoming the infected and it's interesting because he noticed a pattern and he noticed that the people that were mostly infected were gathered in certain areas that were getting their water from a certain pump so he had this genius idea well what if we clamp that water pump and they don't get it there anymore and they have to go to other places to get their water and boom he solved the problem he solved the problem just like that and so now we may think well that's easy but back then the thought of actually mapping things out was unheard of okay so he gathered information about his victims he laid out his map he interviewed the survivors and he realized that all those individuals were getting their water from that pump there was a brewery nearby and hardly anybody there was getting infected because they were drinking beer interesting right okay let's move on other historical figures in epidemiology inna Semmelweis was a Hungarian physician he's now referred to as the savior of mothers but boy did he take a beating for this hmm how so he had this crazy idea that hand-washing with chlorinated lime solution would decrease the mortality of these women giving birth from 35% and upwards of that to about 1% well of course people thought they were crazy that he was crazy rather yeah they took it personal he just noticed that you know physicians were not washing their hands between you know helping these women delivering these babies and these women's work with these women were developing fevers and dying so he thought what if we hand wash what did we wash our hands with a chlorinated lime solution maybe that's the reason that these women are dying maybe we're infecting them or something - the sort well his hypotheses was seen as very extreme and it was rejected the way that they that they that the other physicians would explain the increased mortality in these women was they attributed the disease to other or different unrelated causes he had a difficulty finding work because of his wild views so what he did is he began to write increasingly angry letters to prominent European obstetricians he went as far as calling them irresponsible murderers everybody was worried about him even his wife was worried about him that he maybe was really losing his mind because nobody believed him they thought he was extreme so in 1865 they actually committed him to an asylum fourteen days later he died and then those European obstetricians thought well why don't we give this hand-washing with chlorinated lime solution as shot and look at that now they even made its own stamp now he's considered the father of anti septic procedures but it costs him his life right and they indeed indeed did see a decrease in mortality rate of these women just crazy just crazy stuff Florence Nightingale mid 18 1918 50s in England she's credited to revolutionising nursing as we know it today she documented typhus the typhus epidemic compiled statistics demonstrating that disease and poor food and unsanitary and sanitary conditions were killing the soldiers so she was a real pioneer for Nursing and patient care so what do our epidemiologists study there are different types of study descriptive analytical experimental in case reporting we're just gonna go quickly through these and just understand what they basically describe or identify beginning what descriptive epidemiology they're going to these describe the occurrences of disease which may be retrospective referring or directed to the past contemplative or past situations it also describes the occurrences of disease that may be prospective or in the future potential likely or expected okay so you just need to basically get an idea of descriptive epidemiology describes rest with retrospective versus prospective its going to essentially identify people at risk based on their location and time of occurrence analytical epidemiologists analyzes disease trends and outbreaks experimental epidemiology will test a hypothesis so they're gonna evaluate the effectiveness of drugs and they usually have a cohort where they have a experimental group that which is the treatment group and in the placebo group I know you'd hate to be the part of the placebo group right but that's important too and then we have case reporting case reporting is going to be basically reporting specific cases of disease outbreak and there are some diseases that are notifiable diseases right now we know that coronavirus is most likely consider notifiable disease because it needs to be reported but there are other sexually transmitted diseases for example that are notifiable diseases tuberculosis aids of course things like that so what do a premie ologists tract they track morbidity versus mortality morbidity refers to the incidence of a specific disease morbidity is the incidence of specific disease whereas mortality is the number of deaths that result from those diseases okay the number of deaths the result from those diseases and we've already outlined incidence vs. prevalence incidence being the number of new cases of disease during a given time usually about a year and this is expressed as a proportional rate and the prevalence is going to involve all those affected regardless of the date of contraption so that's going to be old and new cases and to conclude if you have any questions about infectious disease surveillance I have information for you that you can look at the county level the state the national level and the world level okay and this concludes today's lecture you