this is part 3 of chapter 14 disease and epidemiology for this part of the chapter we're going to start into the study of epidemiology which is the study of how disease moves in a population and for this part of the chapter I want to look at this as a story of disease from the microbes point of view so for the microbe the microbe has to come from somewhere there is a source of the microbe then that Micro has to be transmitted to the individual who is going to become ill once the microbe gets to that individual it has to enter that individuals body and then of course it will cause disease and at the end the microbe will leave the body so this is what I'm going to be talking about for this lecture going over in general where microbes come from how they get transmitted to an individual how they enter that individuals body and how they leave the body later on in other chapters we'll talk about what actually happens inside the person's body to generate disease this story begins with the source of the microbes and the source of where the microbes come from these are called reservoirs so the basic definition for a reservoir is a continual source of the microbe and one way to think about this is that the reservoir is the natural habitat of the microbe it's where you can always find the microbe it's where the microbe can replicate and get nutrients the first general group of reservoirs are nonliving reservoirs and again think about the reservoir as the natural habitat for the microbe the first type of nonliving reservoir is soil and soil is the natural habitat for several different types of paths I've already talked about the fungi so fungi are naturally found in soil they serve as decomposers also all the different species of Clostridium come from the soil so clustering tootanny clustering botulinum and also bacillus anthracis which causes anthrax the second type of nonliving reservoir is water so any of those microbes that are normally found in the water most specifically entamoeba histolytica which causes that travelers diarrhea so nonliving reservoirs soil and water the second group of reservoirs are the living reservoirs so these are the animals that can Harbor microbes pigs are a very common reservoir as our poultry and I've talked about these before when I talked about ortho my ox of iris which includes the influenza virus influenza has a very broad host range it infects pigs and poultry and humans of course so in areas of the country or areas of the world where pigs and poultry and humans are in close contact you get a lot of inter mixing of the flu virus but this usually happens in poorer areas of Asia this isn't really something we have to worry about in America too much another living risk for common living reservoir are bats so bats hat harbours lots of diseases the most common one you may be aware of is rabies but also Ebola they are considered the reservoir for Ebola and right now they think kovat 19 that coronavirus probably the reservoir is bats but they're not sure just yet bats we don't have to worry about those too much in the United States because we don't come in contact with wild bats all that often so in the United States we don't have to worry about pigs very often we don't have to worry about chickens because we're not living in close contact and bats we don't come in contact with them so what is the living reservoir that we have to worry about the most in the United States that reservoir is children so children are the living reservoirs that we have to be the most worried about in terms of transmitting infectious diseases for two reasons children first of all children under the age of seven their immune systems are not developed yet so whatever microbes they become infected with they Harbor and the second reason is that children are not very hygienic so what they come in contact with a lot of microbes and whatever microbes they come in contact with those microbes are able to replicate in their bodies with the living reservoirs there are basically two types of the animals or humans that we have to be most wary of the first of course are animals humans who are ill if an animal or a human is ill obviously they are infected with a microbe and that microbe is actively replicating in their bodies and they are more likely to transmit it to an individual the other type of living reservoir that transmits a lot of microbes are carriers and I don't know if you've heard about typhoid mary she was a woman who lived in the early 1900s and she worked as a cook for many different families and she was a carrier a carrier of salmonella typhi so she harbored the microbe that caused typhoid but she never became ill with it so when she cooked for her families she was actually transmitting the microbe to them so with the animals the humans we need to be very aware of those that are ill and those that could be potentially be carriers the next part of this sort of disease process disease in a popular is how the microbe moves from the reservoir to the individual who is going to become ill and this is called transmission so going from the reservoir to the individual there are different modes of transmission the first mode of transmission is direct contact direct contact involves touching an individual who harbors the microbe so any kind of direct contact so it could be shaking hands it could be hugging kissing sexual contact or even bites and again this is for any humans or animals so if you come in contact with a human if an animal bites you all of that is direct contact so in this case you have to have physical contact with the individual who harbors the microbe a second type of transmission is in direct contact indirect contact involves the microbe going from a person to an object and then from that object to the person who over get the microbe and become ill and it can be any nonliving object that can transmit the microbe from one person to another person and these objects are called fomites and again any nonliving object can be a foe mite it could be a glass it could be a tissue it could be a doorknob it could be a desk it could be a pen so anything that harbors the microbe for a short period of time another type of transmission is droplet transmission and droplet transmission is referring to the microscopic droplets of water that we release every time we exhale so every time we exhale these microscopic droplets of water are released from our upper respiratory system they are full of microbes so just exhaling releases them talking releases them coughing and of course sneezing sneezing of course you get the most energy the most velocity for all these droplets and those droplets of course are transmitting microbes and especially pathogens if the person is ill now the important thing about droplet transmission is that you need to be within less than a meter one meter of the person to have it be considered droplet transmission so you have to be relatively close to them you don't have to touch them you don't have to touch anything they've touched but just be within one meter of them and you are probably inhaling droplets that they have exhaled next is vehicle transmission now a vehicle is a medium that transmits the microbe from the reservoir to the individual and there are several different types of vehicle transmission the type of vehicle transmission is water so contaminated water can transmit the microbe from the source of contamination to the individual and this is common for cholera Vibe ryuko Larry vibe Ryoka Larry the reservoir is a person and when that person defecates the microbe the bacteria gets into the water and then spreads to another person entamoeba histolytica the water is actually the reservoir so when a person drinks the contaminated water then they acquire the microbe that way ecoli if there's a lot of manure close to the water or human waste sewage then the water can carry the e.coli to infect others and of course ecoli you should know the reservoir is another mammal food is another type of vehicle meat can be contaminated with bacteria from the flora of the animals and this happens during the butchering process chicken is often contaminated with salmonella which is part of the chickens flora as can eggs be contaminated with salmonella beef can be contaminated with e-coli which is part of the cow's normal flora vegetables can be contaminated with microbes from the humans who are working with the vegetables or from the water if the water is contaminated there have been instances where a coli has contaminated the water that was used to water or wash the vegetables and that has caused an e coli food poisoning air is also a vehicle that can carry microbes from one person to another so air and air the microbes are on the air and traveling through the air to another person air sounds very similar to droplet transmission but the difference is that air transmission involves a distance that is greater than one meter so for something to be considered air transmission you can be further than one meter from the person who is releasing the microbe and smallpox is the most famous for having air transmission it is believed that smallpox can travel more than a mile from an infected person to an uninfected person and cause the disease in that recipient the last type of vehicle transmission are bodily fluids and as health care providers these are the ones you're probably going to have to worry about the most so if you have a patient that comes in they're infected with some type of microbe you have to be very aware of their bodily fluids because often the microbe is found in them blood is a very common one as is saliva and diarrhea and vomit so all of those are really common and especially with like Ebola Ebola is the most famous one recently where the vehicle are the different bodily fluids released from the patient's vector transmission is another type of transmission and while technically vector means any living organism that can transmit a microbe usually we use the term vector to indicate insects so for this lecture this chapter any time we use the term vector we are referring to insects with that vector transmission there are two subtypes the first of which is called mechanical transmission and mechanical transmission means that the microbe is on the surface of the insects body and flies are usually the most common type of insect involved in mechanical transmission so flies often are found crawling around on feces on manure on poop and when they do so they pick up the e.coli on their feet so then when the fly when the fly crawls on your food the fly is basically leaving little e coli footprints all over your food so that is mechanical transmission mechanical transmission when the fly or the insect has the microbes on the surface of the body biological transmission is the other type of vector transmission and with biological transmission this means that the inspect is actually infected with the microbe so now the microbe is inside the insects body and when the insect bites the person that then it's injecting the microbe into the person's body so it's different than the mechanical mechanical the micro is just on the surface of the insects body for biological transmission the microbe is inside the insects body the insect is actually infected and then that microbe is injected into the person's body and of course the most common vector for biological transmission is the mosquito lots of different infectious diseases are transmitted by the mosquito there's Plasmodium for malaria there's West Nile virus yellow fever virus Zika is transmitted by mosquitoes also so lots of different diseases are transmitted by mosquitoes there are some other insects that also transmitted via biological transmission these this is an example of a deer tick deer tick is found in this area and that transmits Lyme disease not in this area is a tsetse fly tsetse flies are found in Africa and this transmits Trypanosoma brucei which is for African sleeping sickness related to that is the kissing bug kissing bug is also found in Africa and that transmits tripan Trypanosoma cruzi which causes Chagas disease and then this is kind of famous in history this is a flea and the flea is most known for transmitting your Senia pestis which causes plague so far we've talked about the microbe starting from its reservoir the continual source its habitat and then being transmitted to the individual who's going to be sick so different modes of transmission direct contact and direct contract contact droplet vehicle transmission and vector transmission once it gets to the individual then it has to enter the individual's body and that's called it will use the portal of entry so this is actually how it gets into the person's body the most common portal of entry are the mucous membranes so the mucous membranes are the most common the next portal of entry is the skin and the third portal of entry is called the parenteral route and that involves being injected beneath the skin usually by an insect when talking about the portals entry it's important to know which are the most common portals of entry and of the three types mucous membrane skin and parenteral route the mucous membranes are the most common and if you think about the human body there are different areas where we have mucous membranes so there are different parts of the human body which are much more commonly used as portals of entry the most common portal of entry are the mucous membranes in the respiratory system and this makes sense because we are inhaling all the time and every time we inhale we're drawing in microbes into our body second most common portal of entry are the mucous membranes of the gastrointestinal system and if you think about this we eat several times a day and every time we eat we are taking in water and food which is not sterile so we are bringing microbes into our bodies that way the third most common portal of entry is the urogenital system and this mainly relates to the genital system with sex and of course that's portal of entry for the STDs so these are the three types of mucous membranes respiratory system gastrointestinal system and the urogenital system then the other two portals of entry skin it would be the next common and that's by virtue of the fact that we're covered with skin and our skin comes in contact with objects that harbor the microbes and the least common portal of entry is the blood and that is the parenteral route when microbes are injected into our bodies in to the blood the last part of the story of the microcosm disease in an individual is the portal of exit so the microbe comes from a reservoir it gets transmitted to a person enters through a portal of entry and then the micro wants to leave the person so the microbe needs to infect other hosts in order to propagate itself and again the portals of exit are the same as the portals of entry so mucous membranes with respiratory system is the most common then gastrointestinal then urogenital then you have the skin and the least common would be the parental route with the blood so this part of the lecture was introducing epidemiology basically going through the story of disease in a population from the point of view of the microbe so again the microbe had to come from somewhere so it comes from the reservoir gets transmitted to the individual goes through the portal of entry to get into the person's body and then it will leave the person's body so it can infect other hosts as a review for this part of the lecture what you should do is you should look at your microbes to memorize list and try to figure out for some of the common diseases what would be the reservoir what mode of transmission would be used and what the portal of entry and exit would be in general you can classify diseases into groups so first respiratory diseases common respiratory diseases would be the common cold the flu kovat 19 now measles those are respiratory diseases and in general respiratory diseases the reservoir is another human they can be transmitted by direct contact in direct contact droplet Tran mission and the portal of entry would be the respiratory system which is also the portal of exit usually the portal of entry is the same as the portal of exit gastrointestinal diseases these would be the food poisonings so anything that is transmitted by food so you have ecoli Salmonella contaminated water cholera and two amoeba histolytica so for this you have different types of reservoirs could be the water could be other animals transmission is usually by a vehicle transmission so water or food and the portal of entry is the gastrointestinal system as is the portal of exit again portal of entry is usually the same as the portal of exit sexually transmitted diseases again they tend to have the same method of movement reservoir is another person transmission is direct contact and the portal of entry the same as the puerto vex it is the urogenital system the last general group of diseases are vector borne diseases so this is where the insects are transmitting the diseases again the reservoir is probably the insect the transmission is direct contact because the in the insect has to bite you and then the portal of entry portal of exit is the parenteral route so as a review to practice going through these different modes are these different processes go through your microbes to memorize list and with the common diseases try to determine the reservoir transmission in the portal of entry and exit