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Week 5 Notes

by: Katlyn Palka

Week 5 Notes HTH 245

Katlyn Palka

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Notes from class and chapter 7 in the textbook
Foundations of Infectious Disease
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This 6 page Class Notes was uploaded by Katlyn Palka on Sunday October 2, 2016. The Class Notes belongs to HTH 245 at James Madison University taught by in Fall 2016. Since its upload, it has received 5 views. For similar materials see Foundations of Infectious Disease in Health Sciences at James Madison University.

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Date Created: 10/02/16
Chapter 7: Concepts of Microbial Disease ● Symbiosis: describes an association between two or more species with three  possibilities:  ○ Mutualism:  ■ Both members of the association enjoy benefits  ■ Ex: the association between termites and  protozoans (pg. 153) ○ Parasitism: ■ An association in which a parasite (microbe) lives  at the expense of the host (the human) ● Parasite: all microbes, worms,  viruses that produce disease  ○ Commensalism:  ■ The relationship between two or more species in  which one benefits and the other is indifferent (neither benefited nor  harmed) ○ These three possibilities aren’t cut and dry, there are blurred lines  and grey areas between the three of them ○ The see­saw relationship between mutualism, commensalism,  and parasitism ■ For mutualism and commensalism when there are  nonpathogens there is balance between the two. The nonpathogens don’t cause any harm ■ For parasitism the non­pathogens that normally  wouldn’t cause any harm become opportunists ● When you already have a depressed immune system the nonpathogens become pathogens which can  cause the risk of disease to become higher ● Example: HIV ● Microbes as agents of disease ○ Miasmas ■ Were thought to be the cause of disease ■ People thought that bad air was the cause of  disease and death ○ In the early 1800s there was a link made between lack of  sanitation and disease ■ This is the beginning of germ theory ● Koch’s postulates (the steps to prove a particular agent causes an illness  based on bacteria) ○ 1. Association ■ The causative agent must be present in every case  of a specific disease ■ Every person that has the disease must test  positive for that agent that you propose is causing the disease ○ 2. Isolation ■ The causative agent must be isolated in every case of the disease and grown in pure culture ■ Take the microbes out of the infected person and  culture them ○ 3. Causation ■ The causative agent in the pure culture must cause the disease when inoculated into a healthy and susceptible laboratory  animal ■ Take the thing you took out of the diseased people  and put it in a healthy species and it should get sick ○ 4. Reisolation ■ The causative agent must be reisolated from the  laboratory animal and be identical to the original causative agent ■ Take it out again and make sure it was the same  microbe you put in the species in the first place ● Microbial mechanisms of disease ○ Infection:  ■ When you have the microbe in you and it’s  multiplying, but you don’t have any symptoms  ● Asymptomatic or subclinical ○ Disease: ■ When you start to show symptoms  ○ The chance of acquiring an infection depends on 3 factors ■ Dose (n) ● The number of microbes that are  encountered ■ Virulence (V) ● Virulence factors ■ Resistance (R) ● Host immunity ■ There is a formula that determines the severity of  an infection and can tell whether or not a person will end up getting a  disease from the infection ● D=nV/R ● D is the severity of the infectious  disease ● Pathogenicity and Virulence ○ There is an infective dose (ID), which is the minimal dose that is  necessary to establish an infection in the host ■ More virulent organisms have a smaller ID than  less virulent organisms ● It takes less microbes to make you  sick (more virulence) ○ It doesn’t need as  many copies of itself to make you sick ○ LD❑ 50is the 50% lethal dose ■ It is a laboratory measurement of virulence that is  determined by injecting animals with varying concentrations of microbes  and the dose that kills 50% of the animals in an established time ○ Pathogenicity: the ability to cause disease ○ Virulence: a measure of pathogenicity ■ Encompasses two types of virulence factors that  enable pathogens to overcome host defense mechanisms and to multiply  and cause damage ● Defensive strategies (4) ○ They allow microbes  to escape destruction by the host immune system ■ Bacter ial adhesins ● A dhere to receptor molecules at port of entry ■ Capsu les, M protein, Waxy cell wall ● I nterferes with phagocytosis, multiplies  inside immune cells ■ Antige nic variation ● C hanges surface antigens to avoid detection  by antibodies ■ Enzym e secretion ● A llows it to survive in harsh environments ● Offensive strategies (3) ○ They result in  damage to the host ■ Exoen zymes ● H elp to spread bacteria by causing damage  to host cells ■ Exoto xins ● P roteins synthesized by the microbe and  secreted into the host’s tissues (only in  gram positive) ■ Endot oxins ● T hey are structural components of outer  membrane of gram negative cells. Called  lipopolysaccharides ● T hey are not usually released during  microbial growth and metabolism ● Virulence mechanisms of viruses ○ Defensive side: ■ Since they are obligate intracellular parasites (they  depend on the their host cells for survival and replication) which allows  them to go through antigenic variation ● They can change their antigen coats which hide from components of the immunes system ● Example: influenza virus ○ Offensive side: ■ Consists of death (lysis) of the host cell from:  ● Production of large numbers of  replicating viruses ● Inhibiting host protein synthesis ● Damage to plasma membrane ● Inhibiting host cell metabolism  ● Stages of microbial disease ○ Incubation ■ The time between the pathogen’s access to the  body and the display of signs and symptoms ● No symptoms are shown in this  stage ● The infected individual is contagious  here  ● This stage can vary in time ○ Staph food poisoning  (2­4 hours) ○ HIV (6 months to 12  years)  ○ Prodromal ■ A short stage ■ The symptoms are vague and mild ● Frequently characterized by  tiredness, headache, muscle aches ■ The infected individual may be contagious  depending on the infection ○ Illness ■ The disease is acute ■ Most severe stage ■ It is accompanied by typical symptoms ● Fever, nausea, vomiting, chills,  headache, muscle pain, fatigue, swollen lymph glands, and rash ■ In this stage either you recover or you die ● Results in either recovery or  impairment or death of the host ○ Decline ■ The immune system won the battle ■ The signs and symptoms start to disappear  ■ You start to feel better ○ Convalescence  ■ This is the recovery stage ■ There is repair of damaged tissues and strength is  regained ■ In some cases a person can become a chronic  carrier ● Sometimes with cholera and typhoid  fever, but this is where the disease stays in you forever, but you  aren’t sick and you show no symptoms  Class Notes 9/28 ● Video: ○ Miasma: bad air (floating in specific regions) ■ They thought it could be treated with good smells in the air (flowers, incense)  ■ The beak would hold the incense and herbs that  could beat miasma  ● Video: how a few scientists transformed the way we think about disease ○ Cholera outbreaks led to the discovery of microbes ■ Spread through infected water ■ He mapped the city and shut down a water pump  ■ Childs dirty diapers were thrown into a waste  section which then contaminated the water ○ Germ theory: microbes were found using early microbes ● Video: Flu vaccine ○ Viruses are always changing  ○ The antibodies become out of date and can’t protect from the  influenza each year  ○ Attach to the Ha protein and block it and prevent it from spreading ○ When the influenza enters cells and when it replicates it can  change a little bit and eventually the immune system can’t recognize the antigens anymore that is why we need a new flu vaccine ○ They predict the type of flu that will circulate each year and that is  the flu vaccine that they create each year  ○ Has a low uptake: low amount of people that get the flu vaccine


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