Presentation on theme: "Microbe-Human Interactions: Contact, Infection and Disease"— Presentation transcript:
1 Microbe-Human Interactions: Contact, Infection and Disease
2 Host-Microbe Relationships: Symbiosis Any organism that harbors another organism or particle (virus, prion)Symbiosis- An association between 2 species (“living together”)MutualismBoth members benefit from relationshipE. coli produce useful products (Vit K) in our large intestineParasitismOne member benefits, one member is harmedCommensalismOne member benefits, one member is not benefited nor harmedMicrobes on our skin utilize skin productsE. Coli in Lg. intestinesGiardia in intestinesDemodex folliculorum in hair follicle
3 Microflora Resident Microflora Transient Microflora Microbes always present on or in the bodyTransient MicrofloraMicrobes present for shorter periods of time (minutes to months)Adult human body consists of:10 trillion (10 13) eukaryotic cells-Human cells100 trillion (10 14) prokaryotic cells-Bacteria cellsWe have 10 times as many prokaryotic cells vs. our own cells!!
4 Resident Microflora Which areas harbor microflora? Which body tissues, organs and fluids are usually microbe-free?The Absence of Resident Microflora can have Harmful EffectsCattle Studies:Enlargement of cecumVitamin deficiencyUnderdeveloped immune system
5 Resident Microbial Compete with Possible Pathogens Microbial Antagonism:Normal biota are unlikely to be displaced by incoming microbesLimited number of attachment sitesChemical or physiological environment created by resident biota is hostile to other microbesNormal biota is beneficial, or at worst, commensal to the host in good health with a functioning immune system
6 First Acquiring Resident Microflora Mother’s birth canalMother’s breast milkBottle-feedingPeopleAirSurfacesThe only time that humans are sterile is when they are in the womb (in utero)
7 Areas of the Body that are usually Sterile BloodUrine in the kidneys, ureters, and bladderCerebrospinal fluidSaliva before oral cavitySemen before the urethraCirculatory systemOrgansGlandsLungsSinusesMiddle and inner earBrainInternal eyeMuscles
8 Contact to Disease Contact: Microbes are present Colonization: The presence of bacteria on body surface (skin, mouth, intestines, airway) without causing diseaseInfection (Infestation-larger parasites)Multiplication of microbes (Microbes penetrate host defenses, enter tissue and multiply)DiseaseDisturbance in normal homeostasis1. doesn’t usually leadto 3. and 4.
9 True vs. Opportunistic Pathogen True pathogenCauses disease in healthy individualsAssociated with a specific and recognizable diseaseOpportunistic pathogenCauses disease in immune compromised hostGain access (injury) to sterile regionsVibrio choleraeStaphylococcus aureus
10 Opportunistic Microbes Opportunists usually do not cause disease unless the “opportunity” arises.Conditions that opportunists can flourish:Failure of the host’s normal defensesImmunocompromised populationsIntro of the organism into unusual body sitesE. coli normal in gut but not urinary tractDisturbances in normal microfloraYeast infection after antibiotic use. Why?
11 Pathogens, Pathogenicity and Virulence Pathogen: Disease causing agentPathogenicity: The ability to cause diseaseVirulence: The degree of pathogenicityVirulence of a microbe is determined by its ability toestablish itself in a hostcause damageVirulence factor: any characteristic or structure of the microbe contributes to its ability to establish itself in the host and cause damage
12 The Progress of an Infection Pathogen needs to become established by being successful at the following:Portals of entryAttachmentSurviving host defensesCausing diseasePortals of exitIf you stop a pathogen from being able to do any of these steps they will not be able to infect the host
13 The Progress of an Infection: 1. Portal of EntryPortal of entry: the route that a microbe takes to enter the tissues of the body to initiate an infectionExogenous: microbe originating from a source outside the body from the environment or another person or animalEndogenous: microbe already existing on or in the body from normal biota or a previously silent infection
14 The Progress of an Infection: 1. Portals of Entry The majority of pathogens have adapted to a specific portal of entryUsually if pathogens enter the “wrong” portal, they will not be infectiousInoculation of the nasal mucosa with the influenza virus will result in infection, but if the virus contacts the skin, no infection occurs
15 The Progress of an Infection: 1. Portals of Entry Occasionally, an infectious agent can enter by more than one portalMycobacterium tuberculosis can enter through both the respiratory and gastrointestinal tractsStreptococcus and Staphylococcus can enter through the skin, urogenital tract, and the respiratory tract
16 The Progress of an Infection: 1. Portals of Entry Infectious dose (ID)The minimum number of microbes necessary to cause an infection to proceedMicroorganisms with smaller infectious doses have greater virulenceID for rickettsia is a single cellID for tuberculosis and beaver fever is about 10 cellsID for gonorrhea is 1,000 cellsID for typhoid fever is 10,000 cellsID for cholera is 1,000,000,000 cells
17 The Progress of an Infection: 2. Attachment/AdhesionGain a stable foothold on host tissuesDependent on binding between specific molecules on both the host and pathogenPathogen is limited to only those cells (and organisms) to which it can bindFirm attachment is almost always a prerequisite for causing disease since the body has so many mechanisms for flushing microbes from tissues
18 The Progress of an Infection: 2. Attachment/AdhesionStructuresCapsulesPili or fimbriaeHooksSpikes
19 The Progress of an Infection: 3. Surviving Host Defenses Microbes not established as normal biota will likely encounter the host immune defenses when first enteringPhagocytes: cells that engulf and destroy host pathogens by means of enzymes and antimicrobial chemicalsWBC engulfing S. cerevisiae
20 The Progress of an Infection: 3. Surviving Host Defenses Antiphagocytic factors:Virulence factors that help pathogens avoid phagocytesLeukocidins: kill phagocytes; Streptococcus and StaphylococcusSlime or capsule: makes it difficult for the phagocyte to engulf the pathogen; Streptococcus pneumoniae and Salmonella typhiSome bacteria survive inside the phagocyte; Legionella, Mycobacterium
21 The Progress of an Infection: 4. Causing DiseaseVirulence factors are adaptations a microbe uses to establish itself in a hostThree ways that microorganisms cause damage to their hostdirectly through the action of enzymesdirectly through the action of toxins (both endotoxins and exotoxins)indirectly by inducing the host’s defenses to respond excessively or inappropriately
22 The Progress of an Infection: 4. Causing Disease-Enzymes Exoenzymesenzymes secreted by microbes that break down and inflict damage on tissuesOften dissolve the host’s defense barriers to promote the spread of disease to other tissuesExamples of exoenzymeshyaluronidase: digests the ground substance that cements animal cells togethercoagulase: causes clotting of blood or plasma
23 The Progress of an Infection: 4. Causing Disease-Exoenzymes
24 The Progress of an Infection: 4. Causing Disease-Toxins Toxin: a specific chemical product of microbes, plants, and some animals that causes cellular damage in other organismsToxins are named according to their targetneurotoxins act on the nervous systementerotoxins act on the intestineshemotoxins lyse red blood cellsnephrotoxins damage the kidneysTwo types of toxins in pathogenic bacteriaExotoxinEndotoxin
25 The Progress of an Infection: 4. Causing Disease-Exotoxins proteins that targets a specific cell typeaffect cells by damaging the cell membrane and initiating lysisDon’t confuse with exoenzymes!Ex: Hemolysinsdisrupt the membrane of red blood cells to release hemoglobinEx. Streptococcus pyogenes and Staphylococcus aureus
26 The Progress of an Infection: 4. Causing Disease-Endotoxins lipopolysaccharide (LPS), part of the outer membrane of gram-negative cell wallsReleased when cells diehas a variety of systemic effects on tissues and organscauses fever, inflammation, hemorrhage, and diarrhea
27 Some endotoxins are pyrogenic The Progress of an Infection:4. Causing Disease-EndotoxinsSome endotoxins are pyrogenic
28 The Progress of an Infection: 5. Portal of ExitEnables pathogen to spread to other hostsRespiratorySalivarySkinFecalUrogenitalBlood
29 The Progress of an Infection: 5. Portal of Exitspecific avenue by which pathogens exitshed through secretion, excretion, discharge, or sloughed tissuehigh number of microbes in these materials increases the likelihood that the pathogen will reach other hostsportal of exit is usually the same as the portal of entry, but some pathogens use a different route
30 Pathogenicity: The ability to cause disease Depends on a pathogen’s ability to:EnterAttachSurvive host defensesCause diseaseExitLook familiar?
31 Virulence: The degree of pathogenicity Intensity of disease producedVirulence can be decreased as a pathogen is sub-cultured time after timeMany virulence factors (weapons) exist to increase a pathogen’s ability to:EnterAttachSurvive host defensesCause diseaseExit
32 Establishment of Infections Localized infection: An infection that is limited to a specific part of the body and has local symptomsSystemic infection: pathogen is distributed throughout the body
33 Establishment of Infections Focal infection: A bacterial infection localized in a specific part of the body, that spreads to other parts of the bodyMixed infection: Bacterial infection composed of different species of bacteria
34 Establishment of Infections Primary and secondary infections: Illness caused by new microbe becoming established in the wake of an initial (primary) infectionAcute: rapid onset of infection, short course of infectionChronic: Long duration of infectionAsymptomatic or subclinical: Not noticed by host
35 Signs, Symptoms and Syndromes Objective/measurable (I.e., fever, inflammation)SymptomsSubjective (pain, tummy ache)SyndromesCombo of signs and symptoms that occur togetherHow would you classify a sore throat? A red throat? A fever?
38 The Persistence of Microbes and Pathologic Conditions Recovery of the host does not always mean the microbe has been removed or destroyed by host defensesLatency: a dormant state of microbes in certain chronic infectious diseasesviral latency: herpes simplex, herpes zoster, hepatitis B, AIDS, Epstein-Barrbacterial/protozoan latency: syphilis, typhoid fever, tuberculosis, malariaSequelae: long-term or permanent damage to tissues or organs caused by infectious diseasemeningitis: deafnessstrep throat: rheumatic heart diseaseLyme disease: arthritispolio: paralysis
39 EpidemiologyEpidemiology: The study of disease within populations (human, plant, etc.)Epidemiology helps us investigate the factors regarding a specific disease:what causes a diseasehow is it transmittedhow do we prevent and treat ithow many people are afflicted.
40 EpidemiologyEpidemiology allows us to take all we have learned about microbes and the diseases they cause and apply that knowledge to new situations.Involves many disciplines: microbiology, anatomy, physiology, immunology, medicine, psychology, sociology, ecology, and statistics
41 Epidemiology Terminology Epidemiologists“disease detectives”, scientists who study epidemiologyEtiologic agentThe cause of a diseaseMorbidityIllnessMortalityDeath
42 Epidemiology Terminology IncidenceNumber of NEW cases within a period of timePrevalenceTOTAL number of cases within a period of timeWhich one informs us if we have taken proper measures to halt disease transmission?
43 Epidemiology Terminology Tracking Disease in the PopulationReportable or notifiable diseasescertain diseases must be reported to authoritiesother diseases are reported on a voluntary basisA network of agencies at the local, district, state, national, and international levels keeps track of infectious diseases
44 Commonly reported diseases that are tracked in the United States
45 Epidemiology Terminology EndemicPathogen is continually present in populationSporadicoccasional cases are reported at irregular intervals at random localesEpidemicAn “outbreak” or higher than normal number of cases. Ie. prevalence of an endemic or sporadic disease is increasing beyond what is expected for a populationPandemicSpread of an epidemic across continents
47 Diphtheria cases after the break up of the former Soviet Union. Is this disease endemic, epidemic, pandemic or sporadic?
48 Statistical data can be represented graphically, and can be used to predict trends We can analyze the data according to year, ages affected, and geographic location to help us predict what diseases we need to watch out for and identify precautions to prevent them. (similar to Influenza H5N1)
49 Epidemiologic Studies Epidemiologists collect data on diseases to help prevent outbreaks in the future.Three Types of Epidemiologic Studies:DescriptiveAnalyticalExperimental
50 Examples of Data from Descriptive Studies Concerned with the physical aspects of an existing disease and disease spread.Provides the what, who, when and whereRecords as many details as possible:Number of casesPopulations affectedLocations and timeAge, gender, race, socioeconomic status, etc.
51 First formal epidemiologic study performed by John Snow in 1854 First formal epidemiologic study performed by John Snow in He traced the source of a cholera epidemic to a certain water pump and proved that people became infected by fecally contaminated drinking water.
52 Analytical StudiesProvides the why and howStudies determine causes and factors that influence the rate of disease. These factors include demographic, biological, behavioral, and environmental influences.Disease groups are compared to control groups and data is analyzed for similarities and differences.Example analytical question: in the hanta virus epidemic, did people get sick if they had been outside near mice habitats or if they had been cooped up in office buildings?
53 Experimental Studies Designs experiments to test a hypothesis. These are the “cleanest” types of studies and often considered the gold-standard.Many experimental studies are performed for pharmaceutical (“clinical trials”) or other treatments.
54 Disease Transmission Disease transmission is affected by: Reservoirs of infectionPortals of Entry and ExitMechanisms of TransmissionWe will investigate all three in order to understand how to break the chain of disease transmission. You can break it at just one site to stop transmission.
55 Disease Transmission: Source of Infection ReservoirThe natural host or habitat (living or nonliving) of a pathogenSourceThe person or item from which an infection is DIRECTLY acquiredCarrier vs. Asymptomatic CarrierAn organism that harbors infections and can spread them to others. They may show symptoms or not.
56 Disease Transmission: Source of Infection Biological vectorAn organism which not only transports a pathogen but also plays a role in the life cycle of the pathogen (virus inside of mosquito, bacteria inside of tick)Mechanical vectorAn organism which only transports a pathogen (fly)
57 Disease Transmission: Source of Infection ZoonosisAn infectious disease humans can acquire from animals (Ex. rabies)70% of all new emerging diseases worldwideimpossible to eradicate without also eradicating the animal reservoirattempts have been made to eradicate mosquitoes and certain rodents
58 Zoonotic infections are caused by vectors and animal reservoirs spreading their own infections to humans
59 Disease Transmission: Source of Infection Human ReservoirsAsymptomatic CarrierSymptomatic CarriersAnimal ReservoirsWild animals (Rabies)Deer mice (hanta virus)InsectsNonliving ReservoirsSoil (Clostridium tetani, Bacillus anthracis)Water (Cholera, Giardia)Food (E. coli, Salmonella, Listeria)
60 Disease Transmission: Source of Infection Some diseases are communicable but others are notCommunicableInfected host transmits an infectious agent to another hostReceiving host must become infectedNon-communicableHost acquires infectious agent but can’t transmit it to anotherFrom self (compromised individual)- microfloraNonliving reservoir – soil-(tetanus)
61 Disease Transmission: Source of Infection CommunicableDisease spread from one host to anotherI.e., cold, meningitisContagiousEasily communicableI.e. measles, influenzaAre all communicable diseases contagious?Are all contagious disease communicable?
62 Disease Transmission: Patterns of Transmission Horizontal transmissionDisease is spread through a population from one infected person to anotherKissing, sneezingVertical transmissionThe disease is transmitted from parent to offspringOvum, sperm, placenta, milk
63 Disease Transmission: Patterns of Transmission Direct (contact)Kissing, sexDroplets (sneezing, coughing directly upon a person within 3 feet)VerticalVectorIndirectContaminated materialsVehicles=Food, water, biological products (blood, serum, tissue), fomite (door knobs, toilet seats, etc.)Fecal-oral (aka oral-fecal)Air (greater than 3 feet away)Droplet nuclei (dried microscopic residue)Aerosols (dust or moisture particles)
64 A sneeze can release enormous amounts of moist droplets, and the dry droplets form droplet nuclei. (so cover your mouth with your elbow )
65 Disease Transmission: Prevention SanitationWhat is the #1 way to stop disease?ImmunizationIsolationQuarantineControl vectorsEducation about prevention and treatment
66 Disease Transmission: Prevention Herd immunity is the proportion of people immune to a certain disease. Is it easier or more difficult to transmit disease when herd immunity is low? How do we acquire herd immunity?
67 Nosocomial Infections: The Hospital as the Source of Disease Nosocomial Infection: An infection acquired in a hospitalAbout 2-4 million (5-20 percent) of admitted patients acquire a nosocomial infection90, 000 die of nosocomial infections$5-10 billion per year to treat nosocomial infections
68 Nosocomial Infections: Contributing Factors compromised patientscollection point for pathogenslowered defenses permit normal biota to enter the bodyinfections acquired directly or indirectly from fomites, medical equipment, other patients, medical personnel, visitors, air, and water
71 Nosocomial Infections Healthcare processes that lead to nosocomial infections:treatments using reusable instruments such as respirators and thermometersindwelling devices such as catheters, prosthetic heart valves, grafts, drainage tubes, and tracheostomy tubes form ready portals of entryhigh proportion of the hospital population receives antimicrobial therapy, drug-resistant microbes are selected for at a much higher rate
72 Nosocomial Infections: Prevention and Control Recent evidence suggests that more than 1/3 of nosocomial infections could be avoided by consistent and rigorous infection control methodsUse Universal Precautions (aka Standard Precautions)Assume all patients and fomites may harbor pathogens