Infection, Infectious Diseases, and Epidemiology.
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Transcript of Infection, Infectious Diseases, and Epidemiology.
Infection, Infectious Infection, Infectious Diseases, and EpidemiologyDiseases, and Epidemiology
Symbiosis means “to live together”Symbiosis means “to live together”
Describes the relationship between Describes the relationship between microorganisms and their hostmicroorganisms and their host
3 types3 typesMutualismMutualism
CommenalismCommenalism
ParasitismParasitism
Symbiotic RelationshipsSymbiotic Relationships
The Three Types of Symbiotic The Three Types of Symbiotic RelationshipsRelationships
Also termed normal flora and indigenous microbiotaAlso termed normal flora and indigenous microbiota
Refers to the organisms that colonize the body’s Refers to the organisms that colonize the body’s surfaces without normally causing diseasesurfaces without normally causing disease
Two typesTwo typesResident microbiotaResident microbiota
Transient microbiotaTransient microbiota
Normal MicrobiotaNormal Microbiota
Are a part of the normal microbiota throughout lifeAre a part of the normal microbiota throughout life
Most are commensalMost are commensal
Resident MicrobiotaResident Microbiota
Resident MicrobiotaResident Microbiota
Resident MicrobiotaResident Microbiota
Remain in the body for only hours to months Remain in the body for only hours to months before disappearingbefore disappearing
Found in the same regions as resident microbiotaFound in the same regions as resident microbiota
Cannot persist in the bodyCannot persist in the bodyCompetition from other microorganismsCompetition from other microorganisms
Elimination by the body’s defense cellsElimination by the body’s defense cells
Chemical or physical changes in the body Chemical or physical changes in the body
Transient MicrobiotaTransient Microbiota
Development in the womb is generally free of Development in the womb is generally free of microorganisms (axenic)microorganisms (axenic)
Microbiota begins to develop during the birthing Microbiota begins to develop during the birthing processprocess
Much of one’s resident microbiota established Much of one’s resident microbiota established during the first months of lifeduring the first months of life
Acquisition of Normal MicrobiotaAcquisition of Normal Microbiota
Normal microbiota that can cause disease under certain Normal microbiota that can cause disease under certain circumstancescircumstances
Conditions that provide opportunities for pathogens Conditions that provide opportunities for pathogens
Immune suppressionImmune suppression
Changes in the normal microbiota- changes in Changes in the normal microbiota- changes in relative abundance of normal microbiota may allow relative abundance of normal microbiota may allow opportunity for a member to thrive and cause disease opportunity for a member to thrive and cause disease
Introduction of normal microbiota into unusual Introduction of normal microbiota into unusual site in the bodysite in the body
Opportunistic PathogensOpportunistic Pathogens
Contamination- the mere presence of microbes in or Contamination- the mere presence of microbes in or on the bodyon the body
Infection- results when the organism has evaded the Infection- results when the organism has evaded the body’s external defenses, multiplied, and become body’s external defenses, multiplied, and become established in the bodyestablished in the body
Contamination versus InfectionContamination versus Infection
Sites through which pathogens enter the bodySites through which pathogens enter the body
4 major types4 major types
SkinSkin
Mucous membranesMucous membranes
PlacentaPlacenta
Parenteral routeParenteral route
Portals of EntryPortals of Entry
Outer layer of packed, dead, skin cells usually acts Outer layer of packed, dead, skin cells usually acts as a barrier to pathogensas a barrier to pathogens
Some pathogens can enter through openings or cuts Some pathogens can enter through openings or cuts
Others enter by burrowing into or digesting the Others enter by burrowing into or digesting the outer layers of skinouter layers of skin
SkinSkin
Line the body cavities that are open to the environmentLine the body cavities that are open to the environment
Provides a moist, warm environment that is hospitable Provides a moist, warm environment that is hospitable to pathogens to pathogens
Respiratory tract is the most commonly used site of Respiratory tract is the most commonly used site of entry- entry is through the nose, mouth or eyesentry- entry is through the nose, mouth or eyes
Pathogens able to survive the acidic pH of the stomach Pathogens able to survive the acidic pH of the stomach may use the gastrointestinal tract as a route of entrymay use the gastrointestinal tract as a route of entry
Mucous MembranesMucous Membranes
Some Pathogens that Cross the Some Pathogens that Cross the PlacentaPlacenta
Not a true portal of entry but a means by which Not a true portal of entry but a means by which they can be circumventedthey can be circumvented
Pathogens deposited directly into tissues beneath Pathogens deposited directly into tissues beneath the skin or mucous membranesthe skin or mucous membranes
Parenteral RouteParenteral Route
Process by which microorganisms attach Process by which microorganisms attach themselves to cellsthemselves to cellsRequired to successfully establish colonies Required to successfully establish colonies within the hostwithin the hostUses adhesion factorsUses adhesion factors
Specialized structuresSpecialized structuresAttachment proteinsAttachment proteins
AdhesionAdhesion
Found on viruses (attachment proteins) and Found on viruses (attachment proteins) and many bacteria (adhesins)many bacteria (adhesins)Surface lipoproteins or glycoproteins, called Surface lipoproteins or glycoproteins, called ligands, that bind host cell receptorsligands, that bind host cell receptorsInteraction of ligand with host receptor can Interaction of ligand with host receptor can determine specificity for host cellsdetermine specificity for host cellsAbility to change or block the ligand or its Ability to change or block the ligand or its receptor can prevent infectionreceptor can prevent infectionInability to make attachment proteins or adhesins Inability to make attachment proteins or adhesins renders the microorganisms avirulentrenders the microorganisms avirulent
Attachment ProteinsAttachment Proteins
Infection is the invasion of the host by a pathogenInfection is the invasion of the host by a pathogen
Disease results only if the invading pathogen Disease results only if the invading pathogen alters the normal functions of the bodyalters the normal functions of the body
Disease is also referred to as morbidityDisease is also referred to as morbidity
Infection versus DiseaseInfection versus Disease
Symptoms- subjective characteristics of disease Symptoms- subjective characteristics of disease felt only by the patientfelt only by the patient
Signs- objective manifestations of disease that can Signs- objective manifestations of disease that can be observed or measured by othersbe observed or measured by others
Syndrome- group of symptoms and signs that Syndrome- group of symptoms and signs that characterize a disease or abnormal conditioncharacterize a disease or abnormal condition
Asymptomatic, or subclinical, infections lack Asymptomatic, or subclinical, infections lack symptoms but may still have signs of infection symptoms but may still have signs of infection
Manifestations of DiseaseManifestations of Disease::
Study of the cause of diseaseStudy of the cause of disease
Germ theory of disease- disease caused by Germ theory of disease- disease caused by infections of pathogenic microorganismsinfections of pathogenic microorganisms
Robert Koch developed a set of postulates one Robert Koch developed a set of postulates one must satisfy to prove a particular pathogen causes must satisfy to prove a particular pathogen causes a particular diseasea particular disease
EtiologyEtiology
Figure 14.7
Using Koch’s postulates is not feasible in all casesUsing Koch’s postulates is not feasible in all casesSome pathogens can’t be cultured in the laboratorySome pathogens can’t be cultured in the laboratory
Some diseases are caused by a combination of Some diseases are caused by a combination of pathogens and other cofactorspathogens and other cofactors
Ethical considerations prevent applying Koch’s Ethical considerations prevent applying Koch’s postulates to pathogens that require a human hostpostulates to pathogens that require a human host
Difficulties in satisfying Koch’s postulatesDifficulties in satisfying Koch’s postulatesDiseases that can be caused by more than one pathogenDiseases that can be caused by more than one pathogen
Pathogens that are ignored as potential causes of Pathogens that are ignored as potential causes of diseasedisease
Exceptions to Koch’s PostulatesExceptions to Koch’s Postulates
Pathogenicity- ability of a microorganism to Pathogenicity- ability of a microorganism to cause diseasecause disease
Virulence- degree of pathogenicityVirulence- degree of pathogenicityVirulence factors contribute to an organism’s Virulence factors contribute to an organism’s
virulencevirulenceAdhesion factorsAdhesion factors
Extracellular enzymesExtracellular enzymes
ToxinsToxins
Antiphagocytic factorsAntiphagocytic factors
Virulence Factors of Infectious DiseaseVirulence Factors of Infectious Disease
Enzymes secreted by the pathogenEnzymes secreted by the pathogen
Dissolve structural chemicals in the bodyDissolve structural chemicals in the body
Help pathogen maintain infection, invade Help pathogen maintain infection, invade further, and avoid body defensesfurther, and avoid body defenses
Extracellular EnzymesExtracellular Enzymes
Chemicals produced by the pathogenChemicals produced by the pathogen
Harm tissues or trigger host immune responses Harm tissues or trigger host immune responses that cause damagethat cause damage
Toxemia refers to toxins in the bloodstream that Toxemia refers to toxins in the bloodstream that are carried beyond the site of infectionare carried beyond the site of infection
2 types2 typesExotoxinsExotoxins
EndotoxinsEndotoxins
ToxinsToxins
A Comparison of Bacterial A Comparison of Bacterial Exotoxins and EndotoxinsExotoxins and Endotoxins
Certain factors prevent phagocytosis by the Certain factors prevent phagocytosis by the host’s phagocytic cellshost’s phagocytic cells
Bacterial capsule Bacterial capsule Often composed of chemicals found in the body and not Often composed of chemicals found in the body and not recognized as foreignrecognized as foreign
Can be slippery making it difficult for phagocytes to engulf Can be slippery making it difficult for phagocytes to engulf the bacteriathe bacteria
Antiphagocytic chemicalsAntiphagocytic chemicalsSome prevent fusion of lysosome and phagocytic vesiclesSome prevent fusion of lysosome and phagocytic vesicles
Leukocidins directly destroy phagocytic white blood cellsLeukocidins directly destroy phagocytic white blood cells
Antiphagocytic FactorsAntiphagocytic Factors
Following infection, sequence of events called the Following infection, sequence of events called the disease process occursdisease process occurs
Many infectious diseases have five stages Many infectious diseases have five stages following infectionfollowing infection
The Stages of Infectious DiseaseThe Stages of Infectious Disease
Pathogens leave host through portals of exitPathogens leave host through portals of exitMovement of Pathogen Out of HostMovement of Pathogen Out of Host
Figure 14.11
Most pathogens cannot survive long outside of Most pathogens cannot survive long outside of their hosttheir host
Sites where pathogens are maintained as a source Sites where pathogens are maintained as a source of infection are termed reservoirs of infection of infection are termed reservoirs of infection
3 types of reservoirs3 types of reservoirsAnimal reservoirAnimal reservoir
Human carriersHuman carriers
Nonliving reservoirNonliving reservoir
Reservoirs of InfectionReservoirs of Infection
Zoonoses- diseases that are naturally spread Zoonoses- diseases that are naturally spread from their usual animal host to humansfrom their usual animal host to humans
Acquire zoonoses through various routesAcquire zoonoses through various routesDirect contact with animal or its wasteDirect contact with animal or its waste
Eating animalsEating animals
Bloodsucking arthropodsBloodsucking arthropods
Humans are usually dead end host to zoonotic Humans are usually dead end host to zoonotic pathogenspathogens
Animal ReservoirsAnimal Reservoirs
Infected individuals who are asymptomatic but Infected individuals who are asymptomatic but infective to othersinfective to others
Some individuals will eventually develop illness Some individuals will eventually develop illness while others never get sickwhile others never get sick
Human CarriersHuman Carriers
Soil, water, and food can be reservoirs of infectionSoil, water, and food can be reservoirs of infectionPresence of microorganisms is often due to Presence of microorganisms is often due to
contamination by feces or urinecontamination by feces or urine
Nonliving ReservoirsNonliving Reservoirs
Transmission from either a reservoir or portal of exitTransmission from either a reservoir or portal of exit
3 groups3 groupsContact transmission (Direct, Indirect, droplet)Contact transmission (Direct, Indirect, droplet)
Vehicle transmission (Air-borne, Food-borne, Water-Vehicle transmission (Air-borne, Food-borne, Water-borne)borne)
Vector transmission (Biological, Mechanical)Vector transmission (Biological, Mechanical)
Modes of Infectious Disease TransmissionModes of Infectious Disease Transmission
Modes of Disease TransmissionModes of Disease Transmission
Many different methods of classificationMany different methods of classificationThe body system they affectThe body system they affect
The taxonomic groups of the causative agentThe taxonomic groups of the causative agent
Their longevity and severityTheir longevity and severity
How they are spread to their hostHow they are spread to their host
Classification of Infectious DiseasesClassification of Infectious Diseases
Terms Used to Classify Infectious DiseasesTerms Used to Classify Infectious DiseasesAcute diseaseAcute disease Disease in which symptoms develop rapidly and that runs its Disease in which symptoms develop rapidly and that runs its coursecourse
quickly.quickly.Chronic diseaseChronic disease Disease with usually mild symptoms that develop slowly and Disease with usually mild symptoms that develop slowly and last a last a long time.long time.Subacute diseaseSubacute disease Disease with time course and symptoms between acute and Disease with time course and symptoms between acute and chronic.chronic.
Asymptomatic diseaseAsymptomatic disease Disease without symptoms.Disease without symptoms.
Latent diseaseLatent disease Disease that appears a long time after infection.Disease that appears a long time after infection.
Communicable diseaseCommunicable disease Disease transmitted from one host to another.Disease transmitted from one host to another.
Contagious diseaseContagious disease Communicable disease that is easily spread.Communicable disease that is easily spread.
Noncommunicable diseaseNoncommunicable disease Disease arising from outside of hosts or from opportunistic Disease arising from outside of hosts or from opportunistic pathogen.pathogen.
Local infectionLocal infection Infection confined to a small region of the body.Infection confined to a small region of the body.
Systemic infectionSystemic infection Wide spread infection in many systems of the body; often travels in Wide spread infection in many systems of the body; often travels in the blood or lymph.the blood or lymph.
Focal infectionFocal infection Infection that serves as a source of pathogens for infections at Infection that serves as a source of pathogens for infections at other other sites in the body.sites in the body.Primary infectionPrimary infection Initial infection within a given patient.Initial infection within a given patient.
Secondary infectionSecondary infection Infections that follow a primary infection; often by opportunistic Infections that follow a primary infection; often by opportunistic pathogens.pathogens.
Study of where and when diseases occur and Study of where and when diseases occur and how they are transmitted within populationshow they are transmitted within populations
Track occurrence of diseases using two measuresTrack occurrence of diseases using two measuresIncidence- number of Incidence- number of newnew cases of a disease in a cases of a disease in a
given area during a given period of timegiven area during a given period of time
Prevalence- number of Prevalence- number of total total cases of a disease in a cases of a disease in a given area during a given period of timegiven area during a given period of time
Occurrence also evaluated in terms of frequency Occurrence also evaluated in terms of frequency and geographic distributionand geographic distribution
EpidemiologyEpidemiology
Infections acquired while in a health care facilityInfections acquired while in a health care facility
Types of nosocomial infectionsTypes of nosocomial infectionsExogenous- pathogen acquired from the health care Exogenous- pathogen acquired from the health care
environmentenvironment
Endogenous- pathogen arise from normal microbiota Endogenous- pathogen arise from normal microbiota due to factors within the health care settingdue to factors within the health care setting
Iatrogenic- results from modern medical proceduresIatrogenic- results from modern medical procedures
Nosocomial InfectionsNosocomial Infections
Involves precautions designed to reduce the factors Involves precautions designed to reduce the factors that result in diseasethat result in disease
Universal Precautions instituted by the CDC to Universal Precautions instituted by the CDC to limit exposure to pathogenslimit exposure to pathogens
Hand washing is the most effective way to reduce Hand washing is the most effective way to reduce nosocomial infectionsnosocomial infections
Control of Nosocomial InfectionsControl of Nosocomial Infections