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