Symbiotic Relationships Between Microbes and Their Hosts
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Symbiosis means “to live together”We have symbiotic relationships with
countless microorganismsTypes of symbiosis
MutualismCommensalismParasitism
InfectionMutualsim: Each one benefitsCommensual: One organism benefits,
the other is not harmed.Parasitism: Advantage to one,
disadvantage to the other.
Obligate relationship: one depends on the other for survival (parasites are obligate pathogens)
Normal Flora: Organism is always on or in us; GI, GU, oral mucosa.
Sterile areas of the body: Blood, CSF. Any organism here indicates something is wrong. The first indicator is decreased glucose, increased protein
Opportunistic Pathogens: A normal flora organism that becomes a pathogen when the host’s immune defense decreases.
Trauma, Surgery, Burns: overcomes barriers of defense
Catheterization: allows increased access and decreased defense
Chemotherapy: e.g. ablative (for CA) destroys bone marrow,
therefore myeloid and lymphoid immunity goes down.
Co-infection: e.g. haemophilic influenza is 2° to viral influenza.
Tissue TropismTissue Tropism (organisms are selective of
tissues they infect): influenza does not affect your hand; gonorrhea only effects mucosa. Tropism can also be species, organ, or non-specific.
HIV integrates a provirus into our chromosome. Antibodies actually assist the HIV organisms because opsinization helps to internalize the virus. Because of almost no cell mediated immunity (T-cells are infected), AIDS patients die from TB, cytomegalovirus (CMV), Candida, pneumocystis. When a person has a second infection, it is called a CO-INFECTION.
OBLIGATE PATHOGENSWill always cause infection and
disease whenever and wherever they are encountered (e.g. Yersinia pestis plague, anthrax, smallpox) unless you are immune. However, they don’t want to kill their host.
Virulence VIRULENCE: Ability to cause infection and disease. MULTIPLICITY OF INFECTION (INNOCULUM): the number of
organisms needed to cause disease. There is an inverse relationship
between virulence and Multiplicity of Infection. If only a few bacterial
cells cause the disease, it is said to be very virulent.
Obligate pathogens are virulent, even with a low inoculum, because
they are effective. Most innoculum needs 103-5 organisms. Only 10
organisms can form an innoculum in a virulent organism such as
anthrax.
Anthrax avoids immune defenses by exploiting the very mechanisms
used to fight it. It becomes activated after phagocytosis. Mycobacterium will coat the wall of vacuoles so lysozymes can’t fuse. Rickettsia is on a timer, and escapes the vacuole to invade the
nucleus.
PORTALS OF ENTRY (POE)CEPHALIC (7 PORTALS): Mouth, nose,
eyes, ears.CORPOREAL: Mammary, Vaginal,
Urethral, RectalTRAUMA/MEDICAL: Burn, Compound
Fracture, surgical/catheter, injury/IVDA, abnormal mucosa (CA chemo).
MODES OF TRANSMISSION (MOT)
AEROSOL: Airborne micro-particles (soil aerosol containing endospores)
DROPLET NUCLEI: Mucoid micro-droplet via cough or sneeze, durable on surfaces, mainly transmitted by contact. Sneeze and cough into your elbow!
DIRECT CONTACT: Direct object/tissue-to-tissue contact.o CASUAL TRANSMISSION: handshake, clothingo ASPIRATION: inhalation of oral, GI, or food-borne
organismso FECAL-ORAL: autoinoculation or contamination (poor hygiene)o SEXUAL TRANSMISSION (STD): sexual/bodily fluid
contact
AGENTS OF TRANSMISSIONVECTOR: a living organism that spreads
disease from one host to another. (mosquitoes, ticks, rats, humans)FOMITE: inanimate object that spreads
disease from one host to another. (toothbrush, water glass, toys, handles)
HOST-PATHOGEN RELATIONSHIP (HPR)
INFECTION: presence of organism DISEASE: adverse symptoms due to infection NORMAL FLORA: organism typically found on healthy individual PATHOGEN: organism causing disease (etiologic agent) IMMUNOCOMPROMISED: suppressed or deficient immunity NOSOCOMIAL: acquired in hospital setting COMMUNITY-ACQUIRED: acquired in routine, day-to-day activities OPPORTUNISTIC PATHOGEN: normal flora + compromised pathogen OBLIGATE PATHOGEN: always causes Dz if present PATHOGENESIS (Px): events leading to Dz (POEDz) MULTIPLICITY OF INFECTION (MOI): inoculum required for infxn INCUBATION (INC): time from transmission to Dz VIRULENCE: measure of Dz capability VIRULENCE FACTOR (VF): ultrastructure, exoenzyme, or exotoxin
BACTERIAL SYMPTOM TERMINOLOGY
BACTEREMIA: bacteria in bloodstream BACTERURIA: bacteria in urine (normal or pathogenic flora) SEPTICEMIA: Gram negative bacteremia in the bloodstream PYEMIA: Gram + bacteremia PYROGENIC: fever-producing infection or bacterial components PURULENT: pus-producing, reaches an opening to drain out. The pus is a
collection of dead neutrophils, which are the 1° immune cells when there is pus. GRANULOMATOUS: infxn where macrophages are 1° immune cells (no pus) DIFFERENTIAL DIAGNOSIS (DDx): all possible causes of the disease. UROSEPSIS: Septicemia from UTI FACULTATIVE INTRACELLULAR PARASITES: are not obligate pathogens.
They can survive temporarily in white cells, such as neutrophils, Monocytes/ Macrophages.
EXOTOXINS: A toxin made and then secreted, e.g. pesticin, hemolysins, shigatoxins, choleragen, enterotoxins, plasminogen activating factor, coagulase, etc.
ENDOTOXINS: A component of the cell wall is toxic to us, e.g. LPS and LOS.
Symbiotic Relationships Between Microbes and Their Hosts
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Normal Microbiota in HostsAlso termed normal flora and indigenous microbiota
Organisms that colonize the body’s surfaces without normally causing disease
Two typesResident microbiotaTransient microbiota
Symbiotic Relationships Between Microbes and Their Hosts
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Resident microbiotaAre a part of the normal microbiota
throughout lifeAre mostly commensal
Transient microbiotaRemain in the body for short periodFound in the same regions as resident
microbiotaCannot persist in the body
Competition from other microorganismsElimination by the body’s defense cellsChemical or physical changes in the body
Symbiotic Relationships Between Microbes and Their Hosts
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Acquisition of normal microbiotaDevelopment in womb free of
microorganisms (axenic)Microbiota begin to develop during
birthing processMuch of one’s resident microbiota
established during first months of life
Symbiotic Relationships Between Microbes and Their Hosts
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How Normal Microbiota Become Opportunistic PathogensOpportunistic pathogens
Normal microbiota that cause disease under certain circumstances
Conditions that provide opportunities for pathogensIntroduction of normal microbiota into
unusual site in bodyImmune suppressionChanges in the normal microbiota
Changes in relative abundance may allow opportunity for a member to thrive and cause disease
Cell surface markers
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Designated as “CD”Cluster of Differentiationused to identify specific structures on a cell
~200 different designations
Reservoirs of Infectious Diseases of Humans
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Most pathogens cannot survive for long outside of their host
Reservoirs of infectionSites where pathogens are maintained as a source of infection
Three types of reservoirsAnimal reservoirHuman carriersNonliving reservoir
Reservoirs of Infectious Diseases of Humans
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Animal ReservoirsZoonoses
Diseases naturally spread from animal host to humans
Acquire zoonoses through various routesDirect contact with animal or its waste
Eating animalsBloodsucking arthropods
Humans are usually dead-end host to zoonotic pathogens
Reservoirs of Infectious Diseases of Humans
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Human CarriersInfected individuals who are asymptomatic but infective to others
Some individuals eventually develop illness while others never get sick
Healthy carriers may have defensive systems that protect them
Reservoirs of Infectious Diseases of Humans
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Nonliving Reservoirs Soil, water, and food can be reservoirs of infectionPresence of microorganisms often due to contamination by feces or urine
The Movement of Microbes into Hosts: Infection
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Exposure to Microbes: Contamination and Infection Contamination
The mere presence of microbes in or on the body
Infection When organism evades body’s external defenses, multiplies, and becomes established in the body
The Movement of Microbes into Hosts: Infection
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Portals of Entry Sites through which pathogens enter the body
Four major pathwaysSkinMucous membranesPlacentaParenteral route (intravenous)
The Movement of Microbes into Hosts: Infection
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Portals of Entry Skin
Outer layer of dead skin cells acts as a barrier to pathogens
Some pathogens can enter through openings or cuts
Others enter by burrowing into or digesting outer layers of skin
The Movement of Microbes into Hosts: Infection
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Portals of Entry Mucous membranes
Line the body cavities that are open to the environment
Provide a moist, warm environment hospitable to pathogens
Respiratory tract is the most common site of entry Entry is through the nose, mouth, or eyes
Gastrointestinal tract may be route of entryMust survive the acidic pH of the stomach
The Movement of Microbes into Hosts: Infection
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Portals of Entry Placenta
Typically forms effective barrier to pathogens
Pathogens may cross the placenta and infect the fetusCan cause spontaneous abortion, birth defects, premature birth
The Movement of Microbes into Hosts: Infection
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Portals of Entry Parenteral route
Not a true portal of entryPathogens deposited directly into tissues beneath the skin or mucous membranes (needle injection or i.v.)
The Movement of Microbes into Hosts: Infection
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The Role of Adhesion in Infection Process by which microorganisms attach themselves to cells
Required to successfully establish colonies within the host
Adhesion factors includeSpecialized structures (acts like Velcro)Attachment proteins (acts like glue)The presence of adhesions are considered a virulence factor.
The Movement of Microbes into Hosts: Infection
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The Role of Adhesion in Infection Attachment proteins help in adhesion
Found on viruses and many bacteriaViral or bacterial ligands (proteins) bind host cell receptorsInteraction can determine host cell specificity
Changing/blocking a ligand or its receptor can prevent infection
Inability to make attachment proteins or adhesins renders microorganisms avirulent
Some bacterial pathogens attach to each other to form a biofilm
The Nature of Infectious Disease
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Infection is the invasion of the host by a pathogen
Disease results if the invading pathogen alters normal body functions
Disease is also referred to as morbidity
The Nature of Infectious Disease
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Manifestations of Disease: Symptoms, Signs, and SyndromesSymptoms
Subjective characteristics of disease felt only by the patient
Signs Objective manifestations of disease
observed or measured by othersSyndrome
Symptoms and signs that characterize a disease or abnormal condition
Asymptomatic, or subclinical, infections lack symptoms but may still have signs of infection
The Nature of Infectious Disease
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Cause of Disease: EtiologyStudy of the cause of diseaseGerm theory of disease
Disease caused by infections of pathogenic microorganisms
Robert Koch developed a set of postulates one must satisfy to prove a particular pathogen causes a particular disease
The Nature of Infectious Disease
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Causation of Disease: EtiologyExceptions to Koch’s postulates
Some pathogens can’t be cultured in the laboratoryDiseases caused by a combination of pathogens
and other cofactorsEthical considerations prevent applying Koch’s
postulates to pathogens that require a human hostDifficulties in satisfying Koch’s postulates
Diseases can be caused by more than one pathogen
Pathogens that are ignored as potential causes of disease
The Nature of Infectious Disease
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Virulence Factors of Infectious AgentsPathogenicity
Ability of a microorganism to cause disease
VirulenceDegree of pathogenicity (how good is it at
its job?)Virulence factors contribute to virulence
Adhesion factorsBiofilmsExtracellular enzymesToxinsAntiphagocytic factors
The Nature of Infectious Disease
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Virulence Factors of Infectious AgentsExtracellular enzymes
Secreted by the pathogenDissolve structural chemicals in the body
Help pathogen maintain infection, invade, and avoid body defenses
The Nature of Infectious Disease
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Virulence Factors of Infectious AgentsToxins
Chemicals that harm tissues or trigger host immune responses that cause damage
Toxemia refers to toxins in the bloodstream that are carried beyond the site of infection
Two typesExotoxins (made and secreted)Endotoxins (part of the bacterial cell wall)
The Nature of Infectious Disease
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Virulence Factors of Infectious AgentsAntiphagocytic factors
Factors prevent phagocytosis by the host’s phagocytic cellsBacterial capsule
oComposed of chemicals not recognized as foreign
oSlippery; difficult for phagocytes to engulf bacteria
Antiphagocytic chemicalsoPrevent fusion of lysosome and phagocytic
vesiclesoLeukocidins directly destroy phagocytic white
blood cells
The Nature of Infectious Disease
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The Stages of Infectious DiseaseThe disease process occurs following infection
Many infectious diseases have five stages following infectionIncubation periodProdromal periodIllnessDeclineConvalescence
The Movement of Pathogens Out of Hosts: Portals of Exit
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Pathogens leave host through portals of exit
Many portals of exit are the same as portals of entry
Pathogens often leave hosts in materials the body secretes or excretes
Modes of Infectious Disease Transmission
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Transmission is from a reservoir or a portal of exit to another host’s portal of entry
Three groups of transmissionContact transmission
Direct, indirect, or dropletVehicle transmission
Airborne, waterborne, or foodborneVector transmission
Biological or mechanical
Classification of Infectious Diseases
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Diseases can be classified in number of waysThe body system they affect
GI system, nervous system, bloodTaxonomic categories
Viral disease, Gram +Their longevity and severity
Chronic vs. acute; mild vs. severeHow they are spread to their host
STD, blood borne, foodThe effects they have on populations (rather than on individuals): global/pandemic vs. epidemic
Classification of Infectious Diseases
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Terms used to classify infectious diseaseAcute disease (rapid onset, short duration)
Chronic disease (long duration)Subacute disease (slower onset, medium duration)
Latent disease (present but not obvious system)
Communicable (Contagious)
Epidemiology of Infectious Diseases
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INFECTION: Presence of microbeDISEASE: Symptomatic consequence of infection
EpidemiologyEpidemiology is the study of the patterns,
causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health by identifying risk factors for disease and provides information for preventive healthcare.
Major areas of epidemiological study include disease etiology, outbreak investigation, disease surveillance and screening, biomonitoring, and comparisons of treatment effects such as in clinical trials.
John Snow Dr. John Snow is
known as the father of modern epidemiology. He showed that cholera was water-borne, and debunked the Miasma theory, which stated that cholera came from bad air.
John Snow John Snow was a British physician in London in
1854, where a major cholera outbreak struck the nearby city of Soho.
In three days, 127 people who lived near Broad Street died of Cholera. Within a week, 500 people had died and one in seven people who developed cholera eventually died from it.
John Snow suspected contamination of the water, but couldn’t find any organic matter in it. Almost all the cases of cholera occurred close to the Broad Street Water Pump.
Snow mapped out the cases of cholera in relation to the water pump.
The evidence Snow presented convinced the local council to remove the pump handle, halting the spread of the disease. It wasn’t until 1885, when Robert Koch identified V. cholerae as the bacillus causing the disease that he had proof of his theory. He was right, but wasn’t around to see this discovery himself. John Snow died four years later, at the age of 45.
Epidemiology of Infectious Diseases
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Frequency of DiseaseTrack occurrence of diseases using two measuresIncidence
Number of new cases of a disease in a given area during a given period of time
Prevalence Number of total cases of a disease in a given area during a given period of time
Occurrence also evaluated in terms of frequency and geographic distribution
Epidemiology of Infectious Diseases
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Epidemiological StudiesDescriptive epidemiology
Careful tabulation of data concerning a diseaseRecord location and time of the cases of disease
Collect patient informationTry to identify the index case (or first case) of the disease
Epidemiology of Infectious Diseases
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Epidemiological StudiesAnalytical epidemiology
Seeks to determine the probable cause (etiology), mode of transmission, and methods of prevention
Useful in situations when Koch’s postulates can’t be applied
Often retrospective Investigation occurs after an outbreak has occurred
Epidemiology of Infectious Diseases
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Epidemiological StudiesExperimental epidemiology
Involves testing a hypothesis concerning the cause of a disease
Application of Koch’s postulates is experimental epidemiology
Endemic1: characteristic of or prevalent in a particular field, area, or environment2: restricted or peculiar to a locality or region“Endemic" means "in the population." "Endemic" is often used to characterize diseases that are generally found in a particular area; malaria, for example, is said to be endemic to tropical and subtropical regions. This use differs from that of the related word "epidemic" in that it indicates a more or less constant presence in a particular population or area rather than a sudden, severe outbreak within that region or group. The word is also used by biologists to characterize the plant and animal species that are only found in a given area.
EpidemicAffecting or tending to affect
a DISPROPORTIONATELY large number of individuals within a population, community, or region at the same time
DemographicsThe changes (such as the number of births,
deaths, marriages, and illnesses) that occur over a period of time in human populations; also : a set of such changes.
The demographics of a particular disease would include the ratio of males to females that have the disease, the average age, the geographical distribution, and the incidence (the likelihood of a person getting the disease) in a particular Country.
Epidemiology of Infectious Diseases
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Hospital Epidemiology: Nosocomial InfectionsTypes of nosocomial infections
Exogenous Pathogen acquired from the health care
environmentEndogenous
Pathogen arises from normal microbiota due to factors within the health care setting
Iatrogenic Results from modern medical procedures
Epidemiology of Infectious Diseases
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Hospital Epidemiology: Nosocomial InfectionsControl of nosocomial infections
Precautions designed to reduce factors that result in disease
Hand washing is the most effective way to reduce nosocomial infections
Epidemiology of Infectious Diseases
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Epidemiology and Public HealthAgencies at the local, state, national, and global level share information concerning diseaseThe United States Public Health Service
World Health Organization (WHO)Public health agencies work to limit disease transmissionMonitor water and food safety
Public health agencies campaign to educate the public on healthful choices to limit disease