Infection Infection

Infectious process Infectious process

Genle-Koch’s postulates Genle-Koch’s postulates

The microorganism must be present in every The microorganism must be present in every case of the disease and not be isolated from case of the disease and not be isolated from healthy human or from human with other healthy human or from human with other disease disease The microorganisms must be grown in pure The microorganisms must be grown in pure culture from the sick hostculture from the sick hostThe same disease must be reproduced when a The same disease must be reproduced when a pure culture of the microorganism is inoculated pure culture of the microorganism is inoculated into a healthy, susceptible host (animal)into a healthy, susceptible host (animal)The microorganism must then be recovered from The microorganism must then be recovered from the experimentally infected host the experimentally infected host

Infection (infectious process)Infection (infectious process)

It is a historically formed complex of It is a historically formed complex of biologic events and processes that are biologic events and processes that are occurred in organism when pathogenic occurred in organism when pathogenic microorganism penetrates and microorganism penetrates and reproduces in it reproduces in it

Components of infectious process Components of infectious process

Organism

Conditions of

interaction

Infectiousagent

Pathogenicity Pathogenicity

It is a genetically conditioned It is a genetically conditioned possibility of microorganisms to cause possibility of microorganisms to cause infectious processinfectious process

Categories of pathogenic Categories of pathogenic microorganisms microorganisms

True pathogensTrue pathogens (primary pathogens) are (primary pathogens) are capable of causing infection and disease capable of causing infection and disease on healthy person with normal immune on healthy person with normal immune defensesdefenses

Opportunistic pathogensOpportunistic pathogens cause disease cause disease when the host’s immune system is when the host’s immune system is compromisedcompromised

Classification of pathogenic Classification of pathogenic microorganisms microorganisms

Pathogenic microbes

Obligate intracellular Facultative intracellular

Obligate extracellular

Virulence Virulence

It is a quantitative characteristic of degree It is a quantitative characteristic of degree of microorganism pathogenicity of microorganism pathogenicity

Virulence factors Virulence factors

Adhesion Adhesion Colonization Colonization Invasion Invasion Penetration Penetration Toxigenicity Toxigenicity Factors of aggressive Factors of aggressive

Virulence factors are properties of disease-causing microorganism, that enhance their pathogenicity and allow them to colonize or to invade human tissue and disrupt normal body functions

Pathogenesis Pathogenesis

It is a complex of reactions and It is a complex of reactions and mechanisms that are characterized mechanisms that are characterized interaction between human organism interaction between human organism and microorganisms during infectious and microorganisms during infectious processprocess

A generalized sequence of the A generalized sequence of the stages of infection stages of infection

1. Transmission from an external source into the portal of entry1. Transmission from an external source into the portal of entry

2. Adherence to mucous membranes2. Adherence to mucous membranes

3. Colonization by growth of the bacteria at the site of 3. Colonization by growth of the bacteria at the site of adherenceadherence

4. Invasion4. Invasion

5. Forming of primary inflammatory nidus 5. Forming of primary inflammatory nidus

6. Spread agents in the organism 6. Spread agents in the organism

7. Disease symptoms caused by toxin production or invasion7. Disease symptoms caused by toxin production or invasion

8. Host responses, both nonspecific and specific8. Host responses, both nonspecific and specific

9. Progression or resolution of the disease9. Progression or resolution of the disease

Reservoir of infection Reservoir of infection

Sick human (syphilis)Sick human (syphilis)

Sick animal (rabies)Sick animal (rabies)

Carriers (salmonellosis)Carriers (salmonellosis)

Soil (fungal disease, actinomycetal disease) Soil (fungal disease, actinomycetal disease)

It is the primary habitat in the nature world from which a pathogen originates

The infectious dose (ID)The infectious dose (ID) refers to the refers to the minimum number of microbial cell required minimum number of microbial cell required to initiate infection in the host. to initiate infection in the host.

Sours of infectious agentSours of infectious agent

Exogenous.Exogenous. When agents is originating from a When agents is originating from a source outside the body (the environment or source outside the body (the environment or another person or animal)another person or animal)

EndogenousEndogenous. . Already existing on or in the Already existing on or in the body (normal flora or latent infection)body (normal flora or latent infection)

Mechanisms of transmissionMechanisms of transmission

Horizontal transmissionHorizontal transmission is the spread of is the spread of infectious disease from person to personinfectious disease from person to person

Vertical transmissionVertical transmission is the spread of is the spread of infectious disease from parent to offspring during infectious disease from parent to offspring during pregnancy or deliveringpregnancy or delivering

Disease transmissionDisease transmission

Airborne transmissionAirborne transmission (influenza, tuberculosis, (influenza, tuberculosis, diphtheria)diphtheria)

Food and waterborne transmissionFood and waterborne transmission (botulism, (botulism, typhoid fever, hepatitis A)typhoid fever, hepatitis A)

Vector transmissionVector transmission (yellow fever, lime disease, (yellow fever, lime disease, viral encephalitis)viral encephalitis)

Sexually transmittedSexually transmitted diseasedisease (syphilis, (syphilis, gonorrhea, genital herpes, AIDS)gonorrhea, genital herpes, AIDS)

Disease transmitted through direct skin Disease transmitted through direct skin contactcontact (leprosy)(leprosy)

Portal of entry Portal of entry

Mucous membrane of gastrointestinal tract (Mucous membrane of gastrointestinal tract (Salmonella typhi, Salmonella typhi, Shigella dysenteria, Hepatitis A virus)Shigella dysenteria, Hepatitis A virus)

Mucous membrane of respiratory tract Mucous membrane of respiratory tract (Neisseria meningitidis, (Neisseria meningitidis, Mycobacterium tuberculosis, Influenza virus)Mycobacterium tuberculosis, Influenza virus)

Mucous membrane of urinary and genital tract Mucous membrane of urinary and genital tract (Neisseria (Neisseria gonorrhoeae, Treponema pallidum)gonorrhoeae, Treponema pallidum)

Skin (native and hurt) Skin (native and hurt) (Leptospira interrogans, Clostridium (Leptospira interrogans, Clostridium tetani)tetani)

The portal of entryThe portal of entry is the site at which a is the site at which a microorganism first contacts host susceptible microorganism first contacts host susceptible tissue through that microbe can penetrate into tissue through that microbe can penetrate into the organismthe organism

Mechanisms of pathogen adhesionMechanisms of pathogen adhesion

Adherence of bacteria Adherence of bacteria

Vibrio holerae on the surface of enterocytes

Gonococci on the surface of urinary epithelium

Action of enzymes Action of enzymes

Exoenzymes dissolve extracellular barrier and make possible penetration of bacteria through or between cells to underlying tissues

Collagenase and hyaluronidase, which degrade collagen and hyaluronic acid, respectively, thereby allowing the bacteria to spread through subcutaneous tissue.

Pathogenic enzymes Pathogenic enzymes

Enzyme Enzyme Function Function

PhospholipasePhospholipase Breaks down lecithin, a lipid component of Breaks down lecithin, a lipid component of mammalian cell membranemammalian cell membrane

Coagulase Coagulase Coagulates plasma; blood clotsCoagulates plasma; blood clots

Collagenase Collagenase Breaks down collagen (connective tissue Breaks down collagen (connective tissue fiber)fiber)

Hyaluronidase Hyaluronidase (spreading factor)(spreading factor)

Breaks down hyaluronic acid, a tissue Breaks down hyaluronic acid, a tissue component component

Lipase Lipase Breaks down fat Breaks down fat

Lecithinase Lecithinase Destroys red blood cells and other tissue Destroys red blood cells and other tissue cellscells

Deoxyribonuclease Deoxyribonuclease Breaks down DNABreaks down DNA

Fibrinolysin Fibrinolysin Dissolves blood clots Dissolves blood clots

Definition Definition

Bacteremia.Bacteremia. Indicating the presence of bacteria in Indicating the presence of bacteria in the blood, usually transient the blood, usually transient Viremia.Viremia. Indicating the presence of viruses in the Indicating the presence of viruses in the bloodblood..ToxemiaToxemia.. Indicating the presence of bacterial toxins Indicating the presence of bacterial toxins in the bloodin the bloodSepsis.Sepsis. Stage of infectious process when agent is Stage of infectious process when agent is not only present in the blood, but can multiply therenot only present in the blood, but can multiply thereSepticopyemia.Septicopyemia. When agent is not only multiply in When agent is not only multiply in the blood, but and can form purulent nidus in the blood, but and can form purulent nidus in organs and tissues of sick humanorgans and tissues of sick human..

Effects of exotoxins and endotoxinsEffects of exotoxins and endotoxins

Action of toxins Action of toxins

Exotoxins diffuse to target cells, which are poisoned and disrupted

Differential characteristics of bacterial Differential characteristics of bacterial exotoxins and endotoxins (1)exotoxins and endotoxins (1)

PropertyProperty Exotoxin Exotoxin Endotoxin Endotoxin

Source Source A few gram-positive and A few gram-positive and gram-negative bacteriagram-negative bacteria

Most of gram-Most of gram-negative bacteria negative bacteria

Manner of Manner of releaserelease

Secreted from live cellSecreted from live cell Released by cell Released by cell during lysisduring lysis

Chemical Chemical Polypeptide Polypeptide Lipopilysaccharide Lipopilysaccharide (LPS)(LPS)

Location of Location of genesgenes

Bacterial chromosome, Bacterial chromosome, plasmid or bacteriophageplasmid or bacteriophage

Bacterial Bacterial chromosomechromosome

Heat stability Heat stability Destroyed rapidly at 60Destroyed rapidly at 6000CC Stable at 100Stable at 10000C for 1 C for 1 hourhour

Differential characteristics of bacterial Differential characteristics of bacterial exotoxins and endotoxins (2)exotoxins and endotoxins (2)

PropertyProperty Exotoxin Exotoxin Endotoxin Endotoxin Toxicity Toxicity High (toxic in minute High (toxic in minute

amounts)amounts)Low (toxic in high Low (toxic in high dose)dose)

Clinical Clinical effects effects

Specific to a cell type Specific to a cell type Systemic: fever, Systemic: fever, inflammationinflammation

Fever Fever stimulationstimulation

Usually notUsually not Yes Yes

Antigenicity Antigenicity High. Induces high titer High. Induces high titer antibodies called antitoxinsantibodies called antitoxins

Low. Poorly Low. Poorly antigenic antigenic

Toxoid Toxoid formationformation

Convert to toxoid that used Convert to toxoid that used as vaccines as vaccines

Do not convert to Do not convert to toxoidtoxoid

Classification of exotoxins based Classification of exotoxins based on mechanism of actionon mechanism of action

Type of Type of toxintoxin

General site and mode of General site and mode of action action

Bacterium-Bacterium-producerproducer

Neurotoxin Neurotoxin Interference with nerve transmission Interference with nerve transmission Clostridium Clostridium botulinum botulinum

Enterotoxin Enterotoxin Inflammation of the gastrointestinal Inflammation of the gastrointestinal tract; typically causes excessive tract; typically causes excessive secretions of fluid and electrolytes from secretions of fluid and electrolytes from the lining of the gastrointestinal tractthe lining of the gastrointestinal tract

Vibrio cholerae Vibrio cholerae

Cytotoxin Cytotoxin Causes cell death, often by lysis and/or Causes cell death, often by lysis and/or interference with protein synthesisinterference with protein synthesis

Corynebacte-Corynebacte-rium diphtheriaerium diphtheriae

Hemolysin Hemolysin Cytotoxin that causes the lysis of Cytotoxin that causes the lysis of human erythrocytes and some other human erythrocytes and some other cells.cells.

Staphylococcus Staphylococcus aureus aureus

Effects of endotoxin Effects of endotoxin

Clinical findings Clinical findings Mediator or mechanismMediator or mechanism

Fever Fever Interleukin-1Interleukin-1

Hypotension Hypotension (shock)(shock)

Bradykinin, nitric oxideBradykinin, nitric oxide

Inflammation Inflammation Alternative pathway of Alternative pathway of complement (C3a,C5a)complement (C3a,C5a)

CoagulationCoagulation Activation of Hageman factor Activation of Hageman factor

Factors of aggressiveFactors of aggressive

Capsule. Prevents phagocyte from adhering to the bacterium

Cell wall protein of gram-positive cocci, such as the M protein of Streptococcus pyogenes and protein A of St. aureus.

Infectious disease Infectious disease

It is an extreme extent of infectious It is an extreme extent of infectious process when precise clinical sings occur process when precise clinical sings occur and pathologic changes in an organism and pathologic changes in an organism are present are present

Types of infection Types of infection Localized.Localized. Restricted to a confined area in the bodyRestricted to a confined area in the body

Systemic.Systemic. An infection in which the microorganisms spread An infection in which the microorganisms spread throughout the bodythroughout the body

Primary.Primary. Caused by one type of microorganismsCaused by one type of microorganisms

Secondary.Secondary. Caused by a microorganism followingCaused by a microorganism following a a primary primary infectioninfection

Mixed.Mixed. An infection caused by two or more microorganismsAn infection caused by two or more microorganisms

Subclinical.Subclinical. An infection that does not display any symptoms An infection that does not display any symptoms

Acute.Acute. An infection that appears suddenly, has a short course, An infection that appears suddenly, has a short course, is relatively severeis relatively severe

Chronic.Chronic. An infection that persist over a long period of time An infection that persist over a long period of time with or without symptomswith or without symptoms

Type of infection caused by one species Type of infection caused by one species of microorganismsof microorganisms

ReinfectionReinfection occurs when the human was infected by occurs when the human was infected by

microorganism of same species after recoverymicroorganism of same species after recovery

Superinfection Superinfection occurs when the human was infected by occurs when the human was infected by

microorganism of same species during infectious processmicroorganism of same species during infectious process

RelapceRelapce occurs when symptoms of disease are occurs when symptoms of disease are appeared without exogenous infecting appeared without exogenous infecting

Recovered Reinfection

Sick Superinfection

Relapce Asymptomatic

Types of infection Types of infection

Typical stages of an infectious Typical stages of an infectious disease disease

1.1. The incubation periodThe incubation period, , which is the time between the which is the time between the acquisition of the microorganisms (or toxin) and beginning acquisition of the microorganisms (or toxin) and beginning of symptoms of symptoms

2.2. The prodromal periodThe prodromal period, during which nonspecific , during which nonspecific symptoms such as fever, malaise, and loss of appetite symptoms such as fever, malaise, and loss of appetite occuroccur

3.3. The specific-illness (clinical) periodThe specific-illness (clinical) period , during which the , during which the overt characteristic signs and symptoms of the particular overt characteristic signs and symptoms of the particular disease occurdisease occur

4.4. The recovery periodThe recovery period, during which the illness abates , during which the illness abates and the patient returns to the healthy stateand the patient returns to the healthy state

Stages of infectious diseaseStages of infectious disease