The processes by which organisms cause disease to 2013.pptx

7/28/2019 The processes by which organisms cause disease to 2013.pptx

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The Processes by which Organisms

Cause Disease to Host Tissue

(Pathogenesis)

Champa Ratnatunga

Department of Microbiology

Infection -1 2/4/2013


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Objectives

Define the term pathogenesis, immuno

pathogenesis

List currently known modes of transmission

microbial entry

Describe essential steps in microbial infection

attachment, invasion, mechanisms of damage

Explain how common clinical manifestations ofinfections reflect these mechanisms of damage in

various organs


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Pathogenesis-The mechanisms by which a disease

occurs

Pathogenthe organism causing the disease Pathogenicity the ability/ capacity to cause disease

Commensal/ Normal flora organism that lives on

or in the host/ human body normally without

causing disease

Colonizerorganism that colonizes the host /human

body but does not cause disease (these may be acquired

from new environments or be part of normal flora)

Colonizer PathogenChanges in the body defenses or flora


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To be a pathogen -

Transmissibility / communicability

Survival in the new host

Infectivity ability to breach the new hosts

defenses Virulence capacity of the pathogen to harm the

host.

2 types of pathogen Primary pathogen cause disease in healthy persons

Opportunistic pathogens - cause disease in impairedhost defenses

Strict pathogen ----------------------------------------


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Pathogenesis Important because-

.................................................................................

..

Infection- includes both the multiplication of theorganism within the host, invasion of a tissue byorganisms as well as the sequelae caused by theinfection even if the organism is no longer present

Signs and symptoms (disease) may or may not be seen

Natural history of a disease how the diseaseprogresses over time if not treated.


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Immuno - pathogenesis

Pathogen Invades Host/Human body

Immune system isactivated as defense

Immune system acts

against the pathogen

to destroy it

The immune reaction can cause damage

to the host tissue as well.

Ex: Wucheraria bancrofti - Elephantiasis


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Modes of Entry into the human body

Through respiratory tract aerosols / droplets

Direct contact with skin - intact or broken skin

Ingestion to GI tract

Genito urinary tract ascending infection

Exchange of body fluids (blood/ secretions) Injection by vectors

Sources

o Other humanso Animal reservoir

o Environment


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To cause disease

Colonization

Invasion

Avoidance of host defense mechanisms method/s of causing damage to tissue

Factors that help the bacterium to do these -


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Surface molecules and structural molecules

Many different molecules on the surface of bacteria/

viruses/fungi as well as on the surface of animal(human) cells.

Molecules are part of the normal (cell wall or internal)

structure of the organism.

have many functions including cell signaling ,binding to tissues/ organisms, activating

pathways, blocking pathways, identifying cell aspart of the body or from a different animal or asa pathogen by other cells.


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These can be proteins/ lipids/CHO or combinationsof them (glycopeptides/ lipoprotein).

Some of these molecules will play a part inpathogenesis.

They can also be useful in the identification ofbacteria with lab tests. (form the basis of someclassification systems of bacteria as the mostconvenient classification system for themicrobiologist is one that is based on the tests)


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Virulence factors - Virulence factors help bacteria to

(1) invade the host

(2) cause disease

(3) evade host defenses.

These can be surface molecules or structures of the organism thathelp it to cause disease by

help the organism attach to the cell it wants to infect

block host cells from identifying the microbe as a pathogen make the microbe motile

block the activation of our defense pathways etc.

- they can also be chemicals (enzymes, toxins) that the pathogenactively secretes in order to cause disease by damaging host tissue

-single organism can cause disease in different ways (tissueinfection/ toxin mediated/ immune mediated)


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Attachment / adhesion For colonization of mucosal surface adhesion

To avoid innate defenses Peristalsis of GIT

Flushing action mucus, saliva, urine

To acquire essential nutrient ex-Iron

Adhesion surface interactions between specificreceptors on the host cell membrane and ligands on thebacterial surface. contributes to tissue specificityof infection

Pathogenesis induces structural and functional changesin mucosal cells

exEntero pathogenic Escherichia coli (EPEC)

H pylori


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Invasion

Pathogenic effects can be by

Invasion bacterium invades host cell, multiplies,

lyses host cell and spreads to adjacent/ deeper

tissue.

Ex: Mycobacteria, Salmonella, Shigella, Escherichia,Neisseria

Without invasion toxins and induction of intra-

cellular signaling pathways mediate damage at

local or distant sites.


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Avoidance of host defenses Capsules polysaccharide capsules reduce efficiency of

phagocytosis

H influenzae, N meningitidis, S pneumoniae, Intracellular pathogens hide inside host cells

Leishmania, toxoplasma macrophages

PlasmodiumRBCs

Streptococcal M protien-..

Resistance to killing by phagocytic cells Mycobacteria prevents phago-lysosome fusion

S aureus produces catalase to neutralize effect of toxic O2radicals.

Immunoglobulin A proteases-.

Mimic host antigens Extracellular parasites

Keep changing antigens-host produces a lot of useless antibodies ex-Schistosomes


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Toxins

Endotoxin (LPS) component of the outer

membrane of gram negative bacteria Effects of endotoxin - .

Exotoxinsdiffusible proteins secreted into the

external medium by the pathogen. Cholera toxin promotes fluid and electrolyte excretion

from enterocytes without killing the cell.

Diptheria toxin mediates cell death

Tetanus toxin effect on skeletal muscle Shigella toxin Bacillary dysentry

Streptolysin O and S lysis of blood cells


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Enzymes

Mucinases

Phospholipases

Collagenases Hyaluronidases

Coagulase

Streptokinase


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Damage to cells and tissue

Damage to local tissue

Invasion and lysis of cells

Enzyme and toxin mediated destruction

Inflammatory reaction

Damage to distant tissue

Toxins -


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Pictures of microbial invasion of living tissue

(E coli invasion of renal tissue)


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Signs and symptoms in relation to the

mechanisms of pathogenesis

Pain, warmth, swelling, redness, loss of functionACUTE INFLAMMATION immune reaction

Nasal secretions when having a cold exudate dueto inflammation

Fever pyrexins

Diarrhoea toxin/ damage to gut epithelium Diarrhoea with blood indicates invasion of the gut

epithelium.

Abscess Pus formation due to large neutrophilresponse to some bacteria

Endotoxin toxin mediated shock


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Summary

Pathogenesis is the process/s by which

organisms cause disease.

Virulence factor factors that help the

organism to cause disease

Adherence , invasion, avoidance of host

defenses, toxins and enzymes


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When you learn about an organism

Name and type (classification)

Mode of transmission / reservoirs / hosts

Virulence factors Intra / extra cellular, capsule/

enzymes and toxins etc Types of disease and pathogenesis in relation to

signs and symptoms

Risk groups / opportunistic

http://www.life.umd.edu/classroom/bsci424/HostParasiteInteractions/HostParasiteSummary.htm


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The processes by which organisms cause disease to 2013.pptx

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