infection
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INFECTION INFECTION
AND AND
PATHOGENECITY PATHOGENECITY
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1. Saprophytes.1. Saprophytes.
Free living in water, soil. Free living in water, soil.
No multiplication. No multiplication.
No infectious disease No infectious disease
Except B. subtilis. Except B. subtilis.
2.Pathogens:2.Pathogens:
3. Commensals 3. Commensals Opportunistic pathogensOpportunistic pathogens
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Classification of microbesClassification of microbes
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DefinitionDefinitionInvasion (entry,fixation) Invasion (entry,fixation) and multiplication of and multiplication of microbes in body tissues, microbes in body tissues, which may be clinically which may be clinically unapparent or result in unapparent or result in local cellular injury due to local cellular injury due to competitive metabolism, competitive metabolism, toxins, intracellular toxins, intracellular replication or antigen replication or antigen
antibody response.antibody response.
All infections not results All infections not results in Infectious disease.in Infectious disease.
Classification of infections Classification of infections 1.Based on Occurrence:1.Based on Occurrence:
a).Primary infection:a).Primary infection: Infection is first time with a Infection is first time with a
microbe. microbe.
b).Reinfection:b).Reinfection: Subsequent infections with same Subsequent infections with same
microbe.microbe.
c).Secondary infection:c).Secondary infection: Infection followed by lowered HostInfection followed by lowered Host
immunity by preexisting disease.immunity by preexisting disease. 4
d).d).Focal infection:Focal infection:
Localized infection with generalized Localized infection with generalized
symptoms. symptoms. Ex: Appendicitis, TonsillitisEx: Appendicitis, Tonsillitis
e).Cross infection:e).Cross infection:
New infection in a patient from another New infection in a patient from another
host or source.host or source.
f).Nosocomial infection:f).Nosocomial infection:
If cross infections occur in hospitalized If cross infections occur in hospitalized
individual (Hospital acquired infection).individual (Hospital acquired infection). 5
g).g). Iatrogenic infection:Iatrogenic infection: Infections by means of Infections by means of InvestigativeInvestigative & & therapeutic therapeutic procedures. procedures.
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Based on Based on sourcesource
Endogenous:Endogenous:
From Normal From Normal
flora. flora.
Exogenous: Exogenous:
Another Another
individual.individual.
EnvironmentEnvironment. .
Based on clinical Based on clinical effects:effects:Inapparent (Sub clinical):Inapparent (Sub clinical):
No S/S in spite of No S/S in spite of infection. infection.
Atypical infection: Atypical infection: Absence of typical Absence of typical
manifestations. manifestations.
Latent infectionLatent infection:: Followed by infection- Followed by infection-
Microbe Microbe retainretain in tissues. in tissues.
Starts proliferation with Starts proliferation with
lowered immunity. lowered immunity. 7
1.HUMAN BEINGS1.HUMAN BEINGS
Commonest source. Commonest source.
Infective agentInfective agent
transferred either transferred either
fromfrom
PatientPatient or from or from
Carrier.Carrier.
SOURCES OF SOURCES OF INFECTIONINFECTION
Types of carrier:Types of carrier:
Depending on origin:Depending on origin:
A. Healthy carrier A. Healthy carrier
B. Convalescent B. Convalescent carriercarrier
C. Contact carrier:C. Contact carrier:
Acquires pathogen Acquires pathogen
from patient.from patient.
D. Paradoxical carrier.D. Paradoxical carrier.
Acquires pathogen Acquires pathogen
from another from another CarrierCarrier. .
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Based on the duration Based on the duration of carriageof carriage …… ……
A. Temporary A. Temporary
carrier:carrier: Microbes harbors Microbes harbors notnot
more than 6 more than 6 months. months.
B.B.Chronic carrier:Chronic carrier:
Microbes harbors Microbes harbors
several yearsseveral years or or even even
for life. for life.
2. INSECTS2. INSECTS
VECTOR.VECTOR.
a). Mechanical a). Mechanical
vectors.vectors.
b).b). Biological Biological
vectors. vectors.
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“ “ Arthropod borne Arthropod borne diseases ” diseases ”
3).ANIMALS:3).ANIMALS:
Infectious diseases transmitted from Infectious diseases transmitted from
animals to man. animals to man. ZOONOSES.ZOONOSES.
a).Bacterial:a).Bacterial: Leptospira, plague from Rat. Leptospira, plague from Rat.
b).Viral :b).Viral : Rabies from dog. Rabies from dog.
c).Protozoa:c).Protozoa: Leishmaniasis from dog. Leishmaniasis from dog.
d).Helminthsd).Helminths : : Hydatid disease from dog Hydatid disease from dog
Tape worms : Cattle , Pig.Tape worms : Cattle , Pig.
e).Fungal:e).Fungal: Zoophilic dermatophytes - Dog. Zoophilic dermatophytes - Dog. 10
4)4) SOIL & WATERSOIL & WATER
Soil :Soil : Spores of Tetanus bacilli Spores of Tetanus bacilli
Histoplasma and Nocardia spp. Histoplasma and Nocardia spp.
Water: Water: Cholera, H A V , H E V, Cholera, H A V , H E V,
Typhoid etc. Typhoid etc.
5)5) FOODFOOD
Contaminated food. Contaminated food.
Ex: Staphylococci, Cl. Botulinum. Ex: Staphylococci, Cl. Botulinum.
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1.Contact:1.Contact:
i) Directi) Direct ex: STDs. ex: STDs.
ii) Indirect :ii) Indirect :
Through Through
contaminated contaminated
fomites like Toys, fomites like Toys,
Pencils, Clothing. Pencils, Clothing.
Ex: Diphtheria, Ex: Diphtheria,
Trachoma.Trachoma.
METHODS OF TRANSMISSIONMETHODS OF TRANSMISSION
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2.2. InhalationInhalation • Secretions from Secretions from
Respiratory tract Respiratory tract
infections. infections.
(Sneezing, Speaking, (Sneezing, Speaking,
Coughing) Coughing)
DROPLET NUCLEI DROPLET NUCLEI
& AEROSOLS& AEROSOLS
Ex: H. Ex: H. influenza, influenza,
Tubercle Tubercle bacilli. bacilli.
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3.3. Ingestion:Ingestion: Through food & water. Through food & water.
Ex: Cholera, Ex: Cholera, Dysentery, Dysentery,
Food Food poisoning with poisoning with
B. cereus, B. cereus,
Staphylococci.Staphylococci.
4.4. Inoculation:Inoculation: Pathogen injected into Pathogen injected into
tissues. tissues.
Ex:Tetanus spores.Ex:Tetanus spores.
ArbovirusesArboviruses(Insects).(Insects).
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5.5.Congenital Congenital transmission:transmission:
(Transplacental ,(Transplacental ,
Vertical transmission)Vertical transmission)
Placental defects results in Placental defects results in
Congenital transformation Congenital transformation
of microbes and results inof microbes and results in
malformations.malformations.
((Teratogenic infections ).Teratogenic infections ).
Ex : Ex : To R C HTo R C H complex complex..
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7. Iatrogenic infections7. Iatrogenic infections Procedures like….Procedures like….
Dialysis,Dialysis,
Transfusions,Transfusions,
Heart Surgery,Heart Surgery,
Transplant Surgery, Transplant Surgery,
Injections. Injections.
Lumbar puncture.Lumbar puncture.
CatheterizationCatheterization. . 16
DETERMINANTS OF DETERMINANTS OF PATHOGENICITYPATHOGENICITY
Pathogenicity:Pathogenicity:
Disease producing capacity ofDisease producing capacity of
species.species.Virulence:Virulence:
Disease producing capacity of Disease producing capacity of
a a strain.strain.Exaltation:Exaltation:
Enhancement of pathogenicity.Enhancement of pathogenicity.Attenuation:Attenuation:
Retaining antigenicity andRetaining antigenicity and
loss of pathogenicity.loss of pathogenicity. 17
1.1. Adhesion:Adhesion: AdhesionsAdhesions..
Fimbriae, PiliFimbriae, Pili (Colonization factor) (Colonization factor)..
Prevents flushing away process. Prevents flushing away process.
High concentration of toxins. High concentration of toxins.
Facilitates penetration into host cells. Facilitates penetration into host cells.
All are antigenic in nature.All are antigenic in nature.
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2.2. Invasiveness:Invasiveness: Ability of an organism to invade the host Ability of an organism to invade the host
cells after establishing the infection. cells after establishing the infection.
Antiphagocytic factors-Antiphagocytic factors-
Capsule, Streptococcal ‘M’ protein. Capsule, Streptococcal ‘M’ protein.
Cytotoxins:Cytotoxins:Haemolysins, Leucocidins.Haemolysins, Leucocidins.
Bacterial surface antigens. Bacterial surface antigens.
Vi antigen ,K antigen. Vi antigen ,K antigen.
Enzymes:Enzymes:Coagulase. Coagulase.
Hyaluronidase & Collaginase.Hyaluronidase & Collaginase.
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3.Toxigenicity:3.Toxigenicity:
Toxin Toxin producing capacity.producing capacity. ExotoxinsExotoxins
EndotoxinsEndotoxins
SuperantigensSuperantigens
ExotoxinExotoxin Endotoxin Endotoxin
-Proteins. Proteins. - Protein ,Polysaccharide - Protein ,Polysaccharide &&
lipidlipid
-Heat labile. Heat labile. - Heat stable.- Heat stable.
-Secreted by cells Secreted by cells - Part of cell wall. - Part of cell wall.
-Separable from culture. Separable from culture. - Only by cell lyses.- Only by cell lyses.
-Enzymatic action. Enzymatic action. - No enzymatic action. - No enzymatic action.
-Effect is -Effect is - Non specific- Non specific..Specific
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-Tissue specific. Tissue specific. - Not. - Not.
-Active in doses. Active in doses. - doses.- doses.
-Highly antigenic. Highly antigenic. - Weakly…. - Weakly….
-Neutralized by antibody Neutralized by antibody - But not….- But not….
-Can be Can be - Cannot be… - Cannot be…
-Produced by Gram positive Produced by Gram positive - Gram negative.- Gram negative. bacteriabacteria bacteria bacteria Except:Except: Shigella, Cholera, Shigella, Cholera,
E T E C.E T E C.
Minute Large
Toxoided
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4.4. Plasmids:Plasmids:
R R - factor- factor E. coli. → E. coli. → Enterotoxin.Enterotoxin.
Toxins from Staph. aureus. Toxins from Staph. aureus.
5.5. Communicability:Communicability:
Ability of a pathogen to intoAbility of a pathogen to into community.community.
High for Respiratory, Intestinal infections. High for Respiratory, Intestinal infections.
Spread
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7.7. Infecting dose:Infecting dose: M I D :M I D : Minimum infecting dose. Minimum infecting dose.
M L D :M L D : Minimum lethal dose. Minimum lethal dose.
8.8. Bacteriophages:Bacteriophages:
• Viral particles infecting bacteria.Viral particles infecting bacteria.
Ex: Ex: Diphtheria toxin.Diphtheria toxin.
9.9. Route of infection:Route of infection: Streptococci:Streptococci: Any route. Any route.
Cholera:Cholera: Oral route only. Oral route only.25
TYPES OF INFECTIOUS DISEASESTYPES OF INFECTIOUS DISEASES
1. 1. Depending on location:Depending on location:
Superficial Superficial
a). Localizeda). Localized
Deep seated.Deep seated.
b). Generalized.b). Generalized.
Bacteremia :Bacteremia :
Septicemia :Septicemia : Bacteria + Toxins. Bacteria + Toxins.
Pyemia :Pyemia :
Bacteria , Toxins and Multiple Bacteria , Toxins and Multiple
abscesses in internal organs. abscesses in internal organs.
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2. Depending on Spread :2. Depending on Spread : A. Endemic :A. Endemic :
Constantly present in a Constantly present in a
particular area. particular area.
Ex: Typhoid, Malaria.Ex: Typhoid, Malaria.
B. Epidemic :B. Epidemic :
Rapid spread with involvingRapid spread with involving
many persons. many persons.
Ex: Influenza.Ex: Influenza.
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3.3. Pandemic:Pandemic:
Epidemic , that spreads many parts of Epidemic , that spreads many parts of
the world within a short time.the world within a short time.
Ex :Ex :Influenza, Cholera, Influenza, Cholera,
Plague, Viral conjunctivitis. Plague, Viral conjunctivitis.
4. Prosodemic:4. Prosodemic:
Slowly spreading epidemic. Slowly spreading epidemic.
Ex : Ex : Cerebrospinal fever. Cerebrospinal fever.
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BE AWARE
of INFECTIONS
& INFECTIOUS DISEASES
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