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