•Introduction•Classification•Sources of infection•immunity•Factors influencing level of innate immunity •Exotoxins and endotoxins•Virulence determinants•Types of infectious diseases•Method of transmission of infection

Infection

PathogensSaprophytesParasitescommensals

Introduction

Primary infectionRe-infectionSecondary infectionFocal infectionCross infectionNosocromial infectionIatrogenic infection

Classification

Endogenous infectionExogenous infectionCLINICAL BASISUnapparent (subclinical)Atypical infectionLatent infection

Sources of infection

1. MAN: Carrier :- Healthy carrier Convalescent carrier Temporary or chronic carrier Contact carrier Paradoxical carrier2. ANIMAL : Asymptomatic, reservoir host Zoo noses3. INSECTS: Vectors, mechanical, biological, extrinsic incubation period4. SOIL AND WATER: Tetanus spores, H. capsulatuses, Water- vibrio cholerae, infective hepatitis5. FOOD- staphylococcus

Sources of infection in man

contact: direct- syphilis and gonorrhoeaContagious diseasesIndirect contact- fomitesInhalation: respiratory infection like tuberculosis,

influenza, small droplets (>0.1mm), droplet nuclei (1-10 microns diameter)

Ingestion:Inoculation: tetanus spores, rabies- s/cArbvirus- insect vectorsNeedles- iatrogenic- HIV AND HBVInsects: mechanical or biologicalcongenital Iatrogenic or laboratory infection

Methods of transmission of infection

AdhesionInvasivenessToxigenecity- toxinscommunicabilityOther bacterial products- coagulase haemolyseinBacterial appendages- e.g. capsulated organismsInfecting dose-MISD (minimum infecting dose) MLSD( minimum lethal dose)Route of infection

Virulence determinants (factors)

Bacteraemia- transient bacteraemiaSepticaemia- bacterial circulate and multiply

in bloods (high, swinging fever)Pyaemia- pyogenic bacteria causing

septicaemia leading to multiple abscesses in internal organs like spleen, liver, kidneys

Types of infectious diseases

endemicepidemicPandemicProsodemic- slowly creeping epidemics e.g.

CSF Fever

On the basis of spread of infectious diseases

EXOTOXINS ENDOTOINS

•Proteins •Protein polysaccharides, lipid complexes(PPL)

•Heat labile •Heat stable

•Actively secreted by cells, diffuse in surrounding medium

•Forms part of cell wall. do not diffuse

•Action often enzymic •No enzymic action

•Highly antigenic •Weakly antigenic

•Action specifically neutralized by antibodies

•Neutralization by antibodies ineffective

•Specific pharmacological effect for each exotoxin

•effect non specific action common to all endotoxin

•Specific tissue affinity •No specific tissue affinity

•can be toxoided • cannot be toxoided

•Separation from culture by physical methods e.g. filtration

•Obtained only by cell lysis

•Produced mainly by gram positive bacteria and some gram negative ones like Shigella ands vibrio

•Produced by gram negative bacteria

Distinguishing features of exotoxins and endotoxins