HOST PARASITE RELATIONSHIP

Dr. Sudheer Kher

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Range of relationships Saprophytes Parasites Commensals Pathogens

Terms used   

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Primary Infection Reinfection Secondary Infection Focal Infection (Focal Sepsis) Generalized Infection Cross Infection Iatrogenic Infection Endogenous Infection

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Exogenous Infection Inapparent Infection (Subclinical Infection) Clinical Infection Typical Infection Atypical Infection Latent Infection

SOURCES OF INFECTION 

Human Beings

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– Patients – Carriers » Healthy » Convalescent » Temporary » Chronic » Contact » Paradoxical

Animals – Zoonosis – Reservoir

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Insects – Mechanical – Biological

Soil & Water  Food 

Other terms commonly used    

Endemic Epidemic Pandemic Prosodemic

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Bacteremia – Common occurrence while brushing, chewing etc

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Septicemia – Circulation, multiplication, formation of toxins with high swinging fever

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Pyemia – – Septicemia by pyogenic organisms. Produces multiple abscesses in internal organs.

METHODS OF TRANSMISSION OF INFECTION Contact  Congenital  Inhalation  Ingestion  Inoculation  Insects  Iatrogenic  Lab Acquired 

Factors predisposing to Microbial Pathogenicity 

Terms used – – – –

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Pathogenicity Virulence Exaltation Attenuation

Factors – Adhesion » Adhesins » Pili

– Invasiveness

– Toxigenicity » Exotoxins » Endotoxins

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Plasmids Bacteriophages Communicability Bacterial appendages Infecting dose » MID ID50 » MLD LD50

– Route of Infection

Exo

Vs Endotoxins

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Protein

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Heat Labile Secreted by cells. Diffuse out Separable by filtration Enzymatic action Specific effect Specific tissue affinity Active in small qty Highly antigenic Action neutralized by specific antibody Can be toxoided Mainly produced by Gram + bacteria. Few Gram - bact

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Protein-Polysaccharide-Lipid Complex

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Heat Stable Part of cell wall. No diffusion Obtained only by cell lysis No Enzymatic action Effect non-specific Non-specific Active in large doses Weakly antigenic

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Antibody does not neutralize

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Can not be toxoided Produced by Gram negative bacteria

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Biological activities of the Endotoxins   

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Pyrogenicity Lethal action  Blood Pressure Activation of complement Intravascular coagulation Leucopoenia / Leukocytosis

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 Glucose / Glycogen synthesis in Liver Stimulation of B cells Macrophage inhibition Interferon release Induction of prostaglandin synthesis Clotting of Limulus Lysate