HOST PARASITE
RELATIONSHIP
Dr. Sudheer Kher
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 Infcetion
Endogenous Infection
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Exogenous Infection
Inapparent Infection
(Subclinical Infection)
Clinical Infection
Typical Infection
Atypical Infection
Latent Infection
SOURCES OF INFECTION
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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
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Other terms commonly used
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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
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Factors predisposing to Microbial
Pathogenicity
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Terms used
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Pathogenicity
Virulence
Exaltation
Attenuation
Factors
– Adhesion
» Adhesins
» Pili
– Invasiveness
– Toxigenicity
» Exptoxins
» Endotoxins
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Plasmids
Bacteriophages
Communicability
Bacterial appandages
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