■ Principles of Infection & Classification of
Diseases
1. Principles of Establishment of Infection
- Tissue Damage – direct destruction of host cells (e.g., Entamoeba histolytica).
- Release of Toxins – exotoxins (Clostridium botulinum), endotoxins (E. coli).
- Obstruction of Vessels – filarial worms causing elephantiasis.
- Variation of Surface Antigens – Trypanosoma, Neisseria gonorrhoeae.
- Antigenic Mimicry – Streptococcus pyogenes M protein.
- Production of Enzymes – hyaluronidase, collagenase, coagulase, fibrinolysin.
- Destruction of Host Tissues – via cytotoxins or immune damage.
2. Classification of Infectious Diseases
A. Based on Organ System Involved:
- Gastrointestinal – Cholera, Salmonellosis, Dysentery.
- Respiratory – Pneumonia, Tuberculosis, Influenza.
- CNS – Meningitis, Encephalitis, Brain abscess.
- Cardiovascular – Endocarditis, Myocarditis, Pericarditis.
- Sepsis – bloodstream invasion, septicemia, septic shock.
- Skin/Soft tissue – Cellulitis, Necrotizing fasciitis.
- Genitourinary – UTIs, STIs.
B. Based on Microbiology:
- Bacterial – Gram + (Staphylococcus, Streptococcus), Gram - (E. coli, Salmonella), Mycobacteria.
- Fungal – Superficial (Ringworm), Subcutaneous (Sporotrichosis), Systemic (Histoplasmosis).
- Viral – DNA viruses (Herpesvirus, Hepatitis B), RNA viruses (HIV, Influenza).
- Parasitic – Protozoa (Plasmodium, Giardia), Helminths (Schistosoma, Taenia), Ectoparasites
(Lice, Mites).
- Prion – Scrapie, Creutzfeldt–Jakob disease, Mad cow disease.
3. Biological Properties of Pathogens
- Infectivity – ability to enter and multiply.
- Pathogenicity – ability to cause disease.
- Virulence – severity of disease.
- Immunogenicity – stimulates immune response.
- Inapparent Infection – infection without symptoms.
4. Types of Reservoirs
- Human – carriers (Plasmodium, Salmonella).
- Animals – zoonoses (Rabies virus, Trypanosoma).
- Soil – Clostridium tetani, Toxoplasma gondii.
- Water – Vibrio cholerae.
Diseases
1. Principles of Establishment of Infection
- Tissue Damage – direct destruction of host cells (e.g., Entamoeba histolytica).
- Release of Toxins – exotoxins (Clostridium botulinum), endotoxins (E. coli).
- Obstruction of Vessels – filarial worms causing elephantiasis.
- Variation of Surface Antigens – Trypanosoma, Neisseria gonorrhoeae.
- Antigenic Mimicry – Streptococcus pyogenes M protein.
- Production of Enzymes – hyaluronidase, collagenase, coagulase, fibrinolysin.
- Destruction of Host Tissues – via cytotoxins or immune damage.
2. Classification of Infectious Diseases
A. Based on Organ System Involved:
- Gastrointestinal – Cholera, Salmonellosis, Dysentery.
- Respiratory – Pneumonia, Tuberculosis, Influenza.
- CNS – Meningitis, Encephalitis, Brain abscess.
- Cardiovascular – Endocarditis, Myocarditis, Pericarditis.
- Sepsis – bloodstream invasion, septicemia, septic shock.
- Skin/Soft tissue – Cellulitis, Necrotizing fasciitis.
- Genitourinary – UTIs, STIs.
B. Based on Microbiology:
- Bacterial – Gram + (Staphylococcus, Streptococcus), Gram - (E. coli, Salmonella), Mycobacteria.
- Fungal – Superficial (Ringworm), Subcutaneous (Sporotrichosis), Systemic (Histoplasmosis).
- Viral – DNA viruses (Herpesvirus, Hepatitis B), RNA viruses (HIV, Influenza).
- Parasitic – Protozoa (Plasmodium, Giardia), Helminths (Schistosoma, Taenia), Ectoparasites
(Lice, Mites).
- Prion – Scrapie, Creutzfeldt–Jakob disease, Mad cow disease.
3. Biological Properties of Pathogens
- Infectivity – ability to enter and multiply.
- Pathogenicity – ability to cause disease.
- Virulence – severity of disease.
- Immunogenicity – stimulates immune response.
- Inapparent Infection – infection without symptoms.
4. Types of Reservoirs
- Human – carriers (Plasmodium, Salmonella).
- Animals – zoonoses (Rabies virus, Trypanosoma).
- Soil – Clostridium tetani, Toxoplasma gondii.
- Water – Vibrio cholerae.
