This document provides definitions and information about infectious diseases. It begins by defining infection as the invasion of a host's tissues by microorganisms that can cause subsequent injury and disease. An infectious disease is caused by the presence of microorganisms. Pathogenicity refers to a microbe's ability to cause disease, while virulence refers to the degree of pathogenicity. The document then discusses various microorganisms that can cause infections like viruses, bacteria, fungi, and parasites. It also covers the basic principles of infection transmission, prevention, and the nature of microorganisms. The stages of infectious disease are described along with factors that influence pathogenicity.

1. INFECTIOUS DISEASES
AETIOLOGY PATHOGENESIS &
CONSEQUENCES
Dr.T.V.Rao MD

2. in·fec·tion
dictionary means
• a. Invasion by and multiplication of
pathogenic microorganisms in a bodily
part or tissue, which may produce
subsequent tissue injury and progress
to overt disease through a variety of
cellular or toxic mechanisms.
• b. The pathological state resulting from
having been infected.
Dr.T.V.Rao MD 2

3. Definitions
• Disease and Infectious Disease
–Disease
•Any deviation from a condition of
good health and well-being
–Infectious Disease
A disease condition caused by the
presence or growth of infectious
microorganisms or parasites
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4. Definitions
• Pathogenicity and Virulence
– Pathogenicity
• The ability of a microbe to cause disease
• This term is often used to describe or compare
species
– Virulence
• The degree of pathogenicity in a microorganism
• This term is often used to describe or compare
strains within a species
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5. Principles of Infection
• Understanding the basic principles
of infection is essential for any
health care worker in any field of
health care.
1. Disease transmission
2. Prevention of disease
transmission

6. Nature of Microorganisms
• Microorganisms (microbes) are small,
living organisms that are not visible to the
naked eye.
• Pathogens (germs) are microorganisms
that cause disease.
• Non-pathogens are microorganisms that
do not cause disease; can be beneficial.

7. • Infection is the invasion
of a host organism's
bodily tissues by disease-
causing organisms, their
multiplication, and the
reaction of host tissues
to these organisms and
the toxins they produce.
Infections are caused by
microorganisms such as
viruses, prions, bacteria,
and Viroids, and larger
organisms like parasites
and fungi.
Infection means
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8. What is an Infection?
A harmful invasion and spread of foreign species, or
pathogen, in a host.
– VIRUS
• Small pox, measles, influenza, Ebola
– PRIONS
• Cow’s disease
– BACTERIA
• Tuberculosis, pneumonia, salmonella, anthrax
– FUNGUS
• Athlete’s foot, ring worm
– PROTISTS
• Malaria, toxoplasmosis, Algae

9. COURSE OF INFECTIOUS DISEASEs
• Exposure/Invasion of
Host
• Incubation -- period of
time between exposure
and onset of symptoms
-- e.g., interval between
HIV infection and
development of AIDS
can be as long as 10-15
years
• Host reaction
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10. Nature of Microorganisms
• Saprophytes
• Parasites
• Pathogens

11. Causative Agents effecting humans
u Bacteria
u Viruses
u Fungi
u Protozoa
u Helminths
u Prions
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12. • Streptococci (chains)
• Staphylococci (clusters)
• Diplococci (pairs)
• Micrococci (tiny)
• Flagellated forms (tails)
• Bacilli (rod-shaped)
• Vibrios
• Spirilla (spiral)
• Spirochetes (comma)
Types of Bacteria

13. • Fungi
– A plantlike organism that lives on
dead organic matter.
– Yeasts and molds can be pathogenic.
– Cause conditions such as ringworm,
athlete’s foot, yeast infections, and
thrush.
– Antibiotics do not kill fungi.
Antifungal medications are available,
but expensive and may cause liver
damage.
Types of Microorganisms

14. Types of Microorganisms
• Protozoa
– One-celled animal like organisms often
found in decayed materials and
contaminated water.
– Many contain flagella which allow them to
move freely.
– Cause diseases such as malaria, trichomonas,
and amebic dysentery.

15. • Viruses
– Smallest of all microorganisms – visible only using an
electron microscope.
– Cannot reproduce unless they are inside another
living cell.
– Spread by contact with blood and other body fluids.
– Difficult to destroy. Not affected by antibiotics.
– Associated with diseases such as the common cold,
chicken pox, herpes, hepatitis B, measles, warts,
polio, influenza, and AIDS.
Types of Microorganisms

16. Classification of Infections
• Primary Infection
Reinfection
• Secondary Infection,
• Focal infection,
• Cross infection,
• Nosocomial infections
• Iatrogenic infection

17. Source of Infections
• Endogenous
infection
•Exogenous
infections

18. Clinical Presentations
• In apparent infection
subclinical Infection
• In apparent infection,
• Atypical infections
• Latent infections

19. Source of Infection
• Humans from patient or carrier
• A healthy carrier
• Convalescent carrier
• Temporary carrier
• Contact carrier
• Paradoxical carrier

20. Source of Infections
• Animals
• Insects vectors
• Mechanical vector
• Biological vector
• Soil and water
• Food

21. MODES OF COMMUNICABLE DISEASE
TRANSMISSION
• Direct
Transmission
• Indirect
Transmission
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22. Modes of Transmission
• Direct contact
• Indirect contact
• Droplet
transmission
• Hands
• Vector-borne
• Nosocomial
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23. Transmission of Pathogens
•Direct contact
•Indirect contacts
•Air
•Objects
•Vectors

24. Modes of Transmission
Direct
transmission
Indirect transmission
Direct contact Airborne
Droplet spread Vehicle borne
Vector borne

25. DIRECT TRANSMISSION
• Immediate transfer of the disease agent by direct
contact between the infected and the susceptible
individuals
• Occurs through such acts as touching, biting,
kissing, sexual intercourse, or by direct projection
(droplet spread) by coughing or sneezing within a
distance of one meter
• Examples of diseases for which transmission is
usually direct are AIDS, syphilis, gonorrhea, and
the common cold
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26. INDIRECT TRANSMISSION
• May be one of three types: air-borne, vehicle-borne, or
vector-borne
• Air-borne transmission -- transmission of microbial
aerosols to a suitable port of entry, usually the respiratory
tract
– Microbial aerosols are suspensions of dust or droplet
nuclei made up wholly or in part by microorganisms --
may be suspended and infective for long periods of
time
– Examples of air-borne diseases include tuberculosis,
influenza, Histoplasmosis, and LegionellosisDr.T.V.Rao MD 26

27. INDIRECT TRANSMISSION (cont’d.)
• Vehicle-borne transmission -- contaminated
materials or objects (fomites) serve as vehicles,
nonliving objects by which communicable agents
are transferred to a susceptible host
–The agent may or may not have multiplied or
developed on the vehicle
–Examples of vehicles include toys,
handkerchiefs, soiled clothes, bedding, food
service utensils, and surgical instruments
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28. INDIRECT TRANSMISSION (cont’d.)
• Also considered vehicles are water, milk, food
(e.g., common vehicles), or biological products
such as blood, serum, plasma, organs and
tissues
• Almost any disease can be transmitted by
vehicles, including those for which the primary
mode of transmission is direct, such as
dysentery and hepatitis

29. Causing an Infection
• Endogenous – disease originates within the body.
Ex: metabolic disorders, congenital abnormalities,
tumors.
• Exogenous – disease originates outside the body. Ex:
chemical agents, electrical shock, trauma.
• Nosocomial – acquired by an individual in a health
care facility (workers to patient).
– Many are antibiotic resistant, life-threatening.
• Opportunistic – occur when the body’s defenses are
weak. Ex: pneumonia w/AIDs.

30. Signs & Symptoms of Infection
• Redness
• Swelling
• Tenderness
• Warmth
• Drainage
• Red streaks leading away from
wound
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31. Development of Infection:
Clinical Signs and Symptoms
• Local signs
– Inflammation
– Purulent exudate if bacterial infection; serous
exudate if viral
– Tissue necrosis
– Lymphadenopathy
– Respiratory effects
• Systemic signs
– Fever, fatigue, headache, nausea
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32. Generalized Stages of Infection
1. Entry of Pathogen
– Portal of Entry
2. Colonization
– Usually at the site of entry
3. Incubation Period
– Asymptomatic period
– Between the initial contact with the microbe
and the appearance of the first symptoms
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33. Generalized Stages of Infection
4. Prodromal Symptoms
– Initial Symptoms
5. Invasive period
– Increasing Severity of Symptoms
– Fever
– Inflammation and Swelling
– Tissue Damage
– Infection May Spread to Other Sites
– Acme (Fastigium)
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34. Factors predisposing pathogenicity
• Pathogenicity means
ability of the
microbe to produce
disease or tissue
injury
• Virulence
• May undergo
variation

35. Virulence and Pathogenicity
• Pathogenicity: capacity of microbes to cause
disease
• Virulence: degree of pathogenicity of specific
microbe
– Based on:
• Invasive qualities
• Toxic qualities
• Presence of pili or fimbriae for adhesion
• Ability to avoid host defenses (mutate)
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36. Virulence Factors and Toxins
• State of the Host
Immune System
• Number of
Pathogenic Cells
encountered by
the Host
–Infectious Dose
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37. Virulence Factors and Toxins
• Enzymatic Virulence Factors
– Examples:
• Coagulase (Staphylococcus aureus)
• Streptokinase (Streptococcus pyogenes)
• Hyaluronidase (Many pathogens)
• Collagenase (Many pathogens)
• Leukocidin (Many pathogens)
• Hemolysin (Many pathogens)
Dr.T.V.Rao MD 37

38. Virulence Factors and Toxins
• Adhesion Factors
– Examples:
• Protein A
(Staphylococcus
aureus)
• Protein M
(Streptococcus
pyogenes)
Dr.T.V.Rao MD 38

39. Virulence Factors
• Virulence factors help bacteria to (1)
invade the host, (2) cause disease, and
(3) evade host defences. The following
are types of virulence factors:
• Adherence Factors: Many pathogenic
bacteria colonize mucosal sites by using
pili (fimbriae) to adhere to cells.

40. Virulence Factors
• Invasion Factors: Surface components that
allow the bacterium to invade host cells can
be encoded on plasmids, but more often are
on the chromosome.
• Capsules: Many bacteria are surrounded by
capsules that protect them from opsonisation
and phagocytosis

41. Virulence Factors and Toxins
• Exotoxins
– A type of bacterial toxin with the following
properties:
• May be produced by either gram-positive or gram-
negative bacteria
• Is secreted by the bacteria
• The action of the exotoxin does not necessarily
require the presence of the bacteria in the host
• Most exotoxins are peptide or protein
• Most exotoxins are heat sensitive (exception:
enterotoxin of Staphylococcus aureus)
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42. Virulence Factors and Toxins
• Exotoxins (cont.)
– Classes of exotoxins: Neurotoxic, cytotoxic, or
enterotoxic exotoxins
• Neurotoxins: Interfere with proper synaptic
transmissions in neurons
• Cytotoxins: Inhibit specific cellular activities, such as
protein synthesis
• Enterotoxins: Interfere with water reabsorption in
the large intestine; irritate the lining of the
gastrointestinal tract
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43. Virulence Factors and Toxins
• Endotoxins
– A type of bacterial toxin having the following
properties:
• Produced only by gram-negative bacteria
• Endotoxins are a component of the gram-negative
cell wall
• The action of endotoxin requires the presence of
the bacteria in the host. The endotoxin may be
released from the cell wall as the cells die and
disintegrate
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44. Virulence Factors and Toxins
• Endotoxins (cont.)
• Endotoxin is composed
of Lipid A: Part of the
lipopolysaccharide
layer
• Mode of action:
Irritation/inflammation
of epithelium, GI
irritation,
capillary/blood vessel
inflammation,
hemorrhaging
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45. Endotoxins
• Endotoxins: The
lipopolysaccharide endotoxins on
Gram-negative bacteria cause
fever, changes in blood pressure,
inflammation, lethal shock, and
many other toxic events.

46. Mechanism of Endotoxin activity

47. Exotoxins
• Exotoxins: Exotoxins include
several types of protein toxins
and enzymes produced and/or
secreted from pathogenic
bacteria. Major categories
include cytotoxins, neurotoxins,
and enterotoxins.

48. Exotoxins
• Exotoxins, unlike the lipopolysaccharide
endotoxin, are protein toxins released from viable
bacteria. They form a class of poisons that is
among the most potent, per unit weight, of all
toxic substances. Most of the higher molecular-
sized exotoxin proteins are heat labile; however,
numerous low molecular-sized exotoxins are
heat-stable peptides. Unlike endotoxin, which is a
structural component of all Gram-negative cells,
exotoxins are produced by some members of
both Gram-positive and Gram-negative genera.

50. Exotoxins
• The functions of these exotoxins for the
bacteria are usually unknown, and the genes
for most can be deleted with no noticeable
effect on bacterial growth. In contrast to the
extensive systemic and immune-system effects
of endotoxin on the host, the site of action of
most exotoxins is more localized and is
confined to particular cell types or cell
receptors.

51. Exotoxins
• Tetanus toxin, for example, affects only intern
uncial neurons. In general, exotoxins are
excellent antigens that elicit specific
antibodies called antitoxins. Not all antibodies
to exotoxins are protective, but some react
with important binding sites or enzymatic
sites on the exotoxin, resulting in complete
inhibition of the toxic activity (i.e.,
neutralization).

52. Exotoxins
• Endotoxin is comprised of toxic
lipopolysaccharide components of the outer
membrane of Gram-negative bacteria (see Ch.
2). Endotoxin exerts profound biologic effects
on the host and may be lethal. Because it is
omnipresent in the environment, endotoxin
must be removed from all medical supplies
destined for injection or use during surgical
procedures.

53. Exotoxins
• The term endotoxin was coined in 1893 by
Pfeiffer to distinguish the class of toxic substances
released after lysis of bacteria from the toxic
substances (exotoxins) secreted by bacteria. Few,
if any, other microbial products have been as
extensively studied as bacterial endotoxins.
Perhaps it is appropriate that a molecule with
such important biologic effects on the host, and
one produced by so many bacterial pathogens,
should be the subject of intense investigation.

54. Other Factors
• Plasmids
• Bacteriophages
• Compatibility

55. Other Bacterial factors
• Coagulase
• Fibrinolysin
• Hyaluronidase

56. Bacterial Appendages
• Biofilms
• Free floating bacteria come in
contact with medical devices and
attach to them with pili

57. Infecting Dose
•Minimum infective
dose
•Minimal lethal dose

58. Types of Infectious diseases
•Bacteraemia
•Septicaemia
•Pyemia

59. Other types
•Endemic disease
•Epidemic disease
•Pandemic disease

60. Hospital acquired infections
• Infection which was
neither present nor
incubating at the time
of admission
• Includes infection which
only becomes apparent
after discharge from
hospital but which was
acquired during
hospitalisation (Rcn,
1995)
• Also called nosocomial
infection
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61. Basic steps in Prevention of Infection
• There are possible
treatment and
prevention to stop
the infection cycle.
This is through
adequate hygiene,
sanitary
environment
maintenance and
health education.
Dr.T.V.Rao MD 61

62. Antimicrobial agents In
Infection
• Anti-infective drugs such as antibiotics,
antiviral, antifungal and ant tubercular drugs
suppress infection. It can be administered by
mouth, topically or intravenously depending
on the infection extent and severity.
Sometimes, if drug resistance is known,
multiple drugs are used to stop drug
resistance and increase drug effectiveness.
Antibiotics only work for bacterial infection
and have no effect on viral ones.
Dr.T.V.Rao MD 62

63. INSPITE OF MANY ADVANCES THERE IS NO STEP GREATER
THAN HAND WASHING IN CONTROL OF INFECTIOUS
DISEASES

64. • Program Created by Dr.T.V.Rao MD for
Medical and Paramedical Professional for
Global education on Infectious Diseases
• Email
• doctortvrao@gmail.com