Infection occurs when a microbe lodges and multiplies in the tissues of a host. Ranges of relationships between microbes and hosts include saprophytes, parasites, and commensals. Several factors predispose to microbial pathogenicity, including adhesion, invasiveness, and toxigenicity. Infections can be classified as acute or chronic, primary or secondary, localized or systemic, and clinical or subclinical. Six links must be present for an infection to spread: a portal of entry, a susceptible host, a causative agent, a reservoir, a portal of exit, and a mode of transmission. Microbes can be transmitted through various methods including direct or indirect contact, inhalation, ingestion

1. Infection
DEEPA BABIN
ASST PROF, MICROBIOLOGY, TMC

2. Infection
Infection -The lodgement and
multiplication of a microbe in or on
the tissues of a host.
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

3. Range of relationships
Saprophytes – Free living microbes
subsisting on dead or decaying organic
matter.
Parasites – Microbes establishing and
multiplying themselves in hosts.
Commensals – Microbes living in complete
harmony with host without causing any harm to
them.
Pathogens Microbes capable of causing disease
in host.

4. Predisposing Factors to Microbial
Pathogenicity
–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
• Exaltation-Enhancement of virulence
• Attenuation-Reduction of virulence

5. Classification of infection
• Acute infection vs. Chronic infection
–Acute Infection
•An infection characterized by sudden
onset, rapid progression, and often
with severe symptoms
–Chronic Infection
•An infection characterized by delayed
onset and slow progression

6. Primary vs. Secondary infection
–Primary Infection
•Intial infection that develops in an
healthy individual
– Secondary Infection
•An infection that develops in an
individual who is already infected with a
different pathogen
-Reinfection
Subsequent infection with the same
pathogen in same host

7. Localized vs. Systemic infection
–Localized Infection (focal)
•An infection that is restricted to a
specific location or region within the
body of the host
–Systemic Infection
•An infection that has spread to several
regions or areas in the body of the host

8. Clinical vs. subclinical infection
–Clinical Infection
• An infection with obvious observable or
detectable symptoms
–Subclinical Infection
• An infection with few or no obvious
symptoms
Atypical infection
• Typical clinical features of particular
infection is not present

9. ENDO vs EXO
• Endogenous – disease originates
within the body. Ex: metabolic
disorders, congenital abnormalities,
tumors.
• Exogenous – disease originates
outside the body. Ex: chemical
agents, electrical shock, trauma.

10. Nosocomial infection-
–Cross infection-Already suffering from disease
and acquire new disease from another host or
another external sources
–Nosocomial infection-
–Hospital acquired infection
–Iatrogenic infection-
• Physician induced infection during
therapeutic or investigative procedures

11. Latent & Opportunistic infection
–Latent infection-
• After following an infection the pathogen remain in
tissues in a hidden or latent form which produce
clinical disease when the host resistance is lowered.
• Opportunistic infection
–An infection caused by microorganisms that are
commonly found in the host’s environment. This
term is often used to refer to infections caused
by organisms in the normal flora

12. Causing an Infection
• In order for disease to occur and spread from
one individual to another, certain conditions
must be met.
• If any one condition is not met, the
transmission of the disease will not happen.
• Pathogens are everywhere and preventing
their transmission is a continuous process.

14. Introduction of a flora

15. •Portal of Entry
• Susceptible Host
• Causative Agent
• Reservoir
• Portal of Exit
• Mode of Transmission
6Links to the Chain of Infection

16. SOURCES OF INFECTION
Human Beings • Animals
• Patients
• Carriers
Healthy
Convalescent
Temporary
Chronic
Contact
Paradoxical
• Zoonosis
• Reservoir
Insects
• Mechanical
• Biological
Soil & Water
Food,Formites

17. Carriers
• Carrier/Human cases
–An individual who carries an infectious
agent without manifesting symptoms, yet
who can transmit the agent to another
individual- Healthy carrier
–Convalescent carrier-Individual who
recovered from infectious disease but
continous to harbour the pathogen

18. CARRIERS
• Temporary –harbor the pathogen for
short time(days,weeks)
• Chronic - harbor the pathogen for long
time(months years,life)
• Contact –Acquires the pathogen from a
patient
• Paradoxical- Acquires the pathogen from
another carrier

19. •Animal Vectors
•An animal (nonhuman) that can transmit an
infectious agent to humans
•Two types: mechanical and biological
–Biological animal vectors: The infectious agent
must incubate in the animal host as part of the
agent’s developmental cycle; eg, the transmission of
malaria by infected mosquitoes
–Mechanical animal vectors: The infectious agent is
physically transmitted by the animal vector, but the
agent does not incubate or grow in the animal; eg,
the transmission of bacteria sticking to the feet of
flies

20. METHODS OF TRANSMISSION
OF INFECTION
• Contact-Direct/ Indirect-5Fs
• Congenital-
• Inhalation
• Ingestion
• Inoculation
• Insects
• Iatrogenic
• Lab Acquired

23. Factors predisposing to Microbial Pathogenicity
1.Adhesion –Adhesins
2. Invasiveness
3.Toxigenicity-Exotoxins ,Endotoxins
4.Plasmids
5. Enzyme production IgA ,proteases
6.Bacteriophages
7.Communicability
8. Bacterial appendages
9.Infecting dose-MID AND MLD

24. Exotoxins Vs Endotoxins
• Protein
• 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 Ab
• Both G + &G –
• Eg:Botulinum,Tetanus,Diphth
eria
• LipoPolysaccharide
• Heat Stable
• Part of cell wall. No
diffusion
• Obtained only by cell lysis
• No Enzymatic action
• Effect nonspecific
• Not specific
• Active in large doses
• Weakly antigenic
• Antibody does not
• Gram negative

25. 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

26. Prodromal Symptoms
–Initial Symptoms
5. Invasive period
–Increasing Severity of Symptoms
–Fever
–Inflammation and Swelling
–Tissue Damage
–Infection May Spread to Other Sites

27. Epidemiological terms
• ENDEMIC-Disease constantly present in
particular area
• EPIDEMIC-spreads rapidly, involves
many persons in an area at a time
• Eg-meningococcal meningitis, Influenza
• PANDEMIC-spreads many areas in
world involves large no with in short
period-Cholera,Enterovirus

28. DEFINITIONS
Epidemiology
The study of the transmission of disease
Communicable Disease
–A disease that can be transmitted from one
individual to another
• Contagious Disease
• A communicable disease that is easily spread from
one individual to another
• Non communicable Disease -A disease that is not
transmitted from one individual to another

29. TYPES OF INFECTIOUS DISEASES
• Bacteremia
• Common occurrence
while brushing, chewing
Septicemia
•Circulation,multiplication
, formation of toxins
with high swinging fever
• Pyemia –
• Septicemia by pyogenic
organisms. Produces
multiple abscesses in
internal organs.