infection - Immunology notes

2.  A disease or disorder caused by infectious agent such as bacteria,
viruses, protozoans of fungus – called infectious disease
 It occurs when an pathogen enters the body and begins to reproduce,
may lead to disease – called infection
 Most of the infectious agent that cause disease are microscopic in size
and these are called microbes
 Mode of action
 Production of poison – ie toxin, enzymes, protein derivatives
 Direct invasion
 Triggering

3. Phases of infectious disease
 Incubation period
The time between infection and appearance of sign and symptoms
 Prodromal phase
Mild, non specific symptoms, that signal onset of some disease
Ex: Cough, sneeze, mild irritation, rashes, pimples etc..,
 Clinical phase
A person experiences typical signs and symptoms of disease
Ex: Fever, cold, inflammation, diarrhea, severe pain etc..,
 Decline phase
 Subsidence of symptoms
 Recovery phase
 Symptoms disappeared, tissues heals, body regain strength

4. Classification of Infectious disease
I) By Duration
Acute: signs and symptoms formed quickly, persist for short time,
may be week to months
ex: cold, fever, swelling
Chronic: Slow start, persist for long time, may be one year
ex: diabetes, heart diseases, cancer etc.,
Latent: A latent infection is an infection that is hidden, inactive, or dormant.
As opposed to active infections, where a virus or bacterium is
actively replicating and potentially causing symptoms
ex: Chicken pox, HIV, hepatitis,

5. 2. By location
Local: infection occurs in the specific area of body
ex: redness eye, tooth ache, swelling in hand, papules on face
Systemic: Systemic means affecting the entire body, rather than a
single organ or body part.
ex: high blood pressure, flu, corona, HIV, many fungal infection.
3. By timing
Primary: Initial infection in a healthy persons
Ex: boils, impetigo etc.,
Secondary: It occurs in a weakened persons by a primary infection
Ex: pneumonia, typhoid, AIDS

6. Examples of infectious disease
 bacterial infection
 viral infection
 fungal infection
 protozoan infection
Transmission of infectious disease
 Air
 Water
 Body fluids
 Contaminated objects
 Vectors etc.,

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