Introduction to Microbiology 3

Introduction to Microbiology 3

Infection/ Immunology

An infectious disease is a change in health in the host that is not properly balanced or able to carry on functioning as normal with the pathogen (disease causing agent)affecting it

Course of Infection

  1. Incubation period (rarely any signs or symptoms)
  • After entering the body, the pathogen needs to establish itself and multiply
  • This is the time between the exposure and the onset of symptoms
  1. Early Stage (symptoms and signs are mild) (not every disease has this stage, and may start suddenly)
  • Symptoms are showing
  • Signals the beginning of the disease
  • Non specific symptoms:
    • Headaches
    • Nausea
    • Lethargy and a general feeling of unwellness
      At this stage the body’s immune system may over come it.
  1. Acute or Invasive Stage (Identifiable from symptoms)
  • Pathogen invades and damages the tissue of host
  • Fever, chills usually occurs at this stage
  • Peak is reached and the symptoms will subside in some cases
  1. Death or Immune Response Kicks in or Treatment = Recovery
  • Covalence: the body repairs itself and regains strength, if not enough time is allowed, the body will stay weak and susceptible

Acute: not small, symptoms appear and the disease runs its course quickly

Fulminating: symptoms appear suddenly and disease runs through quickly = often fatal result

Chronic: disease progresses slowly and continues for a long period of time

Latent: the pathogen will lie dormant and strike at a later time

Subclinical: Infection produces a immune response without identifiable symptoms

Types Of Infections

Opportunistic: doesn’t cause disease in a healthy host, but when the immue system is down or compromised, it will strike.

Localised: only in one part of the body

Synthetic: pathogen affects more than one organ

Mixed: disease is due to the effect of more than one pathogen

Primary: the first sign of infection in a healthy host

Secondary: develops when immune system is down by the primary infection

Super-Infection: occurs from the overload of opportunistic  microbes after the distruction of normal flora.

Socioeconomic factor eg hygiene

Nosocial or hospital acquired – surgical wound infection or respiratory infection or UTI


Zoonotic eg exposure to animals

Signs and Symptoms

Fever Inflammation Pain or tenderness Fatigue
Swelling Warmth Skin Rashes
Redness Headache Nausea

Body’s Defences

First – non specific Physical and chemical defences (Skin and mucous membrane)
Second – non specific Complement, neutrophils, macrophage and inflammation
Third –specific Anti-bodies, B and T cell responses, lymphocytes

Inflammation: the redness, swelling, pain, heat and pus, bring in phagocytes (eat the baddies/ foreign microbes), wall off invaders.



v  Exposure leads to  immediate maximum response

v  Cell mediated and humoral components

v  No immunological memory

v  Found in nearly all forms of life

v  Functions as the 2nd line of Defence


v  Lag time between exposure and maximum response

v  Sell mediated and humoral companents

v  Exposure leads to immunological memory

v  Found only in vertbrates


v  Involves T and B lymohocytes, the T and B cell recognition of antigen turns on the immune response

v  Memory generated to allow 2nd greater response

Affect the Resistance Of Host:

v  Age – children or elderly

v  Genetics

v  Immune deficiencies

v  Malnutrition

v  Chronic disease

v  Sever stress – emotional and physical

v  Damaged primary defence (cuts or burns)

v  Poor inflammatory response


Severity of the affect the microbe is capable of doing

v  Invasive Qualities -small size (virus)

v  Adherance factors – pili and fimbrE

v  Toxic Qualites – production of toxins and destructive enzymes

v  Immune Evasion – mutation and change of antigen, bacteria capsule

v  Resistance to treatment – superbugs

v  Rate of replication



Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s