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SPI Biology · Microbiology and Disease

Diseases and Their Causes

An infectious disease is caused by a microbe (a virus, bacterium, protozoan or fungus) and often attacks one particular organ of the body.

All Microbiology and Disease notes

Why this matters

Two questions in the bank, both EASY: the microbe that causes malaria and the organ hepatitis attacks. The options in each are real microbes or real organs, so you need the exact pair, not a rough idea.

Concept 1 of 2: Diseases and the microbes that cause them

Every infectious disease has one kind of microbe behind it and a way of spreading. Learn the disease, its microbe group and how it spreads as one row.

Definition

  • Viruses: common cold, influenza, polio, measles, chickenpox, hepatitis, AIDS (HIV), dengue.
  • Bacteria: tuberculosis, typhoid, cholera, tetanus.
  • Protozoa: malaria (Plasmodium, spread by the female Anopheles mosquito), amoebic dysentery (Entamoeba), sleeping sickness (Trypanosoma).
  • Fungi: ringworm, athlete's foot.
  • Antibiotics work against bacteria, not viruses. Vaccines protect against many diseases before they strike.
DiseaseCaused byGroupSpread by
MalariaPlasmodiumProtozoanFemale Anopheles mosquito
Plasmodium causes malaria; the mosquito only carries it.
DengueDengue virusVirusAedes mosquito
Amoebic dysenteryEntamoebaProtozoanDirty water and food
Sleeping sicknessTrypanosomaProtozoanTsetse fly
TuberculosisMycobacteriumBacteriumAir
CholeraVibrio choleraeBacteriumDirty water
RingwormA fungusFungusTouch
Practice this conceptself-check · 4 quick reps

The same idea in a practice question:

Practice questionEasy

Example 1 · Microbiology and Disease · Diseases and Their Causes

Malaria is caused by

Naming the carrier as the cause

The female Anopheles mosquito carries malaria, but the cause is the protozoan Plasmodium. A question about the cause wants the microbe.

Ringworm is not a worm

Despite its name, ringworm is a fungal infection of the skin.

Concept 2 of 2: Diseases and the organ they attack

Many disease names carry a clue to the organ. 'Hepar' is Greek for the liver, so hepatitis is a disease of the liver; '-itis' means swelling or inflammation.

Definition

  • Hepatitis, jaundice: the liver.
  • Tuberculosis, pneumonia: the lungs.
  • Typhoid, cholera: the intestine.
  • Conjunctivitis: the eyes.
  • Polio: the nerves, leading to weak limbs. Meningitis: the covering of the brain.
  • Goitre (lack of iodine): the thyroid, in the neck. It is a deficiency disease, not an infection.
DiseaseOrgan attacked
HepatitisLiver
Hepar means liver.
JaundiceLiver
TuberculosisLungs
PneumoniaLungs
TyphoidIntestine
ConjunctivitisEyes
GoitreThyroid gland
Practice this conceptself-check · 3 quick reps

The same idea in a practice question:

Practice questionEasy

Example 2 · Microbiology and Disease · Diseases and Their Causes

Hepatitis is a disease of the

Jaundice of the kidney

Jaundice turns the skin and eyes yellow, but the organ at fault is the liver, like hepatitis.

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Reference tables (2)

Diseases and the microbes that cause them7 rows
DiseaseCaused byGroupSpread by
MalariaPlasmodiumProtozoanFemale Anopheles mosquito
Plasmodium causes malaria; the mosquito only carries it.
DengueDengue virusVirusAedes mosquito
Amoebic dysenteryEntamoebaProtozoanDirty water and food
Sleeping sicknessTrypanosomaProtozoanTsetse fly
TuberculosisMycobacteriumBacteriumAir
CholeraVibrio choleraeBacteriumDirty water
RingwormA fungusFungusTouch
Diseases and the organ they attack7 rows
DiseaseOrgan attacked
HepatitisLiver
Hepar means liver.
JaundiceLiver
TuberculosisLungs
PneumoniaLungs
TyphoidIntestine
ConjunctivitisEyes
GoitreThyroid gland

Watch out for (3)

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