Infectious Disease
What you must understand
Infectious diseases are caused by pathogens: bacteria, viruses, fungi, protozoa and prions. Know how pathogens are transmitted (direct contact, droplets, vectors, contaminated food/water, blood) and how the body defends itself.
Understand the immune response: first-line defences (skin, mucous membranes, cilia, stomach acid), second-line defences (inflammation, phagocytosis, fever), and third-line specific immunity involving B cells (antibodies, humoral response) and T cells (cell-mediated response). Know the difference between active and passive immunity, and between natural and artificial immunity. Understand how vaccines work and the concept of herd immunity.
Know how diseases are treated and controlled: antibiotics act on bacteria, not viruses; antivirals target viral replication; hygiene, quarantine, vector control and vaccination reduce transmission. Understand the causes of emerging diseases and antibiotic resistance.
Traps in questions
- Antibiotics do not work against viruses.
- Vaccination gives active, artificial immunity; antibodies from mother to baby give passive, natural immunity.
- Antibodies are produced by B cells (plasma cells), not T cells.
- "Cure" and "prevention" are different - vaccines prevent, not cure.
Rule of thumb
For immunity questions, ask two questions: is the immunity active or passive (does the body make its own antibodies?), and is it natural or artificial (was it acquired through normal exposure or medical intervention)?
Worked example
A child receives a vaccine against measles. The vaccine contains antigens that stimulate antibody production, so the child develops active, artificial immunity and memory cells provide long-term protection.