Flashcards · 9700 · AS Topic 10

Infectious diseases (AS Level) flashcards

11 cards on AS Topic 10, subtopics 10.1 to 10.2. Pick a subtopic or study them all.

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Pathogen and infectious disease: Pathogen: an organism or virus that causes disease. Infectious disease: a disease caused by a pathogen that is transmissible from one host to another.
Cholera: pathogen and transmission: Vibrio cholerae, a bacterium. Faecal–oral: water or food contaminated with faeces from an infected person. A toxin makes chloride ions and water leave the gut lining, causing severe watery diarrhoea.
Malaria: pathogen and transmission: Plasmodium (P. falciparum, P. malariae, P. ovale, P. vivax), a protoctist. Vector: the female Anopheles mosquito during a blood meal; also blood transfusion, shared needles and across the placenta.
TB: pathogens and transmission: Mycobacterium tuberculosis: airborne droplets from coughs and sneezes. Mycobacterium bovis: unpasteurised milk or undercooked meat from infected cattle.
HIV/AIDS: pathogen, transmission and effect: Human immunodeficiency virus. Spread in body fluids: unprotected sex, shared needles, unscreened blood, mother to child. It destroys T-helper lymphocytes, so the immune system fails (AIDS) and opportunistic infections take hold.
Why is malaria hard to control?: Mosquitoes become resistant to insecticides and Plasmodium to drugs; the parasite hides inside liver and red blood cells; there are social (nets not used) and economic (cost of nets, sprays and drugs) limits.

Antibiotic: A substance that kills bacteria or stops their growth, with little or no harm to human cells.
How does penicillin kill bacteria?: It inhibits the enzymes (transpeptidases) that form peptide cross-links in the peptidoglycan wall of growing bacteria. The wall weakens, water enters by osmosis and the cell bursts (osmotic lysis).
Why do antibiotics not affect viruses?: Viruses have no peptidoglycan cell wall, no ribosomes and no metabolism of their own; they replicate inside host cells using host enzymes, so there is nothing to target.
How does antibiotic resistance spread in a bacterial population?: A random mutation gives a resistance allele. The antibiotic kills susceptible bacteria (selection pressure); resistant ones survive and divide. The allele passes to offspring (vertical) and on plasmids to other bacteria (horizontal).
Ways to reduce the impact of antibiotic resistance: Prescribe only when needed (never for viral infections); use narrow-spectrum drugs after testing; complete the course; rotate antibiotics; reduce use in farming; better hospital hygiene.