Overview
This lecture covers the essential concepts of infectious diseases, focusing on key pathogens (bacteria, viruses, protoctists), their transmission, prevention, treatment, and the topic of antibiotics and antibiotic resistance for Cambridge International A Level Biology.
Infectious Diseases & Pathogens
- Infectious diseases are caused by bacteria, viruses, protoctists (protists), and fungi.
- Focus diseases: Tuberculosis (TB) and cholera (bacterial), HIV/AIDS (viral), malaria (protoctist).
- Pathogens cause harm by damaging tissue or releasing toxins.
Bacterial Diseases: Tuberculosis & Cholera
- Tuberculosis is caused by Mycobacterium tuberculosis and M. bovis, damaging lung tissue and suppressing immunity.
- TB spreads via air droplets; risks increase with close contact, weak immunity, overcrowded and poor living conditions.
- TB can be treated with antibiotics and prevented with vaccines.
- Control includes hygiene, quarantine, poverty reduction, improving healthcare access, and funding vaccination.
- Cholera is caused by Vibrio cholerae, spreading mainly through contaminated water/food.
- Causes severe diarrhea and dehydration; prevention focuses on clean water, sanitation, hygiene, education, and economic improvement.
Viral Diseases: HIV/AIDS
- Viruses are non-living, acellular, with RNA or DNA, a capsid, and sometimes an envelope from the host cell membrane.
- HIV targets and destroys helper T cells by binding to CD4 receptors and integrating its RNA via reverse transcriptase.
- AIDS develops when helper T cells are severely depleted, weakening the immune system.
- HIV/AIDs is transmitted via blood, sexual contact, and mother-to-child (perinatal).
- Prevention includes barrier contraception, safe blood handling, non-discriminatory education, and antiretroviral therapy access.
Protoctist Disease: Malaria
- Malaria is caused by Plasmodium, transmitted by mosquito vectors.
- Infects red blood cells, liver, and brain; causes severe symptoms with no vaccine or cure.
- Prevention focuses on vector control: insecticides, mosquito nets, antimalarial drugs, and public health education.
Antibiotics & Antibiotic Resistance
- Antibiotics inhibit bacteria by disrupting cell wall synthesis, damaging membranes, or blocking protein synthesis.
- Antibiotics do not work on viruses due to lack of cell walls and cellular machinery.
- Antibiotic resistance arises from random bacterial mutations, accelerated by overuse/misuse of antibiotics.
- Resistant bacteria (e.g., MRSA, Clostridium difficile) survive, reproduce, and spread resistance genes.
- Resistance makes infections harder to treat, increases costs, and threatens healthcare procedures.
- Prevention includes careful antibiotic prescription, patient education, and completing full courses.
Key Terms & Definitions
- Pathogen — a microorganism causing disease.
- Antibiotic — a substance that kills or inhibits bacteria.
- Antibiotic resistance — the ability of bacteria to survive despite antibiotic treatment.
- Vector — an organism (e.g., mosquito) that transmits pathogens.
- Capsid — protein coat surrounding viral genetic material.
- Reverse transcriptase — viral enzyme converting RNA to DNA in host cell.
- Helper T cell — immune cell targeted by HIV.
- MRSA — Methicillin-resistant Staphylococcus aureus, a multi-drug-resistant bacterium.
Action Items / Next Steps
- Review mechanisms of disease transmission and prevention for each pathogen.
- Understand antibiotic mechanisms and the causes of resistance.
- Complete any assigned readings or practice questions on infectious diseases and antibiotics.