Topic 10) Infectious Disease (AS)

Topic 10: Infectious Disease

10.1 Infectious Diseases

🔹 Definition & General Understanding

• Infectious disease: A disease caused by a pathogen that can be transmitted from one host to another.

• Contrast with non-infectious diseases (e.g., genetic, autoimmune, or lifestyle-related).

🔹 Common Pathogens

• Bacteria

• Viruses

• Fungi

• Protoctists (protozoa)

🔹 Global Examples of Infectious Diseases

• Cholera – caused by Vibrio cholerae

• Malaria – caused by Plasmodium spp. (protoctist)

• Tuberculosis (TB) – caused by Mycobacterium tuberculosis

• HIV/AIDS – caused by Human Immunodeficiency Virus (HIV)

• Measles – caused by measles virus

• Smallpox – caused by Variola virus (eradicated)

🔹 Cholera

• Causative agent: Vibrio cholerae

• Mode of transmission: Ingestion of contaminated water or food

• Symptoms: Severe diarrhea, dehydration

• Control/prevention:

  • Safe drinking water

  • Improved sanitation

  • Oral rehydration therapy (ORT)

  • Vaccination

🔹 Malaria

• Causative agent: Plasmodium falciparum (most severe), P. vivax, etc.

• Vector: Female Anopheles mosquito (biological vector)

• Life cycle features:

  • Human host: liver and red blood cells

  • Mosquito vector: sexual reproduction

• Symptoms: Fever, chills, anemia, organ damage

• Control/prevention:

  • Insecticide-treated nets (ITNs)

  • Indoor residual spraying

  • Draining stagnant water

  • Antimalarial drugs (e.g., artemisinin)

🔹 Tuberculosis (TB)

• Causative agent: Mycobacterium tuberculosis

• Transmission: Airborne droplets (coughing, sneezing)

• Symptoms: Persistent cough, chest pain, blood in sputum, weight loss

• Latent vs Active TB

• Control/prevention:

  • BCG vaccination

  • Early detection and treatment

  • Antibiotics (e.g., isoniazid, rifampicin)

  • DOTS program (Directly Observed Therapy, Short-course)

🔹 HIV/AIDS

• Causative agent: HIV (Human Immunodeficiency Virus)

• Transmission:

  • Sexual contact

  • Blood-to-blood contact

  • From mother to child (during birth or breastfeeding)

• Effect on immune system:

  • Targets CD4+ T-helper cells

  • Reduces immunity → leads to AIDS

• Symptoms:

  • Early: flu-like symptoms

  • Later: opportunistic infections (e.g., TB, pneumonia)

• Control/prevention:

  • Safe sex practices

  • Blood screening

  • Antiretroviral therapy (ART)

  • Education and awareness programs

10.2 Antibiotics

🔹 Definition and Action

• Antibiotic: A substance produced by microorganisms that kills or inhibits the growth of bacteria.

• Types of action:

  • Bactericidal: Kills bacteria (e.g., penicillin)

  • Bacteriostatic: Inhibits bacterial growth (e.g., tetracycline)

🔹 Mechanism of Antibiotics

• Penicillin:

  • Inhibits synthesis of bacterial cell walls

  • Effective against Gram-positive bacteria

• Other mechanisms:

  • Inhibition of protein synthesis

  • Disruption of cell membrane

  • Inhibition of DNA/RNA synthesis

  • Inhibition of metabolic pathways (e.g., folic acid synthesis)

🔹 Limitations of Antibiotics

• Ineffective against viruses:

  • Viruses lack cell structures targeted by antibiotics

  • Viruses reproduce inside host cells

🔹 Antibiotic Resistance

• Development:

  • Natural selection: Resistant mutants survive and reproduce

  • Misuse and overuse of antibiotics (e.g., not completing treatment, using for viral infections)

• Mechanisms:

  • Enzyme production (e.g., β-lactamase breaks down penicillin)

  • Altered target sites

  • Increased efflux or decreased uptake

• Examples:

  • MRSA (Methicillin-resistant Staphylococcus aureus)

  • MDR-TB (Multi-drug resistant tuberculosis)

🔹 Controlling Resistance

• Prudent use of antibiotics

• Educating public and professionals

• Infection control in hospitals

• Development of new antibiotics

• Global surveillance and regulation