Health and Hygiene

• WHO Definition of Health (1948): "Health is a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity."
• Why Not Merely Absence of Disease?
A person may not have any physical infection, virus, or fever, but if they are chronically anxious, depressed, emotionally distressed (poor mental health), or unable to form constructive relationships and adjust peacefully in community society (poor social health), they cannot be classified as a truly healthy human being.

• (a) Malaria:
• Pathogen: Parasitic protozoan Plasmodium (P. vivax, P. falciparum).
• Vector: Female Anopheles mosquito.
• Symptoms: Recurring high fever accompanied by severe chills, shivering, profuse sweating, and anemia.
• (b) Dengue:
• Pathogen: Dengue Virus (Flavivirus).
• Vector: Aedes aegypti mosquito (daytime biter with black-and-white striped legs).
• Symptoms: High fever, excruciating joint and muscle pain ("breakbone fever"), pain behind eyes, and dangerous drop in blood platelet count.

• Vaccine: A biological preparation containing dead, weakened (attenuated) pathogens, or their inactivated toxoids, that stimulates the immune system without causing the full-blown disease.
• Mechanism of Protection:
1. When inoculated, the body's immune system recognizes the foreign antigens on the vaccine particles.
2. B-lymphocytes synthesize specific Antibodies to neutralize them.
3. Crucially, the immune system creates long-lived Memory B-cells and Memory T-cells.
4. If the person is later exposed to the real, live pathogen in nature, these memory cells recognize it instantly and mount a massive, overwhelming antibody attack that destroys the pathogen before it can establish infection.

• Mechanism of Antibiotics: Antibiotics (like penicillin or amoxicillin) specifically target and destroy bacterial biochemical pathways—such as inhibiting bacterial peptidoglycan cell wall synthesis, disrupting bacterial ribosomes, or blocking bacterial DNA replication.
• Why Viruses are Immune:
Viruses do not possess cell walls, ribosomes, or their own independent metabolic machinery.
A virus is a non-cellular parasite made only of genetic material (DNA/RNA) inside a protein coat that hijacks the host cell's own human metabolic enzymes to replicate.
Antibiotics cannot attack host metabolic pathways without killing the human patient.

• (a) BCG: Bacillus Calmette-Guérin $\implies$ Prevents Tuberculosis (TB).
• (b) DPT (Triple Antigen): Diphtheria, Pertussis (Whooping Cough), and Tetanus.
• (c) MMR: Measles, Mumps, and Rubella (German Measles).
• (d) OPV: Oral Polio Vaccine $\implies$ Prevents Poliomyelitis (Infantile Paralysis).

1. Elimination of Breeding Habitats (Source Reduction): Discarding stagnant water from open drains, discarded automobile tires, flowerpots, and coolers. Mosquitoes require stagnant water to lay eggs and complete larval development.
   2. Biological Control: Introducing larvivorous fish such as Gambusia (Mosquito fish) or guppies into ponds and decorative water bodies; they voraciously feed on mosquito larvae and pupae.
   3. Chemical / Physical Control: Spraying kerosene or light oil on stagnant water surfaces (forms a thin film that suffocates mosquito larvae by blocking their breathing siphons); applying insect repellents and sleeping under insecticide-treated bed nets.

1. Physical Barrier (The Skin): The intact outer layer of skin is covered by keratinized, dead stratum corneum cells that form an impermeable, waterproof physical wall preventing microbial entry. Sebaceous sweat contains lactic acid and fatty acids that maintain a low pH ($5.5$) inhibiting bacterial colonization.
   2. Chemical / Physiological Barriers:
   • Hydrochloric Acid ($\text{HCl}$) in Stomach: Concentrated stomach acid (pH $1.5-2.0$) kills ingested bacteria and pathogens.
   • Lysozyme: An antibacterial enzyme present in tears, saliva, and nasal secretions that chemically dissolves bacterial cell walls.

• Chlorination: The process of adding a controlled dose of chlorine gas (or bleaching powder) to filtered drinking water to kill pathogenic microorganisms, bacteria, and amoebic cysts.
• Chemical Mechanism:
Chlorine reacts with water to form Hypochlorous acid ($\text{HOCl}$):

$$\mathbf{\text{Cl}_2 + \text{H}_2\text{O} \to \text{HCl} + \text{HOCl}}$$

Hypochlorous acid is a powerful germicide that penetrates bacterial cell walls and oxidizes essential metabolic enzymes, neutralizing pathogens and making water safe for consumption.