Understanding Health, Disease, and Pathogen Transmission

Health and the Immune System

The World Health Organization (WHO) defines health as a state of complete physical, mental, and social well-being, not merely the absence of disease.

Components of Health

• Physical health: Body systems functioning properly.
• Mental health: Maintaining emotional and psychological balance.
• Social well-being: Fulfillment of basic human needs, including peace, food, education, a decent wage, and social justice.

Note: Any change in the body that results in a loss of health is considered a disease.

Key Medical Terminology

• Aetiology: The study of the causes of a disease.
• Symptoms: Subjective evidence of disease perceived by the patient (e.g., pain, fatigue, sadness, loss of appetite).
• Signs: Objective evidence of disease observed by a medical professional (e.g., fever, diarrhea, skin rash, vomiting).

Classification of Diseases

• Infectious: Caused by pathogens (microorganisms). A pathogen enters the body and reproduces, causing an infection.
• Non-infectious: Diseases not caused by pathogens.

Types of Pathogens

• Virus: Not considered true living things as they require a host cell to reproduce (e.g., flu, chickenpox).
• Bacteria: Unicellular prokaryotic organisms (e.g., tetanus, salmonella).
• Fungi: Multi- or unicellular eukaryotic organisms (e.g., athlete's foot).
• Protozoa: Unicellular eukaryotic organisms (e.g., malaria, sleeping sickness).

Transmission of Infectious Diseases

• Agent: The pathogen causing the disease (virus, bacteria, protozoa, or fungi).
• Reservoir: The environment where a pathogen lives and reproduces:
  • Environmental: Soil, water.
  • Animal or Human: A sick person or a carrier (someone who has the pathogen but shows no symptoms).
• Vector: An organism that carries and transmits the pathogen without being infected itself (e.g., mosquitoes, rats). Some organisms act as both vector and reservoir.
• Host: The organism that becomes infected after the pathogen bypasses physical body barriers.

Methods of Pathogen Transmission

• Direct contact: Person-to-person transmission via touching, kissing, or sexual contact.
• Indirect contact: Transmission via vehicles (objects, food) or vectors (animals).

Portals of Entry into Hosts

• Skin: Open wounds (e.g., tetanus, rabies, malaria).
• Digestive system: Contaminated food or water (e.g., cholera, salmonella).
• Respiratory system: Inhalation (e.g., flu, tuberculosis).
• Genital system: Sexual contact (e.g., AIDS, syphilis).

Epidemiological Classifications

• Endemic: Continually present in a specific region or population (e.g., malaria in tropical areas).
• Epidemic: Spreads rapidly and affects a large number of people simultaneously.
• Pandemic: Affects a very large geographical area or reaches all parts of the world (e.g., AIDS).