BIOLOGY

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DISEASE DEFINITION

Any condition that alters the wellbeing of an organism or any part of its functions, causing physiological or psychological dysfunction. Diseases can be caused by pathogens, genetic factors, or environmental influences.

HEALTH

The state of complete physical, mental, and social well-being, not merely the absence of disease or infirmity.

INFECTIOUS DISEASES

Diseases caused by pathogenic microorganisms such as bacteria, viruses, fungi, or parasites that can spread directly or indirectly between individuals.

INFECTED ORGANISM

Host/host to a virus

NON-INFECTIOUS DISEASE

NOT caused by pathogens and can’t be transmitted between organisms

Non-infectious disease categories

• ENVIRONMENTAL - external conditions (e.g. pollution)

• GENETIC - Inherited from genes

• LIFESTYLES - Daily behaviours cause the disease (e.g. diet, exercise)

PATHOGENS

Microorganisms that act as agents for disease

TYPES OF PATHOGENS

• Bacteria

• Viruses

• Prions

• Fungi

• Protists

• Parasites

BACTERIA

Prokaryotes (single-celled organisms) with simple internal structure that lacks nucleus

VIRUS

Consists of nucleic acid molecules in a protein coat that can multiply with living cells of host.

PRIONS

Abnormal form of normally harmless protein found in brain - Abnormally harmful proteins from brain.

FUNGI

Eukaryotic (complex-celled organisms - nucleus + membrane) most of time. Pathogenic fungi are unicellular + affect host’s skin

PROTISTS

Eukaryotic & includes protozoans which have elaborate life cycles

PARASITES

Multicellular eukaryotic organism that lives in or on host organisms by feeding off their nutrients

INFECTIOUS DISEASE RISK FACTORS

• HIGH EXPOSURE RATES - more microbes exposed to vulnerable = increased chance of infection

• WEAK IMMUNE SYSTEM - body can’t defend against pathogens

• POOR HYGIENE - Pathogens (bacteria) can transfer easily to surfaces new host touches (contaminated surfaces)

• LITTLE VACCINATIONS - No vaccines = less prepare/no defence

DIRECT CONTACT

Infectious disease from host can transmit it through physical contact with susceptible organisms

MODES OF TRANSMISSION: Direct Contact

• PHYSICAL CONTACT - touching, sexual intercourse, shaking hands

• DROPLET SPREAD (airborne particles) - breathing, talking, coughing, sneezing

INDIRECT CONTACT

Spread of infectious agents from one person to another without physically touching

INTERMEDIATES OF INDIRECT CONTACT

• Air (particles in air for longer time)

• Water

• Food

• Contaminated objects

• Animal vectors (e.g. mosquito blood)

PATHOGEN RESERVOIRS

Individuals (carriers) who are not affected by symptoms of a disease, but may spread pathogens to others

PATHOGEN PERSISTENCE

Ability for pathogens to remain/live in host for a long time

HERD IMMUNITY

Resistance