Biology Module 7: Infectious Disease

Disease

Any process or condition that adversely affects the normal functioning of a living thing or parts of a living thing

Infectious disease

Caused by an organism or infective agent and can be transmitted from one person to another

Pathogen

An infective agent

Non-infectious disease

Not caused by a pathogen and cannot be transmitted from one person to another

Vector

An agent that transmits pathogens

Prion

Infective proteins that are incorrectly folded and convert adjacent brain proteins to the misfolded ‘prion’ form

Virus

Non-cellular pathogens that contain a nucleic acid enclosed by a capsid

Capsid

A protein coat that encloses nucleic acid

Fomites

Non-living objects that carry pathogens

Bacteria

Unicellular prokaryotes that are cellular pathogens

Protists/protozoa

Unicellular eukaryotes that are microscopic animal-like cells

Fungi

Eukaryotes that vary widely in size and have a cell wall made up of chitin

Macroscopic parasites

Multicellular eukaryotic pathogens

Endoparasites

Parasites that live inside the host

Ectoparasites

Parasites that live outside the body

Helminths

Worm-like endoparasites (e.g. tapeworm)

Incidence

The number of newly diagnosed cases of a disease

Prevalence

The total number of live cases of a disease or proportion of a population that have a disease

Mortality

The number of deaths or proportion of a population that die from a disease

Endemic level of disease

The baseline rate (incidence of prevalence) of a specific disease in a certain population

Epidemic

A widespread increase in the prevalence of a particular disease (sometimes also called an “outbreak”) above the endemic rate.

Pandemic

An epidemic which has spread across multiple countries or continents

Germ theory

The scientifically accepted principle that microscopic organisms—pathogens like bacteria, viruses, fungi, and protists—are the root cause of many diseases

Miasma theory

Argued that diseases like cholera and the plague were caused by "bad air" (miasma) or toxic vapours emanating from rotting organic matter

Louis Pasteur’s Swan-neck Flask Experiments

Definitively disproved the theory of spontaneous generation by showing that microorganisms grow in broth only when exposed to contaminants, not spontaneously from air

Louis Pasteur

French chemist and microbiologist who revolutionized medicine and industry by establishing the germ theory of disease and inventing pasteurisation

Pasteurisation

A food safety process, developed by Louis Pasteur, that uses mild heat to kill pathogenic microorganisms and extend the shelf life of products

Robert Koch

A pioneering German physician and microbiologist, widely regarded as a founder of modern bacteriology. He established the germ theory of disease by proving specific bacteria cause diseases

Koch’s postulates

Four established criteria formulated by Robert Koch to identify the causative agent of a specific infectious disease

Endemic

one constantly present at a baseline level within a specific geographic area or population group

Internal parasites

organisms that live inside the human body—primarily the gut—to survive, often causing symptoms like abdominal pain, diarrhea, and fatigue

Anthrax

a serious disease usually caused by Bacillus anthracis bacteria. The bacteria are found naturally in soil around the world and often affect livestock and wild animals

Australian bat lyssavirus (ABLV)

A rare but fatal virus found in Australian bats that is closely related to the classical rabies virus. It affects the central nervous system and can be transmitted to humans through the saliva of an infected bat, usually via a bite or scratch

Flystrike

A serious, often fatal condition where blowflies lay eggs in wet, soiled wool or open wounds on sheep, hatching into maggots that eat the skin and tissue

Citrus canker

A highly contagious, bacterial disease caused by Xanthomonas citri subsp. citri that affects citrus trees, causing leaves, fruit, and twigs to develop scabby, crater-like lesions

Wheat rusts

A major fungal disease caused by Puccinia species, specifically leaf, stem, and stripe rust

Potato moth

A highly destructive pest of potato crops, tomatoes, tobacco, and eggplant

Karnal bunt of wheat

A fungal disease caused by Tilletia indica that infects wheat, durum wheat, and triticale during flowering

Agriculture

The science and practise of cultivating land for the purposes of growing plant crops or raising animals for food or other products such as wool or leather.

Transmission

The mechanism by which a pathogen spreads disease from one individual to another

Watermarking

A symptom of plant viruses - faint, nearly invisible swirls and squiggles in the green colour of the leaf

Vein banding

A symptom of plant viruses - yellow veins and green leaf

Stomata

Openings in the leaves (for transpiration)

Apoptosis

Programmed cell death

Antigen

Any foreign molecule that your body recognises as ‘non-self’ and that triggers an immune response

Innate Immune Response

Made of defenses against infection that can be activated immediately

1st line of defence

Prevent entry of pathogens into the body (physical and chemical barriers)

2nd line of the defence

Non-specific internal immune responses that help limit the spread of pathogen throughout the body if the 1st line of defence is breached

Adaptive immune response/3rd line of defence

Carra highly specific, acquired defense mechanism that targets particular pathogens, providing long-lasting immunity through immunological memory

Cilia

Tiny finger-like projections that line the trachea and bronchi

Lysosomes

Present in tears and saliva; chemicals that destroy the cell wall of pathogens

Phagocytosis

Involves the process of phagocytes engulfing and absorbing foreign matter and digesting it

Phagocyte

A specialised white blood cell that can engulf foreign matter

Neutrophil

A type of phagocyte; the most abundant white blood cell in the body; particularly toxic to bacteria and fungi; self-destruct following phagocytosis, forming pus

Macrophage

A type of phagocyte and antigen-presenting cell; can destroy pathogens and cancer cells

Cytokines

Proteins released by macrophages to signal and recruit other cells to an area with pathogens

Dendritic cells

Antigen-presenting cells that are located in tissues; can identify threats, act as messengers and act as a bridge between innate and adaptive immune system

Natural killer cell

A white blood cell that kills tumour and virus-infected cells; uses enzymes to trigger apoptosis

Basophil

A white blood cell that targets multicellular parasites and releases histamines

Histamines

Chemicals that trigger the inflammation response (dilation and permeability), also responsible for some allergic reactions

Eosinophil

A type of white blood cell that targets bacteria and multicellular parasites

Inflammation

A chemical response that occurs at the site of infection and plays a major role in wound healing

Prostaglandins

Chemicals released by infected/damaged cells to trigger inflammatory response (fever and pain)

Lymph system

A network of vessels, tissues, and organs that transports lymph fluid, removes waste, and houses white blood cells to protect against infections

Lymph nodes

small, bean-shaped immune system organs that act as filtering stations, trapping pathogens, debris, and cancer cells from lymph fluid

Complement proteins

Assist other defence mechanisms (tagging pathogens, attracting phagocytes, puncturing pathogen membranes)

Pyrogens

A chemical released by phagocytes that causes part of the brain that regulates body temperature to increase the set point (fever)

Granuloma/cyst formation

a small, non-cancerous cluster of immune cells (macrophages) that forms, often in the lungs, skin, or liver, to isolate harmful substances, infections, or foreign bodies

Lymphocyte

a vital type of white blood cell produced in the bone marrow and key to the adaptive immune system

Microflora

Natural harmless microbes that live in the body and inhibit the growth/entry of pathogens

Antigen-presenting cell

specialized immune cells that detect, engulf, and break down pathogens, displaying fragments (antigens) on their surface to T-cells