UNIT 4 AOS 1 AGENTS OF DISEASE

DISEASE

any condition that interferes with how an organism, or any part of it, functions. can be classified as infectious or non-infectious.

INFECTIOUS DISEASE

a disorder caused by bacteria, viruses, fungi and other organisms, that can often be transmitted to other members of a population (eg. influenza)

NON-INFECTIOUS DISEASE

are caused by environmental, genetic or lifestyle factors and not by pathogens. they may be inherited disease (eg. cystic fibrosis), lifestyle disease (eg lung cancer), or nutritional disease (eg. anaemia).

CONTAGIOUS

refers to an infectious disease that is highly transmissible and spreads easily from person to person.

VIRULENCE

the degree to which a pathogen can cause disease

EPIDEMIC

many people in a given area become infected with a pathogen in a short amount of time

PANDEMIC

world wide (or several countries) spread of a disease form its point of origin accross a relatively short period of time (eg. COVID)

BACTERIA

unicellular prokaryotes that can be pathogenic and therefore carry disease.

FUNGI

a heterotrophic organism made up of one or many cells; has cell walls but is not a plant.

PROTIST

a unicellular eukaryotic organism.

PARASITE

an organism that obtains its nourishments from a host organism that is found in or on, which causes harm over time.

VIRUS

an obligate intracellular pathogen that can use the host cell’s machinery to replicate itself; usually consists of a nucleic acid surrounded by a protein coat.

VIROID

simpler form of a virus which lacks a capsid, and is essentially only short pieces of naked RNA that infect plants.

CAPSID

the protective protein shell that encloses the genetic material (DNA or RNA) of a virus. It acts as a barrier to prevent the viral genome from being damaged by physical, chemical, or enzymatic factors in the environment.

GRAM POSITIVE BACTERIA

are a classification of bacteria identified by their purple/violet colour after undergoing a Gram stain test. This characteristic colour is due to their cell walls, which contain a very thick layer of peptidoglycan that retains the crystal violet dye.

GRAM NEGATIVE

are a class of bacteria that do not retain the crystal violet stain in the Gram staining process, appearing pink or red under a microscope. They are characterized by a thin peptidoglycan cell wall sandwiched between an inner plasma membrane and a protective outer membrane.

AEROBES

organisms that require free oxygen to survive and efficiently generate energy (ATP) through aerobic cellular respiration.

FACULTATIVE ANAEROBES

is an organism that can generate ATP through aerobic cellular respiration when oxygen is present, but can switch to anaerobic respiration or fermentation when oxygen is absent.

OBLIGATE ANAEROBES

are organisms that cannot survive or grow in the presence of oxygen. Oxygen is highly toxic to them because they lack the specific enzymes required to neutralize harmful oxygen radicals. They rely entirely on anaerobic respiration or fermentation to produce ATP.

TRANSMISSION

the passing of a pathogen (infectious agent) from an infected host or reservoir to a new, susceptible host.

ENDOTOXIN

An endotoxin is a toxic lipopolysaccharide (LPS) that forms an integral part of the outer cell wall of Gram-negative bacteria. It is released into the host organism only when the bacterial cell ruptures or disintegrates (lysis), triggering a strong, systemic immune response.

EXOTOXIN

An exotoxin is a highly toxic, protein-based substance secreted by living pathogenic gram-positive and gram-negative bacteria into their surrounding environment (including host tissues). They are highly potent and specifically disrupt the normal cellular metabolism or destroy host cells, often leading to severe disease symptoms.

VECTORS

refers to an organism that transmits a pathogen between hosts.

ECTOPARASITE

a type of parasite that lives on the external surface of its host (such as on the skin, fur, or feathers) to obtain nutrients, causing harm or discomfort to the host while benefiting itself.

ENDOPARASITE

a type of parasite that lives inside the body of its host. These organisms obtain nutrients and shelter at the host's expense, frequently causing disease or harm to the host in a symbiotic relationship known as parasitism.

PRIONS

an infectious misfolded protein that can cause other unaffected prion proteins in the brain to take the affected and misfolded form, causing transmissible spongiform encephalopathies.

ACUTE

describes an immediate, short-term, or sudden response.

CHRONIC

refers to an ongoing, long-lasting disease, condition, or physiological state that persists over an extended period (typically longer than 6 months).

VIRION

virion is the metabolically inert particle capable of surviving outside a host. strictly refers to the virus when it is outside the host and acting as a transmissible, infectious unit.

ANTIBIOTICS

a naturally or synthetically produced compound that is toxic to bacteria.

SELF

refers to an organism's own cells and molecules, which carry specific Major Histocompatibility Complex (MHC) markers. The immune system identifies these markers as belonging to the body and leaves them alone, contrasting with foreign non-self antigens that it attacks.

NON-SELF

any molecule, cell, or particle that does not originate from an organism's own body. the immune system uses cell surface markers (like MHC proteins) to identify these as foreign and subsequently trigger an immune response to eliminate them.

ANTIGEN

a large molecule, usually a protein or polysaccharide, that generates an immune response.

MICROBIOTA

a community of micro-organisms, including fungi and bacteria, that live in or on another organism.