communicable diseases

pathogen definition

organism that causes/transmits communicable disease

communicable definition

the effect of a transmissible pathogen

bacteria

• prokaryote

• reproduce rapidly

• release toxins and damage cells

• often live in vascular tissue in plants

• both gram positive and negative

• can be killed by antibiotics

fungi

• eukaryote

• most are multicellular (yeast is single celled)

• digestion is extracellular

• saprophytic or parasitic

• reproduce using spores

virus

• non living/require a host - DNA injected

• very small

• basic structure

protein coat

• can develop adaptations to host

• some are modified to treat disease by killing the pathogen

protoctista/protista

• eukaryotic

• varied organisms which don'y fit into other groups

• some are pathogenic

• protists that cause disease are parasitic

often need a vector

but can enter directly through polluted water

pathogens two modes of action

1. direct damage of tissue (viruses ad protists burst

2. production of toxins (leads to tissue damage)

tuberculosis

bacteria

bacterial meningitis

bacteria

ring rot

bacteria

HIV/AIDS

virus

influenza

virus

TMV

virus

black sigatoka

fungal

blight

fungal

ringworm (tinea corporis)

fungal

athletes foot

fungal

malaria

protist

direct contact

eg - ring worm

inoculation

break in the skin during sex

ingestion

contaminated food or drink

fomites

inanimate objects like bedding

eg - athletes foot

staphylococcus

droplet infections

when talking

eg - influenza

tuberculosis

vectors

transmit pathogens form one host to another

can be animals or water

factors affecting transmission (animals)

• overcrowding/living conditions

• poor nutrition

• climate

• poor health.immune system

• poor waste disposal

• lacked of trained health workers

direct transmission (plants)

contact between healthy and infected plants

eg - ring rot

TMV

soil contamination

infected plants leave pathogen/spores in soil

vectors

wind - eg: black sigatoka

water - rain droplets can spray pathogens onto other plants

animals - eg: malaria

humans - can transfer pathogens

factors affecting transmission (plants)

• drier conditions may reduce spread

• climate change (increased rainfall and wind promote dispersal)

• damp

warm conditions increase survival/spread of pathogens

• poor mineral nutrition

• overcrowding (increases contact)

primary defence

barriers which prevent the entry of pathogens

secondary defence

combat pathogens that have entered the body

skin

• physical barrier

• epidermal cells dry out

prevent entry

• sebum has antimicrobial fatty acid

• lower pH

lysozymes

• antimicrobial enzymes; break down bacterial cell walls

• found in blood

tears

mucous membranes

• line internal cavities (eg: airways

• made of goblet and epithelial cells

• mucus traps dirt and dust

• cillia waft mucas

expulsive reflexes

• eg: coughing

• when pathogen irritates airway air is explused

stomach acid

• hcl produced by stomach

ear wax

• physical blockage

• acidic

commensal

organisms/microbes that feed on the host while helping them

thromboplastin

triggers clotting (coagulation) when released from damaged cells lining blood vessels at injury site

serotonin

makes the smooth muscles in the walls of the blood vessels contract

clotting factors

any of the various plasma components involved in the clotting process

fibrin 3

acts as the glue

prothrombin

plasma protein; converted to thrombin in the clotting process

fibrinogen

soluble glycoprotein in plasma

platelets 1

acts as the plug

RBC and WBC role in clotting

support the clot

wound repair

• clot dries and forms scab

• new epidermal cells grow

• blood vessels regenerate

• collagen fibres deposited to strengthen new tissue

inflammation

• a localised response to pathogens or damage

• swelling in infected tissues

heat

• damaged mast cells release histamine and cytokines

histamines

• cause vasodilation

• make blood vessel walls more permeable; plasma forced out

more tissue fluid made

• raised temperature prevents pathogen reproduction

cytokines

• cell signalling compounds