4.1.1. communicable disease, defence and the immune system

define disease

a disorder of structure or function in a human, animal or plant that produces specific symptoms or that affects a specific location and is not simply a direct result of physical injury

define a communicable disease

a disease caused by a pathogen that can be transmitted directly or indirectly from one individual in a population to another

define means of transmission

movement of pathogens from a reservoir to a susceptible host

define susceptible host

individual/member of population at risk of becoming infected by a disease

define reservoir

any person, animal, plant, soil or substance in which a pathogen normally lives and multiplies and serves as a source from which other individuals can be infected

how can reservoirs (sources) for diseases be minimised

personal hygiene, isolation, quarantine

how can the means of transmission of a disease be minimised

personal hygiene, environmental sanitation: air, food, water, waste, insects

how can a susceptible person of a disease be minimised

immunization, personal hygiene

define a pathogen

any agent causing a communicable disease, usually a microorganism

what is a parasite

a multicellular organism that lives on or in a host

what are the main types of pathogen

protozoa, fungi, bacteria, virus

what is the size of a protozoa

1-150 um

what kingdom is a protozoa in

protoctista

what type of cell is a protozoa

unicellular eukaryote

what is the size of fungi

2-30 um in diameter, grow as hyphae which can be several cm long

what kingdom are fungi in

fungi

what cell type are fungi

eukaryotic, unicellular or multicellular organisms

what size are bacteria

0.5-50 um in length

what kingdom are bacteria in

prokaryote

what type of cells are bacteria

unicellular prokaryote

what length are viruses

20400 nm

what kingdom are viruses in

not a cell so often outside of classification of living organisms- doesn’t belong to a kingdom

what are the features of a virus

an infective agent containing only:

• genetic material: a single strand of DNA or RNA in a

• protein coat

only able to multiply within the living cells of a host

define transmission of disease

the transfer of a pathogen from a reservoir to a susceptible host

what are categories of direct contact for transmission of disease

direct physical contact, transplacental, inoculation

examples of direct physical contact as a form of transmission of disease

skin-skin e.g. shaking hands, sex, kissing, plant-plant, faeces→hand→mouth

description of transplacental transmission of disease

mother to foetus e.g. HIV

description and examples of inoculation as a transmission of disease

from syringe into blood e.g. HIV, hepatitis. blood transfusions, sharing needles

categories of indirect contact as transmission of disease

vehicle-borne, water-borne, air-borne, vector-borne

examples of vehicle-borne transmission of disease

bedding, clothing, utensils, in animals: athletes foot in socks, in plants: farm machinery

examples of water-borne transmission of disease

in animals: diarrhoeal diseases carried in water, in plants: rain-drop splashes

examples of air-borne transmission of disease

in animals: droplets of saliva/mucus released by coughing/sneezing/talking carry pathogens e.g. influenza, TB, in plants: spores of bacteria, fungi and viruses carried by wind and land on leaves

examples of vector-borne transmission of disease

in animals: mosquitos carry malarial parasite plasmodium, when bits it injects saliva into blood of susceptible host, in plants: insects can act as vectors when they feed from plant sap in phloem e.g. aphids can transmit viruses

define vector

an organism that carries and transmits pathogens between individuals of a different species

examples of animal diseases

HIV/AIDS, influenza, tuberculosis, malaria, athletes foot

what type of pathogen in HIV/AIDS

virus

what are the means of transmission of HIV/AIDS

passed on through bodily fluids e.g. unprotected sex, sharing needles

what are the symptoms of HIV/AIDS

fevers, tiredness, headaches, destroys immune system so vulnerable to other infects e.g. TB, blood tests positive

what type of pathogen is influenza

virus

means of transmission of influenza

airborne via droplets when coughing or sneezing

symptoms of influenza

cough, fever, sore throat, runny nose, headache

what type of pathogen is tuberculosis

bacteria

means of transmission of tuberculosis

airborne via droplets

symptoms of tuberculosis

chronic cough with blood, fever, night sweats weight loss, suppresses immune system so more vulnerable to other diseases e.g. HIV/AIDS

what type of pathogen is malaria

protoctista

means of transmission of malaria

direct contact with spores on skin surface

symptoms of athlete’s foot

crackling and scaling on foot between toes, can be itchy and sore

examples of plant diseases

tobacco mosaic virus, ring rot, potato/tomato late blight, black sigatoka

means of transmission of tobacco mosaic virus

direct physical contact, infected leaves touching other plants, contaminated tools or workers hands

symptoms of tobacco mosaic virus

colour of leaves turn white or yellow in a mosaic pattern

what type of pathogen is ring rot

bacteria

means of transmission of ring rot

infected tubers lead to growth of new infected plants

symptoms of ring rot

brown staining and then rotting of vascular ring

what type of pathogen is potato/tomato late blight

protoctista

means of transmission of potato/tomato late blight

airborne or water-borne, dispersed by wind or water from infected seeds, tubers producing airborne spores similar to fungi

symptoms of potato/tomato late blight

brown discolouration then rot of leaves or tubers

what type of pathogen is black sigatoka

fungi

means of transmission of black sigatoka

leaf to leaf contact, spread by spores, hyphae penetrate and destroy plant cells

symptoms of black sigatoka

leaves turn black and unable to photosynthesis

factors affecting the transmission of communicable diseases in humans

• overcrowding

• poor nutrition- lowered immune response

• cultural factors e.g. application of non-sterile ointment to open wounds

• lack of sewage system/waste disposal

• no or incomplete immunisation

• shortage of trained medical professionals/underfunded healthcare system

• lack of public awareness/education

• climate change- vectors become more widespread

factors affect transmission of communicable diseases in plants

• overcrowding- monoculture/agriculture

• poor mineral nutrition

• disease resistant GM crops

• climate- damp warm conditions favour survival of pathogen/spores, wind carries spores

• climate change

• migration of new animal vectors to new areas- feed off phloem sap

how can plant defences be classified

passive or active, physical barriers or chemical defences

what is different in plants with diseased tissues than animal

plants do not heal diseases tissues, they seal it off and allow it to die

what are passive plant defence mechanisms

mechanisms which are present all the time

what are the types of passive plant defence mechanisms

physical and chemical

what are physical plant barriers

• waxy cuticle

• bark

• cellulose cell wall

• closing stomata

• resin in bark

• casparian strip in endodermis of root tissue

what are the chemical plant barriers

• secretion of compound that promotes growth of microorganism in competition with pathogen

• secretion of enzyme inhibitors e.g. cellulose inhibitors

• secretion of toxins e.g. mint, garlic, cinnamon, tea tree oil, aloe vera

• sticky resin in bark may contain antibacterial compounds

• receptors on cell surface that detect pathogen and activate plant defences

what are examples of active defence mechanisms of plants

hypersensitivity, systemic acquired resistance, production of callose, production of tyloses, production of phytoalexins, general toxins

what are active plant defence mechanisms

mechanisms brought about as a response to the presence of pathogens

what is hypersensitivity as an active plant defence mechanism

immediate death of tissues surrounding the site of infection

what is systemic acquired resistance as an active plant defence mechanism

• signalling molecule emitted

• travels to uninfected area

• gives protection for some time after infection

• can also transfer to nearby plants if airborne

what is the production of callose as an active plant defence mechanism

deposited between the cell membrane and the cell wall in the plasmodesmata, and in sieve plate pores of phloem sieve tube elements to block movement of pathogen through the plant

what is callose

a branched polysaccharide with 1,3 and 1,6 beta glycosidic bonds

what is the production of phytoalexins as an active plant defence mechanism

produced as a response to breakdown products of cellulose by bacterial and fungal cellulases, defence chemicals that can disrupt cell membrane of bacteria, stimulate the production of enzymes to breakdown cell walls of fungi (chitinases), delay reproduction in pathogens

what are general toxins as an active plant defence mechanism

when some plants are attacked they can make chemicals that can be broken down to cyanide which is toxic to most living things- these plants known as cyogenic

what type of responses are there as defence against infections in animals

innate/non-specific immune response, acquired specific immune response

what lines of defence are there in the innate immune reponse

primary defences, secondary internal defences

what do primary defences in humans do

stop the pathogen from entering the body’s system

what do secondary internal defences in humans do

kill the pathogen when it has entered the system

what is acquired specific immunity

the specific immune response targeted at one particular pathogen developed over the lifetime of the animal and acquired by exposure to a specific antigen, adaptive immunity, all about immunological memory

what type of cells are different in specific and non-specific immune responses

leukocytes

where are blood cells formed

in the bone marrow

which blood cells don’t circulate in the blood

mast cells, macrophages

where are mast cells and what is their function

reside in tissue fluid, produces histamine

what does a neutrophil look like

multi-lobes nucleus

what type of blood cell is a neutrophil

phagocyte

what does a lymphocyte look like

nucleus takes up most of cell

what are the types of membrane on humans

cutaneous, mucous

what is a cutaneous membrane

integument membrane, skin, outer layer is dead, formed from stratified squamous epithelia

what is a mucous membrane

epithelial tissue which secretes mucus, and lines body cavities and tubular organs exposed to the external environment

what are examples of mucous membranes

respiratory tract, digestive tract, urinary tract, reproductive tract

what are the physical and chemical barriers of the human body

lacrimal glands (eyes), ear, skin, large intestines, anus, mouth cavity, lungs-trachea and bronchi, stomach, urinary tract, vagina

how are lacrimal glands (eyes) physical/chemical barriers

solution contains lysozyme- antibacterial

how are ears physical/chemical barriers

cerumen inhibits bacterial growth

how is skin a physical/chemical barrier

impervious to microbes, sebum and sweat secretions provide chemical barrier, increases microbiota (friendly bacteria) which outcompete pathogenic bacteria

how is the large intestine a physical/chemical barrier

gut microbiota protect the body from enteric bacterial infections

how is the anus a physical/chemical barrier

mucus traps microorganisms

how is the mouth cavity a physical/chemical barrier

oral mucosa present a physical barrier, saliva provides a chemical barrier (contains lysozymes)

how are the lungs (trachea and bronchi) physical/chemical barriers

goblet cells secrete mucus to trap pathogens, cilia remove them from airways

how is the stomach a physical/chemical barrier

acidic juices kill most bacteria