12- Communicable diseases

Question 1

What is a communicable disease?

Answer 1

-caused by pathogens
-spread between organisms
-cause around 23% all of deaths globally per year

Question 2

Definition of a pathogen

Answer 2

microorganisms which can cause disease

Question 3

What are the different types of pathogen?

Answer 3

Bacteria
Virus
Fungi
Protoctista (protista)

Question 4

What is a vector?

Answer 4

carry pathogens from one organism to another, and are involved in the spread of a number of important plant and animal diseases
eg. water, insects

Question 5

What is a host?

Answer 5

organism which pathogen infects

Question 6

What is bacteria and its structure?

Answer 6

-prokaryotes
-no membrane-bound organelles or nucleus
-classified by their shapes and cell walls
-shapes include rod shapes, spherical, comma shaped, spiralled, corkscrew
-cell wall, two main types which react differently with gram staining
gram positive = purple-blue eg. MRSA
gram negative = red eg. E.coli

Question 7

What are viruses, its structure and function

Answer 7

-non living infectious agents
-0.02-0.03 μm in diameter
-50x smaller then bacteria
-no cellular structure
-genetic material (DNA or RNA) wrapped in a protein structure called capsid
-have attachment proteins which attach to host cells
-cannot reproduce outside of host cell
-invade living cells, genetic material of viruses takes over biochemistry of cells to make more viruses
-can lead to death of host cell

Question 8

What are protoctista, its structure and function

Answer 8

-eukaryotic organisms with a variety of feeding methods
-include single celled organisms and cells groups in colonies
-parasitic, use people/animals as there host
-may need a vector to transfer to host (eg. malaria) or may enter body through polluted water (eg. giardia)

Question 9

What is fungi, its structure

Answer 9

-eukaryotic organisms
-often multicellular (yeasts are single cellular)
-cannot photosynthesise and digest there food extracellularly before absorbing the nutrients
-obtain nutrients by releasing enzymes and digesting material around them
-processes of digestion= cause damage to host cells and tissues
-reproduce and release spores which can spread widely
-pathogenic fungi eg. thrush, athletes foot
-can also cause disease in plants

Question 10

How do viruses damage host cells directly?

Answer 10

-take over cell metabolism
-viral genetic material gets into the host cell and is inserted into the host DNA
-viruses uses the host cell to make new viruses which then burst out of the cell, destroying it and then spread to infect other cells

Question 11

How do bacteria damage host tissues?

Answer 11

-produce toxins that poison or damage the host cells
-some damage host cells by breaking down the cell membranes, some inactivate enzymes and some interfere with genetic material so cells cannot divide

Question 12

How do fungi damage host cells?

Answer 12

-digest living cells and destroy them, this combined with the body’s response to damage causes the symptoms of the disease
-some produce toxins which affect the host cells and cause disease

Question 13

How do protoctista damage host cells?

Answer 13

-some take over cells and break them open as the new generation emerge but do not take over genetic material of the cell
-simply digest and use the cell contents as they reproduce

Question 14

What is ringrot?

Answer 14

-bacterial diease
-potatoes, tomatoes, aubergines
-damages leaves, tubers and fruit
-can destroy up to 80% of crops
-no cure
-transmitted through infected tubers and seeds
-discolouration of vascular ring
-infects a field then cannot be used to grow potatoes for at least 2 years
-remove infected plants to prevent transmission

Question 15

What is tobacco mosaic virus?

Answer 15

-plant disease
-virus
-infects tobacco plants and 150 other species including tomatoes and peppers
-damages leaves, flowers and fruit
-stunts growth and reduces yields
-resistant crop strains are avaliable but no cure

Question 16

What is potato/tomato blight?

Answer 16

-plant disease
-fungus like prtoctista
-hyphae penetrate host cells, destroying leaves, tubers and fruit
-no cure
-resistant strains, careful management and chemical treatments can reduce infection risk
-spread by wind and water splash

Question 17

What is black sigatoka?

Answer 17

-plant disease
-fungal
-bananas
-attacks and destroys leaves
-hyphae penetrates leaves and digests the cells turning leaves black
-cause a 50% yield decrease
-resistant strains being developed
-fungicide treatment but no cure
-spread can occur from rain splash and wind borne spores
-spread particularly in wet, humid and windy conditions

Question 18

What is tuberculosis?

Answer 18

-animals disease
-bacterial disease of humans, cows, pigs, badgers and deer
-damages and destroys lung tissue and suppresses the immune system
-usually passes through air when infected, coughs, sneezes etc.
-increase in people with HIV/AIDS has an impact of the number of people with TB
-curable by antibiotics
-preventable by improving living standards and vaccination
-common in poorly ventilated, overcrowded areas

Question 19

What is bacterial meningitis?

Answer 19

-animal disease
-bacterial infection of the meninges of the brain
-can spread to the rest of the body causing septicaemia and rapid death
-mainly affects young children and teenagers aged 15-19
-blotchy red/purple rash that does not disappear when a glass is pressed against (in both types)
-10% will die
-antibiotics will cure if delivered early
-vaccines can prevent against some forms
-transmitted from person to to person through droplets

Question 20

What is HIV?

Answer 20

-animal disease
-human immunodeficiency virus
-targets T helper cells in the immune system
-gradually destroys the immune system so infected are open to other infection (eg. TB, pneumonia)
-affect humans and some other non-human primates
-passed from one person to another in bodily fluids eg. unprotected sex
-no vaccine or cure but anti-retroviral drugs slow down the process of disease
-africa most affected

Question 21

What is influenza?

Answer 21

-animal disease
-viral infection of the ciliated epithelial cells in the gaseous exchange system
-it kills them leaving airways open to secondary infection
-can be fatal in young children, old people and those chronically ill
-affects mammals including humans, pigs,birds
-may deaths from severe secondary infection
-3 main strains
-vulnerable groups given vaccine annually to protect against ever changing strains
-no cure

Question 22

What is malaria?

Answer 22

-animal disease
-caused by protoctista Plasmodium
-spreads by bites of infected female anophles mosquitoes
-invade RBC’s, liver and brain
-no vaccine, limited cures but are preventable measures
-key= control measures (eg. insecticides, removing water where they breed, mosquito nets, window and door screens, long sleeves)

Question 23

What is ring worm?

Answer 23

-animal disease
-fungal disease
-affects mammals including humans, cattle, dogs, cats
-different fungi affect different species
-causes grey-white, crusty, infectious, circular areas of skin
-antifungal creams = cure
-spread by direct skin-skin contact

Question 24

What is athletes foot?

Answer 24

-human fungal disease
-form of human ring worm
-grows and digests the warm, moist skin between toes
-causes cracking and scaling which is itchy and may be sore
-antifungal creams
-skin-skin contact

Question 25

What are the two main types of transmission?

Answer 25

Direct
Indirect

Question 26

What is direct transmission?

Answer 26

Pathogen is transmitted directly from one individual to another

Question 27

What are examples of direct transmission in animals?

Answer 27

Direct contact -
•kissing, contact with bodily fluids eg. STD’s and bacterial meningitis
•direct skin-skin contact eg. ring worm, athletes foot
•microorganisms from faeces transmitted on the hands eg. diarrhoeal diseases
Inoculation-
•break in the skin eg. during sex, HIV
•from an animal bite eg. rabies
•puncture wound or sharing needle eg. septicaemia
Ingestion
•taking in contaminated food or drink, transferring pathogens from hands to mouth eg. diarrhoeal diseases

Question 28

What are examples of indirect transmission in animals?

Answer 28

Fomites-
•inanimate objects like bedding, socks can transfer pathogens eg. athletes foot, gas gangreen
Droplet Infection-
•minute droplets from mouth, saliva are expelled from mouth when you talk, cough, sneeze. If droplets contain pathogens, when healthy individuals breathe the droplets in they may become infected eg. influenza, tuberculosis
Vectors-
•vector transmits communicable pathogens from one host to another eg. mosquitoes, water

Question 29

What is a vector?

Answer 29

something that transmits communicable pathogens from one host to another

Question 30

What is indirect transmission?

Answer 30

-Pathogens travels from one organism to another indirectly
-A second organisms that is unaffected by pathogen transfers it to a new host or the pathogen is transferred by inanimate objects or through aerosol droplets being inhaled

Question 31

What are the factors that increase the probability of a person catching a communicable disease?

Answer 31

-overcrowded living and working conditions
-poor nutrition
-a compromised immune system
-poor disposal of waste, providing breeding sites for vectors
-climate change (can introduce new vectors and disease. increased temps promote spread of malaria as mosquito species is able to survive over wider area)
-culture and infrastructure (in countries traditional medical practices can increase transmission)
-socioeconomic factors (eg. lack of trained health workers and insufficient public warning when there is an outbreak of disease)

Question 32

What is and what are examples of direct transmission in plants?

Answer 32

-direct contact of a healthy plant with any part of a diseased plant
eg. ring rot, TMV, potato blight, black sigatoka

Question 33

What is and what are examples of indirect transmission in plants?

Answer 33

Soil Contamination-
•infected plants leave pathogens or reproductive spores from protists or fungi in the soil, these can infect next crop
Vectors-
•wind - bacteria, viruses, fungi, oomycete spores may be carried in the wind
•water -spores swim in surface film of water on leaves, rain droplets carry pathogens and spores
•animals - insects and birds carry pathogens and spores from one plant to another as they feed
•humans - pathogens and spores are transmitted by hands, clothing, farming practices and by transporting crops around the world

Question 34

What are the factors that increase the probability of a plant catching a communicable disease?

Answer 34

-planting varieties of crops that are susceptible to diease
-overcrowding increases likelihood of contact
-poor mineral nutrition reduces resistance of plants
-damp, warm conditions increase the survival and spread of pathogens and spores
-climate change = increased rainfall and wind promote spread of diseases, changing conditions allow animal vectors to spread to new areas, drier conditions may reduce spread of disease

Question 35

What are the key factors in reducing the spread of communicable diseases in plants?

Answer 35

leave plenty of room between plants to minimise contact
clear fields as thoroughly as possible, remove all traces of plant in soil when harvesting
rotate crops, spores or bacteria will eventually die if they do not have access to host
follow strict hygiene practices
control insect vectors

Question 36

How do plants recognise an attack?

Answer 36

-receptors in the cells respond to molecules from the pathogens or produce chemicals when the plant cell wall is being attacked
-this stimulates the release of signalling molecules that appear to switch on genes in the nucleus
-this in turn triggers cellular responses eg. producing defensive chemicals to give alarm to other cells before being attacked, sending alarm signals, physically strengthening the cell wall by making callose and lignin

Question 37

What is the physical defences of plants against pathogens?

Answer 37

-within minutes of the initial attack, callsoe is synthesised and deposited between cell walls and the cell membrane in the cells next to the infected cells. Callose acts as barrier preventing pathogens entering cells
-callose continues to be deposited in cell wall after initial infection. Lignin is added, making the mechanical barrier thicker and stronger
-Callose blocks sieve plates in the phloem, sealing off infected part and preventing the spread of pathogen
-Callose is deposited in the plasmodesmata between infected cells and their neighbours, sealing them off from healthy cells and prevent spread of pathogen

Question 38

What is the chemical defences of plants against pathogens?

Answer 38

-insect repellants eg. pine resin, citronella from lemon grass
-insecticides eg. pyrethrins made by chrysanthemums and act as insect neurotoxins, caffeine toxic to plants and fungi
-antibacterial compounds eg. lysosomes continuing enzymes which break down bacterial cell walls
-antifungal compounds eg. chitnases, enzymes that break down the chitin in fungal cell walls
-anti-oomycetes eg. glucanes, enzymes which break down glucans (polymers found in the cell walls of oomycetes)
-general toxins eg. some plants make chemicals that can be broken down to form cyanide compounds, cyanide is toxic to most living things