Communicable Diseases Flashcards
Viruses
Non living
0.02-0.3 micrometers (50x smaller than bacteria)
They are DNA/RNA surrounded by protein shells
Invade living cells and take over biochemistry, so host makes more viruses
Rapidly evolve
Always pathogenic
Bacteria
Small proportion are pathogens
All Prokaryotes (no membrane bound nucleus or organelles)
Classified in two ways:
Basic shape- rod, spherical, comma, spiralled and corkscrew shaped
Cell walls- there are two main types, have different structures and react differently with process called Gram staining.
Following staining you have Gram positive and Gram negative bacteria
(useful to know as they act differently to different antibodies, the cell wall).
Whats a pathogen
Examples
An organism that causes disease
Bacteria, viruses, fungi and protoctista
What’s a disease
A condition that impairs the normal functioning of an organism
Communicable disease definition
A disease that can spread between organisms
Tuberculosis (TB)
Pathogen responsible and affects
Bacterium
Animals, typically humans and cattle
Bacterial meningitis
Pathogen responsible and affects
Bacterium
Humans
Ring rot
Pathogen responsible and affects
Bacterium
Potatoes and Tomatoes
HIV/AIDS
Pathogen responsible and affects
Virus
Humans
Influenza
Pathogen responsible and affects
Virus
Animals, including humans
Tobacco mosaic virus
Pathogen responsible and affects
Virus
Plants
Black sigatoka
Pathogen responsible and affects
Fungus
Banana plants
Ringworm
Pathogen responsible and affects
Fungus
Cattle
Athlete’s foot
Pathogen responsible and affects
Fungus
Humans
Potato/tomato late blight
Pathogen responsible and affects
Protoctist
Potatoes and Tomatoes
Malaria
Pathogen responsible and affects
Protoctista
Animals, including humans
The two ways communicable diseases can be transmitted
Directly or indirectly
Direct transmission
Examples
When the disease is transmitted directly from one organism to another
Can happen in several ways: droplet infections (sneezing coughing) sexual intercourse or touching
Examples: HIV via sexual intercourse
Athlete’s foot via touch
Indirect transmission
Examples
When the disease is transmitted from one organism to another via an intermediate (i.e air, water, food, or another organism- vectors)
Examples: potato late blight spread when spores are carried between plants (first air then water)
Malaria spread via mosquitoes (act as vectors).
What three factors can affect disease transmission
Climate
Living conditions
Social factors
Overcrowded living conditions affect
Example
Increases the transmission of any communicable diseases
Eg: Tuberculosis spreads directly via droplets and indirectly remains in the air for long periods of time
Climate affect
Examples
Potato/ tomato late blight common during wet summers because spores need water to spread
Malaria most common tropical countries, humid and hot (ideal conditions for mosquitoes to breed)
Social factors affect transmission of communicable disease
Examples
In humans social factors can increase it
Risk HIV infection is high in places where there's limited access to: Good healthcare (less likely to be diagnosed and treated) Good health education (inform how it is transmitted and how it can be avoided)
Animals have several barriers to prevent infection, pathogens need to enter an organism in order to cause disease. So most animals have what?
A range of primary non-specific defences to help prevent this from happening
Non specific defense
Skin
Acts physical barrier, blocking pathogens from entering body.
Also acts as chemical barrier by producing chemicals that are antimicrobial and lower the pH, inhibiting growth of pathogens
Non specific defences
Mucous membranes
Protects bodies openings that are exposed. Some membranes secrete mucus (sticky substance that traps pathogens and contains antimicrobial enzymes)
Non specific defense
Blood clotting
Blood clot is mesh of protein (fibrin) fibres.
It clots plug wounds to prevent pathogen entry and blood loss.
They’re formed by series chemical reactions that take place when platelets are exposed to damaged blood vessels
Non specific defense
Inflammation
Can be triggered by tissue damage- damaged tissue releases molecules, which increases permeability of the blood vessels, so they leak fluid into surrounding area. Causing swelling and helps to isolate pathogens within damaged area. Vasodilation occurs increasing blood flow making the area hot bringing white blood cells to the area
Phagocytes
Phagocytes are found in the blood stream (blood vessels)
Origin: bone marrow
Phagocyte process
Pathogen is engulfed by phagocyte
- pathogen is packaged inside a phagosome (a vesicle)
- phagosome fuses with lysosome(s) -> phagolysosome
- enzymes (hydrolitic, lysins) from lysosome digest the pathogens (by hydrolysis)
- antigens displayed in membrane of phagocytes (using MHC proteins), if the phagocyte is a macrophage
- It now becomes an antigen presenting cell (APC)
- The soluble debris is removed by exocytosis, useful substances are absorbed into cytoplasm.
Main types of T lymphocytes
T-killers
T-helpers
T-memory
T-regulator cells
T-killer cells
T killer cells- destroy infected cells carrying the antigen. They produce chemical called perform, which kills by making holes in the cell membrane so its freely permeable
T-helper cells
T helper cells- have CD4 receptors on their cell-surface membranes, which bind to the surface antigens on APC’s. They produce interleukins (type of cytokine). The interleukins stimulate the activity of B cells, which increases antibody production, stimulates production of other types of T cells and attracts and stimulates macrophages to ingest pathogens with antigen- antibody complexes.
T-memory cells
T memory cells- live for a long time, part of the immunological memory. If they meet antigen a second time, they divide rapidly to form huge number of clones of T killer cells that destroy the pathogens.
T-regulator cells
T regulator cells- they suppress the immune system, acting to control and regulate it. They stop the immune response once the pathogen has been eliminated, and make sure the body recognises self antigens and doesn’t set up the autoimmune response. Interleukins are important in this control.
Cell-mediated immunity
In cell-mediated immunity, T lymphocytes respond to the cells of an organism that have been changed in some way (I.e from virus, antigen processing, mutations or transplanted tissue). It’s particularly important for viruses and early cancers.
-In non specific innate defence systems, phagocytes engulf and digest pathogens in phagocytosis. They process the antigens from the surface of the pathogen and display them on their cell membrane (becoming APCs).
Main types of B lymphocytes
Plasma cells- produce antibodies to a particular antigen and release them into the circulation (an active plasma cell only lives for few days but produces around 2000 antibodies per second).
B effector cells- these divide to form the plasma cell clones
B memory cells- live very long and provide immunological memory. Programmed to remember a specific antigen, and enable the body to make a rapid response when a pathogen carrying that antigen is encountered again.
Lines of defense
1) Innate non-specific (primary) defences- keeping pathogens out Skin (keratinocytes; flora; sebum) Mucous membranes (mucus, lysozomes, phagocytes) Expulsive reflexes (coughing, sneezing vomiting diarrhoea) Blood clotting (platelets, thromboplastin, serotonin) Inflammatory response (mast cells, histamines, cytokines)
2) Innate non-specific (secondary) defences- getting rid of pathogens
Phagocytes (neutrophils and macrophages; phagocytosis; antigen presentation)
Chemical messengers (cytokines; opsonins)
Fever (body temp increases, becomes more hostile for bacteria to thrive).
3) Adaptive specific immune response- targeting pathogens; immunity
Lymphocytes (B cells and T cells; immunological memory)
Physical plant defences
When attacked, rapidly set up mechanical defence. Produce high levels of cal lose (a polysaccharide) which
contains beta-1,3 linkages and beta-1,6 linkages between the glucose monomers.
-Callose is synthesised and deposited between the cell walls and the cell membrane in cells next to the
infected one. These callose papillae act as barriers (prevent spread).
-Callose is continuously added. Lignin is added also making the mechanical barrier to invasion even thicker
and stronger.
-Callose blocks sieve plates in phloem, sealing off the infected part and prevent spread of pathogens.
-Callose deposited in the plasmodesmata between infected cells and their neighbours p, sealing them off
from healthy cells and helping prevent spread.
Chemical Plant Defences
Many produce powerful chemicals, either repel the insect vectors of disease or kill invading pathogens.
Examples of plant defensive chemicals include:
Insect repellents- e.g pine resin an pd citronella from lemon grass
Insecticides-e.g pyrethrins made by chrysanthemums and act as insect neurotoxins; and caffeine (toxic to
insects and fungi).
Antibacterial compounds including antibiotics- e.g phenols, antiseptics made in many different plants,
antibacterial gossypol produced by cotton.
Antifungal compounds- e,g chitinases- enzymes that break down the chitin in fungal cell walls.
Anti-oomycetes- e.g glucanases, enzymes made by some plants that break down glucans (polymers found in
the cell walls of oomycetes).
General toxins- some make chemicals that can be broken down to form cyanide compounds when the plant cell
is attacked (cyanide is toxic to most living things).
Culture and infrastructure affect transmission
In many countries traditional medical practices can increase transmission
Socioeconomic factors affect transmission
E.g a lack of trained health workers and insufficient public warning when there is an
outbreak of diseases can also affect transmission rates.
The adaptive, specific immune response
- The adaptive, specific immune response is activated by the non-specific, innate immune system
- provides immune system with the ability to:
- Recognise and remember specific pathogens ‘immunological memory’
- Mount stronger attacks each time pathogens encountered primary immune response and secondary immune response
Lymphocytes
- Smaller than phagocytes
- larger nucleus that almost fills the cell
- made in bone marrow
B Lymphocytes
-remain in bone marrow until mature
-congregate in lymph nodes and spleen
-have highly specific antibodies in membrane,
each B cell can only produce one type of antibody
and the B cell is unique.
-once the correct B cell is selected, the cell is
cloned and stimulated to differentiate to produce
plasma/ effectors cells (which produce antibodies)
and memory cells.
-Attack pathogens in circulation as part of the
‘humoral response’ (in the body fluids).
T Lymphocytes
-mature in thymus
-have highly specific receptors in membrane
-once correct T cell is activated, T cells with various
jobs can be produced (‘helpers’, ‘killers’, ‘memory’,
‘regulators’).
-control and coordinate everything
-attack infected cells as part of the ‘cell mediated
response’.
Non specific defences- keeping pathogens out
Barriers
-The skin covers the body and prevents the entry of pathogens. Has skin flora of healthy microorganisms that
outcompete pathogens for space on the body surface. Skin produces sebum too, oily substance inputs the growth
of pathogens.
-Many of the body tracts are lined with mucous membranes that secrete sticky mucus, trapping microorganisms
and contains lysozymes, which destroy bacterial and fungal cells walls. Mucus also contains phagocytes, which
remove remaining pathogens.
-Lysozymes in tears and urine, and the acid in the stomach also help to prevent pathogens getting into the body.
-Expulsive reflexes, coughs and sneezes eject pathogen-laden mucus from the gas exchange system, while
vomiting and diarrhoea expel the contents of the gut along with any infective pathogen.
Non specific defences- keeping pathogens out
Blood clotting and wound repair
-Thromboplastin, an enzyme that triggers cascade of reactions resulting in formation of blood clot (thrombus)
-Serotonin, makes the smooth muscle in the walls of the blood vessels contract, reduce blood flow to that area.
-Clot dries out, creating hard tough scab keep pathogens out. Then epidermal cells below begin to grow, sealing
the wound permanently while damaged blood vessels regrow. Collagen fibres are deposited to give the new tissue
strength. Once epidermis reactions normal thickness, scab sloughs off and the wound is healed.
Non specific defences, keeping pathogens out
Inflammatory response
It’s a localised response to pathogens (or damage or irritants) resulting in inflammation at site of wound.
Mast cells are activated in damaged tissue and release chemicals called histamines and cytokines.
-Histamines make blood vessels dilate, causing localised heat and redness. The raised temperature helps
prevent pathogens reproducing.
-Histamines make blood vessel walls more leaky so blood plasma is forced out, once forced out of the
blood known as tissue fluid, which causes swelling (oedema) and pain.
-Cytokines attract white blood cells (phagocytes). They dispose of pathogens by phagocytosis.
Factors that affect transmission of communicable diseases in plants
Planting variety of crops Over-crowding Poor mineral nutrition Damp, warm conditions Climate change They become more sustainable to disease Increases the likelihood of contact Reduces resistance of plants Increases the survival and spread of pathogens and spores Increased rainfall and wind promote the spread of diseases; changing conditions allow animal vectors TPS Read to new areas; drier conditions may reduce the spread of disease.
Direct transmission in plants
involves direct contact of healthy plant with any part of a diseased plant (ring rot, tobacco
mosaic virus TMV, tomato and potato blight, and black sigatoka.
Indirect transmission in plants
Soil contamination: infected plants often leave pathogens or reproductive spores in the soil. These can infect
the next crop (black sigatoka spores, ring rot bacteria, spores of infestans and TMV). Some pathogens can
survive the composing process so the infection cycle can be completed when contaminated compost is used.
Examples of vectors for plants
Wind: pathogens (spores) may be carried on by the wind
Water: spores swim in the surface film of water on leaves; raindrop splashes carry pathogens and spores.
Animals: insects and birds carry pathogens and spores as they feed from one plant to another. Insects such as
aphids inoculate pathogens directly into the plant tissues.
Humans: pathogens and spores transmitted by hands, clothing, fomites, farming practices and by transporting
plants and crops around the world.
Direct transmission
Ingestion
Taking in contaminated food or drink, or transferring pathogens to the mouth from the hands (amoebic dysentery, diarrhoeal diseases). Control measures: keep hands clean, and avoid touching facial area when possible, making sure food is cooked well/properly and not infected (good food hygiene practices)
Direct transmission Direct contact (contagious disease)
Kissing, or any contact with body fluids
(e.g bacterial meningitis and STD’s).
Direct skin to skin contact (e.g ring worm,
athlete’s foot). Microorganisms from
faeces transmitted on the hands (e.g
diarrhoeal diseases).
Control measures: frequently wash
hands, use protection during any sort of
sexual interaction and be aware if you
carry an STD.
Direct transmission
Inoculation
Through a break in the skin (e.g during sex HIV/AIDS).
From an animal bite (rabies)
Through a puncture wound or through sharing needles
(septicaemia)
Control measure: wear protection during sexual acts (be aware
of any STD’s you may carry), clean and disinfect any wounds,
and sterilise equipment
Indirect transmission Droplet infection (inhalation)
Minute droplets of saliva and mucus are expelled from your mouth when
you talk/ sneeze. If droplets contain pathogens, when healthy individuals
breathe the droplets in they may become infected (influenza, tuberculosis).
Control measures: good ventilation, wear a mask
Indirect transmission
Fomites
Inanimate (not alive) objects such as bedding or cosmetics can transfer pathogens (athlete’s foot, gas gangrene and staphylococcus infections). Control measures: to constantly wipe down and sterilise surface, and minimise amount of object you come into contact with.
Indirect transmission
Vectors
Transmits communicable pathogens from
one host to another. Vectors often but not
always animals (mosquitoes pass on
malaria, rat fleas pass on bubonic plague,
dogs foxes and bats pass on rabies).
Water can also act as a vector (diarroheol
disease).
Control measures: elimination or
management of larval habitats,
