communicable diseases Flashcards
1
Q
What are communicable diseases?
A
Diseases that can be passed from one organism to another, of the same or different species • Caused by infective organisms known as pathogens
2
Q
What are pathogens?
A
Microorganisms that cause disease
• Bacteria, viruses, fungi, and
protoctista
3
Q
What are vectors?
A
A living or non-living factor that transmits a pathogen from one organism to another, e.g. malaria mosquito • Common vectors include water and insects
4
Q
Describe bacteria
A
• Prokaryotes, so have no membrane-bound nucleus or organelles Classified in two main ways • By basic shapes: bacilli, cocci, vibrios, spirilla, spirochaetes • By their cell walls: the two main types of cell walls have different structures and react differently with gram staining • Gram positive bacteria look purple-blue e.g. MRSA • Gram negative bacteria appear red e.g. E.coli
5
Q
What are antibiotics?
A
A chemical or compound that kills or
inhibits the growth of bacteria
• The type of cell wall of the bacteria
reactive to different antibiotics
6
Q
What are viruses?
A
• Non-living infectious ages • 0.02-0.3 μm in diameter, so 50x smaller than the average bacterium • Considered by many scientists to be the ultimate parasite
7
Q
Describe viruses
A
• Basic structure is genetic material (DNA or RNA) surrounded by protein • Invade living cells where the genetic material of the virus takes over the biochemistry of the host cell to make more virsuses • All natural viruses are pathogenic - they cause disease in every other type of organism
8
Q
What are bacteriophages?
A
Viruses that attack bacteria • Take over the bacteria cells and use them to replicate, destroying the bacteria at the same time • Can be used to identify and treat some disease, and are very important in scientific research
9
Q
What are protoctista?
A
A group of eukaryotic organisms with a wide variety of feeding methods. Include single-celled organisms and cells group colonies • A small percentage of protoctista act as pathogens, causing diseases in both plants and animals
10
Q
Describe the protists that cause disease
A
They are parasitic - they use people or animals as their host organism • Pathogenic protists may need a vector to transfer them to their hosts e.g. malaria and sleeping sickness • May enter the body directly through polluted water e.g. amoebic dysentery and Giardia
11
Q
What are fungi?
A
Eukaryotic organisms that are often multicellular, although yeasts which cause human diseases e.g. thrush are single-celled • Cannot photosynthesise and digest their food extracellularly before absorbing nutrients • Many are saprophytes (feed on dead and decaying matter) • Some are parasitic (feeding on living plants and animals)
12
Q
Describe the fungi that cause disease
A
Fungal diseases are not a major problem in animals, but they can cause devastation in plants • Pathogenic fungi which cause communicable diseases are parasitic • They often affect the leaves of plants, stopping them photosynthesising, which quickly kills the plant • When fungi reproduce, they produce millions of spore which can spread huge distances, allowing them spread rapidly and widely through crop plants
13
Q
What is the mode of action of viruses?
A
Damaging the host tissues directly • Viruses take over the cell metabolism; the viral genetic material gets into the host cell and is inserted into the host DNA. The host cell is used to make new viruses which the burst out of the cell, destroying it, and then spread to infect other cells
14
Q
What is the mode of action of protoctista?
A
Damaging the host tissues directly • Take over cells and break them open as the new generation emerge, but don’t take over the genetic material of the cell • Digest and use the cell contents as they reproduce e.g. protoctists which cause malaria
15
Q
What are the modes of action of fungi?
A
Damaging the host tissues directly, and producing toxins which damage host tissues • Digest living cells and destroy them • This combined with the response of the body to the damage caused by the fungus gives the symptoms of disease • Some fungi also produce toxins which affect the host cells and cause disease
16
Q
What is the mode of action of bacteria?
A
Producing toxins which damage host tissues • Some bacterial toxins damage the host cell by breaking down the cell membranes • Some damage or inactivate enzymes • Some interfere with the host cell genetic material so that the cells cannot divide • These toxins are a by-product of the normal functioning of the bacteria
17
Q
List some examples of plant diseases
A
- Ring rot (bacterial)
- Tobacco mosaic virus (TMV)
- Potato blight (protoctist)
- Black Sigatoka (fungal)
18
Q
Describe ring rot
A
• Bacterial disease of potatoes, tomatoes and aubergines • Caused by the gram positive bacterium Clavibacter michiganesis • Damages leaves, tubers and fruit • Can destroy 80% of the crop and there’s no cure • Once infected, field can’t be used to grow potatoes again for 2 years
19
Q
Describe Tobacco Mosaic Virus (TMV)
A
Virus that infects tobacco plants, tomatoes, peppers, cucumbers, petunias, and delphiniums • Damages leaves, flowers and fruit, stunting growth and reducing yields • Resistant crop strains are available but there is no cure
20
Q
Describe potato blight
A
• Also tomato blight, late blight • Caused by the fungus-like protoctist oomycete Phytophthora infestans • Hyphae penetrate host cells, destroying leaves, tubes and fruit • No cure but resistant strains, careful management and chemical treatments can reduce infection risk
21
Q
Describe Black Sigatoka
A
Banana disease caused by the fungus Mycosphaerella fijiensis, which attacks and destroys leaves • They hyphae penetrate and digest the cells, turning the leaves black • No cure, but resistant strains are being developed, and good husbandry and fungicide can control the spread of the disease
22
Q
List some examples of animal diseases
A
- Tuberculosis (TB)
- Bacterial meningitis
- HIV/AIDS
- Influenza (flu)
- Malaria
- Ring worm
- Athlete’s foot
23
Q
Describe Tuberculosis (TB)
A
• Bacterial disease • Humans, cows, pigs, badgers and deer • Caused by; Mycobacterium tuberculosis and M. bovis • Damages and destroys lung tissue and suppress the immune system • Curable by antibiotics, and preventable by improving living standards and vaccination
24
Q
Describe Bacterial Meningitis
A
• Bacterial infection of the meninges of the brain • Can spread to the rest of the body causing septicaemia (blood poisoning) and rapid death • Many affects very young children and teenagers • Symptoms: blotchy red/purple rash that doesn’t disappear when a glass is pressed against it • Antibiotics cure it if delivered early • Vaccines protect against some forms of it
25
Q
Describe HIV/AIDS
A
• AIDS (acquired immunodeficiency syndrome) is caused by HIV (human immunodeficiency virus) • Targets T helper cell in the immune system of the body • Gradually destroys the immune system, so affect people of open to other infections e.g. TB, pneumonia, and some types of cancer • Affects humans and some nonhuman primates • HIV is a retrovirus with RNA as its genetic material • Contains the enzyme reverse transcriptase, which transcribes the RNA to a single strand of DNA to produce a single strand of DNA in the host cell • This DNA interacts with the genetic material of the host cell • The virus is assed from one person to another in bodily fluids e.g. unprotected sex, shared needles, contaminated blood products, and from mother to child during pregnancy • No vaccine and no cure, by antiretroviral dress slow the progress of the disease
26
Q
Describe Influenza (flu)
A
• Viral infection • Kills the ciliated epithelial cells in the gas exchange system, leaving the airways open to secondary infection • Can be fatal to young children, old people, and people with chronic illnesses • Many of the deaths are from severe secondary bacterial infection on top of the original viral infections e.g. pneumonia • Affects mammals including humans, pigs, birds (inc. chickens) • 3 Strains (A,B,C); A are the most virulent • Flu viruses mutate regularly • Vulnerable groups are given a vaccine annually to protect against changing strains • No cure
27
Q
Describe Ring Worm
A
• Fungal disease • Mammals including cattle, dogs, cats and humans • Different fungi affect different species • Causes grey-white, crusty, infectious circular areas of skin • Not damaging, but looks unsightly and may be itchy • Anti fungal creams are an effective cure
28
Q
Describe Athlete’s Foot
A
• Human fungal disease • Caused by Tinia pedia, a form of human ring worm that grows on and digests the warm, moist skin between the toes • Causes cracking and scaling, which is itchy and may become sore • Anti fungal creams are an effective cure
29
Q
Describe Malaria
A
• Caused by the protoctista Plasmodium, and spread by the bites of infected Anopheles mosquitoes • Plasmodium parasite has a complex life cycle with two hosts - mosquitoes and people • Reproduce inside the female mosquito • The female needs to take two blood meals to provide her with protein before she lays her eggs - this is when Plasmodium is passed onto people • Invades red blood cells, liver and brain • No vaccine, limited cures • Killing the mosquito through insecticides • Removing standing water, mosquito nets, wind and door screen, long sleeved clothing etc
30
Q
What is direct transmission (animals)?
A
When a pathogen is transferred directly from one individual to another by: • Direct contact (contagious diseases) • Inoculation • Ingestion
31
Q
Give details of the methods of direct transmission
A
Direct contact (contagious diseases): • Kissing or any contact with the body fluids of another person e.g. bacterial meningitis and many STDs • Direct skin-to-skin contact, e.g. ring worm, athlete’s foot • Microorganisms from faeces transmitted not the hands, e.g. diarrhoea diseases Inoculation • Through a break in the skin, e.g. during sex (HIV/AIDS) • From an animal bite (e.g. rabies) • Through a puncture wound on through sharing needles, e.g. septicaemia Ingestion • Taking in contaminated food or drink, or transferring pathogens to the mouth from the hands, e.g. amoebic dysentery, diarrhoeal diseases
32
Q
What is indirect transmission (animals)?
A
Where the pathogen travels from one individual to another indirectly • Fomites • Droplet infection (inhalation) • Vectors • Transmission between animals and humans
33
Q
Give details of the methods of indirect transmission
A
Fomites: • Inanimate object e.g. bedding, socks or cosmetics, can transfer pathogens such as athlete’s foot, gas gangrene, and Staphylococcus infections Droplet infection(inhalation): • Minute droplets of saliva and mucus expelled from the mouth as you talk, cough or sneeze • If droplets contain pathogens, when healthy individuals breathe them in, they may become infected e.g. TB, influenza Vectors: • Transmit communicable pathogens between hosts • e.g. mosquitoes transmit malaria, rat fleas transmit bubonic plague, dogs, foxes and bats transmit rabies Between animals and humans • e.g. Bird flu strain H1N1, and brucellosis (sheep to people) • Minimising close contact with animals and washing hands • Vice versa e.g. foot-and-mouth disease
34
Q
What are the factors affecting
the transmission of
communicable diseases in
animals?
A
Overcrowded living and working conditions • Poor nutrition • Compromised immune system, e.g. having HIV/AID, or needing immunosuppressant drugs after transplant surgery • (in humans) Poor disposal of waste, providing breeding sites for vectors • Climate change - can introduce new vectors and diseases, e.g. increased temperatures promote the spread of malaria • Culture and infrastructure - in many countries, traditional medical practises can increase transmission • Socioeconomic factors - e.g. lack of trained health workers and insufficient public waning when there is an outbreak of disease
35
Q
What is direct transmission in plants?
A
The direct contact of a healthy plant
with any part of a diseased plant
e.g. TMV, tomato and potato blight,
and black Sigatoka
36
Q
What are the types of indirect transmission in plants?
A
- Soil contamination
* Vectors
37
Q
Describe soil contamination
A
Infected plants often leave pathogens (bacteria or viruses), or reproductive spores from protoctista or fungi in the soil • Theses can infect the next crop • e.g. black Sigatoka spores, ring rot bacteria, spores of P. infestans, and TMV • Some pathogens (often as spores) can survive the composting process, so the infection cycle can be completed when contaminated compost is used
38
Q
Describe vectors in plants
A
Wind • Bacteria, viruses and fungal or oomycete spores my be carried on in the wind • e.g. Black Sigatoka blown between Caribbean islands, P. Infestans sporangia form spores, which are carried by the wind to other potato crops/ tomato plants Water • Spores swim in the surface film water on leaves • Raindrop splashes carry pathogens and spores etc • e.g. spores of P. infestans (potato blight) which swim over films of water on leaves Animals • Insects and birds carry pathogens and spores from one plant to another as they feed • Insects such as aphids inoculate pathogens directly into plant tissues Humans • Pathogens and spores are transmitted by hands, clothing, fomites, farming practices and by transporting plants and crops around the world • e.g. TMV survives for years in tobacco products • Ring rot survive on farm machinery, potato sacks etc.
39
Q
What are the factors affecting
the transmission of
communicable diseases in
plants?
A
• Planting varieties of crops that are susceptible to disease • Over-crowding increases the 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 the spread of diseases; changing conditions allow animal vectors to spread to new areas; drier conditions may reduce the spread of disease
40
Q
Give basic ways in which plants defend themselves
against pathogens
A
Waxy cuticle of leaves, bark on trees
and cellulose cell walls of individual
cells all act as barriers preventing
pathogens from getting in
41
Q
What is the difference between plant and animal responses to diseased tissue?
A
Unlike animals, plants don’t heal diseased tissue - they seal it off and sacrifice it • Because they are continually growing at the meristems, they can then replace the damaged parts
42
Q
How do plants recognise an attack?
A
1. Receptors in the cells respond rapidly to pathogen attacks 2. Receptors in the cells respond to molecules from the pathogens, or to chemicals produced when the plant cell wall is attacked 3. This stimulates the release of signalling molecules that appear to switch on genes in the nucleus 4. This triggers cellular responses including: • Producing defensive chemicals • Sending alarm signals to unaffected cells to trigger their defences • Physically strengthening the cell walls
43
Q
What is callose?
A
A polysaccharide containing ß 1-3 linkages and ß 1-6 linkages between the glucose monomers that is important in the plant response to infection
44
Q
What role does callose play in plant physical defences?
A
Callose papillae: • Within minutes of an initial attack callose is synthesised and deposited between the cell walls an cell membrane in the cells adjacent to infected cells • These act as barriers, preventing the pathogens entering the plant cells around the site of infection • Large amounts of callose continue to be deposited in cell walls after the initial infection. Lignin is added, making the mechanical barrier to invasion even thicker and stronger • Callose blocks sieve plates in the phloem, sealing off the infected part and preventing the spread of pathogens • Callose is deposited in the plasmodesmata between infected cells and their neighbours, sealing them off from the healthy cells and helping to prevent the pathogen spreading
45
Q
What happens in xylose formation?
A
This is when the xylem is blocked from carrying water by a terpenefilled swelling called a xylose. This prevents pathogens moving through the xylem
46
Q
Give examples of plant chemical defences
A
• Insect repellents e.g. pine resin and 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 • Antifungal compounds • Anti-oomycetes e.g. glucanases (enzymes made by some plants that break down glucans; polymers found in the cell walls of oomycetes e.g. P. infestans) • General toxins - some plants make chemicals that can be broken down to form cyanide compounds when the plant is attacked
60
Q
What are the stages of phagocytosis?
A
1. Pathogens produce chemicals that attract phagocytes 2. Phagocytes recognise nonhuman proteins on the pathogen. This is a respondent to a specific type of pathogen, but simply a cell or organism that is non-self 3. The phagocyte engulfs the pathogen and encloses it in a vacuole called a phagosome 4. The phagosome combines with a lysosome to form a phagolysosome 5. Enzymes from the lysosome digest and destroy the pathogen
68
Q
Describe antibodies in detail
A
• Y-shaped glycoproteins called immunoglobulins • Bind to a specific antigen on the pathogen or toxin that has triggered the immune response • Specific antibody for each antigen • Made up of two identical long polypeptide chains called heavy chains, and two much shorter chains called the light chains • The chains are held together by disulphide bridges, and there are also disulfide bridges within the polypeptide chains holding them in shape
85
Q
What are the stages in cell mediated immunity?
A
1. In the non-specific defence system, macrophages engulf and digest pathogens in phagocytosis. They process the antigens from the surface of the pathogen to form APCs 2. The receptors on some the T helper cells fit the antigens. These cells become activated and produce interleukins which stimulate more T cells to divide by mitosis. They form clones of activated T helper cells that all carry the right antigen to bind to a particular pathogen 3. The cloned T cells may: • Develop into T memory cells • Produce interleukins that stimulate phagocytosis • Produce interleukins that stimulate B cells to dive • Stimulate the development of a clone of T killer cells that are specific for the presented antigen and then destroy infected cells
88
Q
What are the steps in humoral immunity?
A
1. Activated T helper cells bind to the B cell APC. This is clonal selection - the point at which the B cell with the correct antibody to overcome a particular antigen is selected for cloning 2. Interleukins produced by the activated T helper cells activate the B cells 3. The activated B cell divides by mitosis to give clones of plasma cells and B memory cells. This clonal expansion 4. Primary immune response: Cloned plasma cells produce antibodies that fir the antigens on the surface of the pathogen, bind to the antigens and disable them, or act as opsonins or agglutinins 5. Secondary immune response: Some cloned B cells develop into B memory cells. If infected by the same pathogen again, the B memory cells die rapidly to form plasma cell clones
