Communicable diseases (animal/plant pathogens and diseases, transmission, plant defences, specific/non-specific, preventing and treating) Flashcards
1
Q
What are bacteria?
A
- These are pathogens that cause communicable diseases
- They are prokaryotes, so they have a cell structure that is very different from the eukaryotic organisms they infect - they do not have a membrane-bound nucleus or organelles
- They can be classified in two ways: by their basic shape (rod, spherical, comma, spiralled, corkscrew), or by their cell walls
- Their are two main types of bacterial cell walls, which have different structures, and so react differently with a process called Gram staining - Gram-positive look purple-blue under the light microscope (e.g. MRSA), whereas Gram-negative appear red (e.g. E.coli)
2
Q
What are viruses?
A
- Non-living infectious agents
- 0.02-0.3μm in diameter
- Basic structure = some genetic material (DNA or RNA) surrounded by protein
- They invade living cells, where the genetic material of the virus takes over the biochemistry of the host cell to make more viruses
- They reproduce rapidly and evolve by developing adaptations to their host
- Bacteriophages = viruses that attack bacteria, another pathogen
3
Q
What are protoctista?
A
- A group of eukaryotic organisms with a variety of feeding methods - they include single-celled organisms and cells grouped into colonies
- A small percentage act as pathogens, causing communicable diseases in both plants and animals
- These are parasitic - this means they use people or animals as a host organism
- They may need a vector to transfer them to their hosts (e.g. mosquitoes in malaria) or they may enter the body directly through polluted water (e.g. amoebic dysentery and Giardia)
4
Q
What are fungi?
A
- Eukaryotic organisms that are often multicellular, although the yeasts which cause human diseases such as thrush are single-celled
- Can cause devastation in plants - fungi affect the leaves of a plant and stop them from photosynthesising, quickly killing the plant
- They cannot photosynthesise and digest their food extracellularly before absorbing the nutrients
- Many are saprophytes - this means that they feed on the dead and decaying matter
- Some are parasitic - this means they feed on living plants and animals
- When they reproduce, they produce millions of tiny spores which can spread huge distances - this adaptation means they can spread quickly and widely through crop plants
5
Q
How may different pathogens damage the host tissues directly?
A
- Viruses take over the cell metabolism - the viral genetic material gets into the host cell and is inserted into the host DNA. The virus then uses the host cell to make new viruses which then burst out of the cell, destroying it and then spread to infect other cells
- Some protoctista also take over the cells and break them open as the new generation emerge, but they don’t take over the genetic material of the host cell, rather they digest and use the cell contents as they reproduce
- Fungi digest living cells and destroy them
6
Q
How may different pathogens produce toxins which damage host tissues?
A
- Most bacteria produce toxins that poison or damage the host cells in some way, causing disease. Some damage the host cells by breaking down the cell membranes, some damage or inactivate enzymes and some interfere with the host cell genetic material so that the cells cannot divide
- Some fungi produce toxins which affect the host cells and cause disease
7
Q
Why do plant diseases threaten people?
A
- When crop plants fail, people have no food, especially in LEDCs where grains are staple foods
- It can also lead to economies struggling and a loss of jobs
8
Q
What is ring rot?
A
- A bacterial disease that affects potatoes, tomatoes and aubergines
- It is caused by the Gram-positive bacterium 𝘊𝘭𝘢𝘷𝘪𝘣𝘢𝘤𝘵𝘦𝘳 𝘮𝘪𝘤𝘩𝘪𝘨𝘢𝘯𝘦𝘯𝘴𝘪𝘴
- It damages leaves, tubers and fruit
- It can destroy up to 80% of the crop and there is no cure
- Once ring rot affects a field, it cannot be used as agricultural land for crop growing (specifically potatoes) for at least two years
9
Q
What is the tobacco mosaic virus (TMV)?
A
- A virus that infects tobacco plants and around 150 other species including tomatoes, peppers, cucumbers, petunias and delphiniums
- It damages leaves, flowers and fruit, stunting growth and reducing yields, and can lead to an almost total crop loss
- Resistant crop strains are available, but their is no cure
10
Q
What is Potato blight (tomato blight, late blight)?
A
- Caused by the protoctista 𝘗𝘩𝘺𝘵𝘰𝘱𝘩𝘵𝘩𝘰𝘳𝘢 𝘪𝘯𝘧𝘦𝘴𝘵𝘢𝘯𝘴, which is fungus-like
- The hyphae penetrate host cells, destroying leaves, tubers and fruit, causing millions of pounds worth of crop damage each year
- There is no cure but resistant strains, careful management and chemical treatments can reduce infection risk
11
Q
What is black sigatoka?
A
- This is a banana disease caused by the fungus 𝘔𝘺𝘤𝘰𝘴𝘱𝘩𝘢𝘦𝘳𝘦𝘭𝘭𝘢 𝘧𝘪𝘫𝘪𝘦𝘯𝘴𝘪𝘴, which attacks and destroys the leaves
- The hyphae penetrate and digest the cells, turning the leaves black
- If plants are infected it can cause a 50% reduction in yield
- Resistant strains are being developed - good husbandry and fungicide (a chemical that kills fungi) treatment can control the spread of the disease but there is no cure
12
Q
Why is black sigatoka such a big issue?
A
- Bananas are a staple crop, so this disease threatens food security
- Bananas are grown in over 130 countries where they are important both as a food crop and economically as a cash crop
- They are the 4th most important crop in the developing world
- In East Africa bananas are the staple food for around 50% of the population, with people eating about 400kg per year
- 90% of the bananas cultivated are produced on small farms and eaten locally. In recent years, black sigatoka has led to a 40% decrease in banana yields
- Around 10% of bananas are produced on big plantations for Western supermarkets. All these bananas are of the same variety, a clone called Cavendish (so, they’re genetically similar). Black sigatoka is invading these plantations too
13
Q
What is tuberculosis (TB)?
A
- A bacterial disease of humans, cows, pigs, badgers, and deer commonly caused by 𝘔𝘺𝘤𝘰𝘣𝘢𝘤𝘵𝘦𝘳𝘪𝘶𝘮 𝘵𝘶𝘣𝘦𝘳𝘤𝘶𝘭𝘰𝘴𝘪𝘴 and 𝘔. 𝘣𝘰𝘷𝘪𝘴
- It damages lung tissue and suppresses the immune system, so the body is less able to fight off other diseases
- In 2012, around 8.6 million people had TB worldwide, of which 1.3 million died
- People affected by HIV/AIDS are much more likely to develop TB infections
- In 2013, almost 33,000 UK cattle were killed because they were infected with bovine TB
- In people, TB is curable, via antibiotics, and preventable, by improving living standards and vaccination
14
Q
What is bacterial meningitis?
A
- A bacterial infection caused by 𝘚𝘵𝘳𝘦𝘱𝘵𝘰𝘤𝘰𝘤𝘤𝘶𝘴 𝘱𝘯𝘦𝘶𝘮𝘰𝘯𝘪𝘢𝘦 or 𝘕𝘦𝘪𝘴𝘴𝘦𝘳𝘪𝘢 𝘮𝘦𝘯𝘪𝘯𝘨𝘪𝘵𝘪𝘥𝘪𝘴
- It affects the meninges of the brain - these are protective membranes on the surface of the brain - and can spread to the rest of the body, causing septicaemia (blood poisoning) and rapid death
- It mainly affects very young children and teenagers aged 15-19
- A symptom of septicaemia = a blotchy red/purple rash that does not disappear when a glass is pressed against it, requires immediate medical treatment
- About 10% infected will die
- Up to 25% who recover have some permanent damage
- If delivered early, antibiotics can cure the disease
- Vaccines can protect against some forms of bacterial meningitis
15
Q
What is HIV/AIDS?
A
- Caused by a virus, which targets T helper cells in the immune system of the body
- It gradually destroys the immune system so affected people are open to other infections, such as TB and pneumonia, as well as some types of cancer
- HIV is a retrovirus with RNA as its genetic material
- There is no vaccine or cure, but there are many anti-retroviral drugs that are able to slow the progress of the disease to give many years of healthy life
