12 - Communicable Diseases Flashcards
What parts of the plant does Ring Rot damage?
Leaves, tubers and fruit
What causes a communicable disease?
A pathogen
What are the 4 main types of pathogen?
- Bacteria 2. Viruses 3. Protoctista 4. Fungi
What does a vector do?
Carry pathogens from one organism to the other
How are communicable diseases in plants spread?
Directly plant-to-plant
What proportion of bacteria cause communicable disease?
Only a small proportion
What are the two main ways bacteria are classified?
- By shape 2. By cell wall
What shape are bacilli?
Rod-shaped
What is chain of bacilli bacteria called?
Strepto-species type i.e. Streptobacilli
What is a cluster of cocci bacteria called?
Staphylo-species type i.e. staphylococci
What shape is a vibrios?
Comma shaped
What is a corkscrew-shaped bacterium called?
Spirochaetes
What shape is a coccus?
Spherical
What are the two types of bacterial cell wall?
Gram-positive and gram-negative
What colour do gram-positive bacteria go with gram staining?
Purple-blue
What colour do gram-negative bacteria go with gram staining?
Red
What are some features of a gram-positive cell wall (excluding colour with gram staining)
Thicker but less tough, more susceptible to antibiotics which damage the cell wall, more peptidoglycan, lower lipid content, more prominent mesosome
What makes a gram-positive cell wall go purple-blue with gram staining?
The peptidoglycan in their cell wall retains crystal violet stain
What are some features of a gram-negitive cell wall (excluding colour with gram staining)?
Thinner but tougher, higher lipid content due to outer cell membrane, less susceptible to antibiotics
What is an example of a bacterium with a gram-positive cell wall?
MRSA
What is an example of a bacterium with a gram-negative cell wall?
E.coli
What is a bacterial cell wall mostly made up of?
Peptidoglycan
What is the structure of peptidoglycan?
Massive disaccharide polymers cross-linked by short chains of identical amino acid monomers
What is the basic structure of any virus?
Some genetic material (either DNA or RNA) surrounded by a protective protein coat
What is the mechanism of infection of a virus?
They attach to the cell and inject their genetic material, which takes over the biochemistry of the host cell to make more viruses by inserting itself into the host DNA, until so many are made that the host cell is lysed (bursts) and the new viruses are released
What 2 things make viruses very successful pathogens?
They reproduce rapidly and evolve by developing adaptations to their host
What proportion of naturally occurring viruses are pathogenic?
All of them
How many other types of organism do viruses infect?
Every other type of organism, including other viruses
What is a bacteriophage?
A virus which attacks a bacteria
What is a virophage? Give an example
A virus which infects other viruses, such as the Sputnik virus
Are protoctista eukaryotic or prokaryotic?
Eukaryotic, with a wide variety of feeding methods
What proportion of protoctista are pathogenic?
Only a small percentage, most are harmless
What are fungi a major problem for?
Some plants- they tend not to be a major problem for animals
Are fungi eukaryotic or prokaryotic?
Eukaryotic
Are protoctista unicellular or multicellular?
Unicellular, although they can group into colonies
Are fungi unicellular or multicellular?
Usually multicellular, with the exception of yeasts
How do fungi feed?
Many are saprophytes, but the pathogenic ones are parasites and eat living organisms. They can’t photosynthesise, so digest food outside of their cells before absorbing the nutrients
What do saprophytes feed on?
Dead and decaying matter
What part of a plant do many plant fungal diseases affect?
The leaves, stopping the plant photosynthesising and killing it rapidly
How do fungi reproduce?
They produce millions of spores, which can spread huge distances and spread their disease quickly among crops
What organelles does yeast have?
Nucleus, mitochondria, cell membrane and a permanent vacuole
Apart from yeast organelles, what organelles may a more complex fungus have?
A cell wall (and vesicles) and food storage granules of starch
What are the two main pathogenic modes of action?
- Damaging host tissue directly 2. Producing toxins which damage host tissue
What is the mechanism of infection of fungi?
They digest and destroy living cells. This, combined with the response of the body to the damage caused by the fungus, causes the disease
What is the mechanism of action of protoctista which damage host tissue directly?
They take over cells and lyse them as a new generation emerge, but do not take over the genetic material of the cell like a virus; instead, they digest and use the cell contents as they reproduce
Apart from bacteria, what type of pathogen can produce cytotoxins?
Fungi
Are bacterial toxins produced deliberately to damage the host?
No, they are a by-product of the natural function of the bacterial cell
What is the mechanism of action of most pathogenic bacteria?
They produce toxins which poison/damage the host cells in some way
What are 3 ways bacterial toxins can damage cells?
- Breaking down cell membranes 2. Damaging/deactivating enzymes 3. Interfering with the host DNA so the cell can’t replicate
What organisms does tuberculosis affect?
Humans, cows, pigs, badgers and deer
What type of pathogen is tuberculosis caused by?
Bacteria
People suffering from what other disease are more likely to suffer from tuberculosis?
HIV/AIDS
How is TB cured and prevented?
Cured with antibiotics, prevented by vaccination or better living standards
How is TB spread in humans?
Droplet infection
What is the mechanism of TB?
It damages and destroys lung tissue and suppresses the immune system so that the body is less able to fight off other diseases
How is bacterial meningitis spread?
By droplet infection
How is bacterial meningitis cured and prevented?
Curable with antibiotics if administered early enough, vaccines can protect against some forms
What are the mechanism and symptoms of bacterial meningitis?
Infection of the meninges (protective membranes on brain surface) which can spread to the rest of the body and cause fatal septicaemia. Symptoms vary depending on type of bacteria, but all share a blotchy red/purple non-blanching rash
Who are the main groups affected by bacterial meningitis?
Very young babies and 15-19 year olds
What is the mechanism of the HIV virus?
It attacks T helper cells, which gradually destroys the immune system and leaves sufferers vulnerable to secondary infection
What type of virus is HIV/AIDS?
A retrovirus
How does a retrovirus work?
A virus that is composed not of DNA but of RNA. Retroviruses have an enzyme, called reverse transcriptase, that gives them the unique property of transcribing their RNA into DNA after entering a cell. The retroviral DNA can then integrate into the chromosomal DNA of the host cell, to be expressed there.
What animals does bacterial meningitis affect?
Humans
What animals does HIV/AIDS affect?
Humans and some other primates
How is HIV spread?
Passed between people via infected bodily fluids i.e. via unprotected sex, shared needles, contaminated blood and mother to baby through either pregnancy or breastfeeding. FGM also increases its spread if equipment is reused
How is HIV cured?
No vaccine or cure but antiretroviral drugs can slow its progress
What animals does influenza affect?
Mammals and birds
What is the mechanism of influenza?
Infects ciliated epithelial cells in the gas exchange system, killing them and leaving the airways vulnerable to secondary infections such as bacterial pneumonia
What are the 3 types of influenza and which is most virulent?
A,B,C, with A being most virulent
Why is a vaccine made each year for flu?
Because flu viruses undergo small, regular mutations, so their surface antigens are constantly being reshuffled
Is the a cure for flu?
No
What is zoonosis and give an example of something that does it?
Where a disease can spread from animals to humans. An example would be influenza (swine flu or bird flu)
What causes malaria?
Several species of protoctista from the genus Plasmodium, with the most common being Plasmodium Falciparum, spread by the bite of the female Anopheles mosquito
What is the mechanism of malaria?
Infects red blood cells, liver, brain. Disease recurs, making people weak and vulnerable to secondary infection
What is the cure for malaria?
No vaccine and limited cures such as quinine, but preventative measures such as vector control through mosquito nets etc. can be very effective
What are 2 reasons malaria can be difficult to treat?
- Protoctista ‘hides’ inside red blood cells 2. Caused by several different species so surface antigens may be different
What causes ringworm?
Fungi, with different fungi affecting different species.
What is a cure for ringworm or Athlete’s Foot?
Antifungal creams
What are the symptoms of ringworm?
Grey-white, crusty, infectious circular area of skin which aren’t damaging but are unsightly and itchy
What causes Athlete’s Foot?
Tinia Pedia, a form of human ringworm fungus
Where does the Athlete’s Foot fungus typically grow?
The warm, moist skin between toes, which it digests
What are the symptoms of Athlete’s Foot?
Cracking and scaling which is itchy and may become sore
What animals does ringworm affect?
Mammals
What plants does Ring Rot affect?
Potatoes, tomatoes and aubergines
What is the cure for Ring Rot?
There is none
What happens to a field once it has been infected by Ring Rot?
It cannot be used to grow potatoes, tomatoes or aubergines for at least 2 years
What type of pathogen causes Ring Rot?
A bacterium
What does TMV infect?
Tobacco plants and 150 other species
How is TMV prevented and cured?
Resistant crop strains can prevent it but there is no cure
What is the mechanism of TMV?
Damages leaves, flowers and fruit, stunting growth and reducing yield, and can leads to almost total crop loss
What is Potato late blight caused by?
A fungus-like protoctista called an oomycete
How is Potato late blight prevented and cured?
No cure but can be prevented via use of resistant strains, careful management and chemical treatments
What is the mechanism of Potato late blight?
Hyphae penetrate host cells and destroy leaves, tubers and fruit, leading to millions of pounds of crop damage per year
What type of pathogen causes Black Sigatoka?
A fungus
What type of plant does Black Sigatoka affect?
Bananas
What part of the plant does Black Sigatoka affect?
The leaves
What is the mechanism of Black Sigatoka?
Hyphae penetrate and digest cells, turning leaves black. Can cause 50% reduction in yield of infected plants
How is Black Sigatoka cured and prevented?
No cure but resistant strains being developed and good husbandry and fungicide treatment can control the spread of the disease
What are the two main types of transmission of communicable diseases between animals?
Direct and indirect
What are the three main types of direct transmission in animals?
- Inoculation 2. Direct contact 3. Ingestion
What happens in ingestion in the direct transmission of animal pathogens?
Contaminated food of drink are ingested or pathogens are transferred from the hands to the mouth
What are two examples of diseases spread by ingestion?
- Amoebic dysentery 2. Diarrhoeal diseases
What are 3 ways pathogens can be spread via inoculation?
- Animal bite i.e. rabies 2. Break in the skin i.e. unprotected sex 3. Puncture wound or shared needles i.e. septicaemia
What are 3 ways pathogens can be spread via direct contact?
- Direct skin-to-skin contact i.e. ringworm, athlete’s foot 2. Kissing or any contact with another person’s bodily fluids i.e. many STDs or bacterial meningitis 3. Microorganisms from the faeces transmitted on the hands i.e. many diarrhoeal diseases
What are the 3 main types of indirect transmission of pathogens between animals?
- Formites 2. Vectors 3. Droplet infection
What is a formite infection?
Where an inanimate object such as socks, bedding or cosmetics can transfer pathogens
What are 3 types of pathogen spread by formite infection?
- Gas gangrene 2. Athlete’s foot 3. Staphylococcus infections
What occurs during a droplet infection?
Minute droplets of saliva or mucus are expelled from the mouth during talking, coughing or sneezing; if the droplets contain pathogens, anyone who inhales them may contract the illness
What are two types of disease which can be spread by droplet infection?
TB or influenza
What are the most common types of vector to spread diseases between animals?
Animals such as malaria-carrying mosquitoes, dogs, foxes and bats carrying rabies, fleas carrying the plague
What is a non-animal example of a vector (to spread diseases between animals)?
Water, which can transmit diarrhoeal diseases
What disease can be transmitted between sheep and humans?
Brucellosis
How can the risk of zoonotic infection be reduced?
Washing hands after any contact with animals
What are some factors which can increase the risk of transmission of diseases between animals?
- Poor nutrition 2. Overcrowded working and living conditions 3. A compromised immune system 4. Climate change, which can introduce new vectors and diseases to areas 5. In humans, poor disposal of waste provide a breeding grounds for vectors 6. Culture and infrastructure- in many countries, traditional practices can increase transmission 7. Socioeconomic factors such as a lack of trained health workers and insufficient public warning of outbreaks
Can plant pathogens be transmitted directly?
Yes, if a part of a healthy plant comes into direct contact with a part of an infected plant
What are some plant pathogens which can be transmitted directly?
Ring rot, TMV, black sigatoka, potato late blight
What are the two main types of indirect transmission of pathogens in plants?
- Soil contamination 2. Vectors
How are plant pathogens transmitted via soil contamination?
Infected plants often leave pathogens or spores from fungi/protoctista in the soil, which can infect the next crop. Some pathogens or their spores can also survive the composting process, so the contaminated compost can infect plants it is spread on
What are the 4 main types of vectors which spread plant pathogens?
- Wind 2. Water- spores swim in the film of surface water on leaves, and both spores and pathogens can be carried by raindrops 3. Animals- Insects and birds can carry pathogens and spores, and aphids can inoculate directly 4. Humans- Hands, clothing, fomites, farming practices and the transport of crops
What are some factors affecting the spread of communicable diseases between plants?
- Planting varieties of crops which are susceptible to disease 2. Overcrowding increasing the likelihood of contact 3. Poor mineral nutrition reducing plants’ resistance 4. Damp, warm conditions increasing the survival and spread of pathogens and spore 5. Climate change- increased rainfall and wind, new animal vectors, although drier conditions may reduce spread of disease
What are 3 things which act as physical barriers to pathogens in plants?
- Waxy cuticle of leaves 2. Bark on trees 3. Cellulose cell wall