4.1 - Communicable diseases Flashcards
What is disease?
A condition that impairs the normal functioning of an organism
Which types of organisms get diseases?
Animals and plants
What are communicable diseases?
- diseases that can be transferred from one infected organism to another
- can be the same or different species
- caused by pathogens
What is a host?
An organism in which a pathogen lives
What is a vector?
Carries a disease and spreads it
Eg water, insects
What is a pathogen?
An infectious microorganism that causes disease
What are the different types of host-pathogen interactions?
- mutualistic
- commensal
- parasitic
What is a mutualistic relationship?
- both organisms benefit
- eg bacteria in stomachs of domestic ruminants (bacteria digests cellulose for host, gets nutrition and environment)
What is a commensal relationship?
- where one species lives harmlessly on the body of a larger species
- eg microbial flora on skin, mouth etc
What is a parasitic relationship?
- only benefits the parasite
- some can become pathogenic if there are changes to a hosts health or if they infect an unnatural host (eg rabies virus)
What are the different types of pathogen?
- bacteria
- virus
- protoctista (Protista)
- fungi
What are bacteria?
- prokaryotes
- a small proportion of bacteria are pathogens
- will damage hosts by releasing waste products/toxins or by attacking the cells
How can bacteria be classified?
By their basic shapes
By cell walls:
- GRAM POSITIVE BACTERIA - look purple/blue under light microscope when Gram stained
- GRAM NEGATIVE BACTERIA - appear red under light microscope when Gram stained
Useful as cell wall affects how bacteria react to antibiotics
What are viruses?
- non-living pathogens
- 0.02-0.30 micrometers (50x smaller than typical bacteria)
- basic structure = genetic material (DNA or RNA) surrounded by protein coat
- cant reproduce without cells
- invade cells and take over genetic machinery/ biochemistry of host cell
- causes cell to manufacture more copies of the virus
- host cell eventually bursts, releasing many new viruses which infect healthy cells
- they reproduce rapidly and evolve by developing adaptations to host
- this makes them very successful pathogens
What are bacteriophages
- viruses that attack bacteria
- people use bacteriophages to identify and treat some diseases, making them important in scientific research
What are protoctista
- aka Protista
- eukaryotic organisms
- have a wide variety of feeding methods
- include single-called organisms and cells grouped into colonies
- a small percentage of protoctista act as pathogens, causing diseases in plants and animals
- usually cause harm by entering host cells and feeding on contents as they grow. Then they break open cell as new generation emerges
What are fungal parasites
- fungal diseases aren’t a major problem in animals but can be devestating for plants
- fungi are eukaryotic
- usually multicellular, but some unicellular (eg yeast)
- cant photosynthesise
- digest food extracellularly before absorbing nutrients
- many are saprophytes(feed on dead/decaying matter)
- some are parasitic - feed on living plants and animals (these are pathogenic)
- often affect leaves of plants, stopping them photosynthesising and killing them.
- when they reproduce they release millions of spores which can spread over crops, killing them.
- below surface of fungo there’s are fine filaments called hyphae, which together form mycelium
- fungal infections in animals involve mycelium growing under skin surface
- either digests living cells or produces toxins
Which diseases are caused by bacteria?
- tuberculosis (TB)
- bacterial meningitis
- ring rot
Which diseases are caused by viruses?
- HIV/AIDS
- Influenza
- tobacco mosaic virus (TMV)
Which diseases are caused by fungi?
- black sigatoka
- ringworm
- athletes foot
Which diseases are caused by protoctista?
- potato/tomato late blight
- malaria
What is tuberculosis (TB)?
- caused by bacteria: mycobacterium tuberculosis and M. bovis
- affects animals (typically humans and cattle)
- affects many parts of the body, killing cells and tissue
- lungs most often affected
- in ppl it’s both curable (antibiotics) and preventable (improving living standards and vaccination)
What’s bacterial meningitis?
- caused by bacteria: neisseria meningitidis or streptococcus pneumonia
- affects humans (very young children and teens 15-19)
- infection of the meninges (membranes that surround spinal cord and brain)
- membranes become swollen and may cause damage to brain and nerves
- can spread to the rest of the body causing septicaemia (blood poisoning) and death
- can be cured with antibiotics if delivered early, vaccines can protect against some forms of bacterial meningitis
What is ring rot?
- caused by bacteria by clavibacter michiganesis (gram positive)
- affects potatoes and tomatoes
- ring of decay in the vascular tissue of a potato tuber or tomato accompanied by leaf wilting
- damages leaves, tubers and fruit
- once it affects a field it cannot be used to grow potatoes again for at least 2 years
- no cure
What is HIV?
- caused by human immunodeficiency virus, HIV
- affects humans
- attacks cells in immune system and compromises the immune response, making people more open to other infections
- no cure rot vaccine, but anti-retroviral drugs slow process of disease
What is influenza?
- a viral infection caused by orthomyxoviridae
- attacks ciliates epithelium in gas exchange system
- affects animals, including humans
- causes respiratory problems, headaches and muscles
- can be fatal because it kills ciliates epithelium, leaving animal more vulnerable to secondary infections
- no cure, but vaccinations available
What is the tobacco mosaic virus (TBV)?
- viral infection caused by tobacco mosaic virus
- affects many different plants eg tobacco plants, tomatoes, pepper, cucumbers, petunia
- damages leaves (mottling and discolouration), flowers and fruit, stunting growth + reducing yield
- resistant crop strains available, but there is no cure
What is black Sigatoka?
- caused by fungus Mycosphaerella fijiensis
- affects banana plants
- attacks and destroys leaves: hyphae penetrate and digest the cells, turning leaf black
- can cause a 50% reduction in yield of plant
- resistant strains being developed
- good husbandry and fungicide treatment can control the spread
- no cure
What is ringworm?
- a fungal disease caused by trichophyton verrucosum
- affects mammals including cattle
- growth of fungus in skin with spores erupting through skin to cause grey-white rash
- cure = anti fungal cream
What is athletes foot?
- fungal disease caused by tibia pedia
- affects humans
- form of human ringworm, where fungus feeds on warm, moist skin between toes
- cure = anti fungal creams
What is malaria?
- caused by protoctista plasmodium
- spread by bites of infected mosquitos (vector)
- invades red blood cells, the liver, brain
- causes headache and fever, which can lead to coma and death
- no vaccine and limited cure
- can be prevented by controlling vector (mosquitos) with nets, long sleeves, etc
What is potato/tomato late blight?
- caused by protoctist oomycete phytophthora infestans
- hyphae penetrates hosts cells, destroying leaves, tubers and fruit
- no cure
- resistant strains, careful management and chemical treatments can reduce infections
How can diseases be directly transmitted between animals?
DIRECT CONTACT:
- kissing/ contact with bodily fluid eg in sex
- direct skin-to-skin contact eg athletes foot,
- microorganisms from faeces transmitted on hands eg diarrhoeal diseases
INOCULATION:
- through break in the skin eg during sex
- from animal bite eg rabies
- through puncture wound/ sharing needles eg septicaemia
DROPLET INFECTION (INHALATION)
- minute droplets are expelled from mouth when talking, coughing or sneezing
- if droplets fall directly onto another organism, it is direct transmission
- could be indirect if droplets are left in the air
How can diseases be indirectly transmitted between animals?
INGESTION:
- taking in contaminated food/drink
- transferring pathogens from mouth to hands
- eg amoebic dysentery, diarrhoael diseases
FOMITES:
- inanimate objects eg bedding, socks or cosmetics
- eg athletes foot, gas gangrene, staphylococcus infections
VECTORS:
- vectors transmit pathogens from one host to another
- mostly animals, eg malaria in mosquitos, plague in rats, rabies in dogs, foxes, bats
- water can be a vector eg diarrohoeal diseases
What are the factors affecting the transmition of communicable diseases in animals?
The probability of catching a communicable disease is increased by:
- overcrowding
- poor nutrition
- compromised immune system eg immunosuppressant drugs, HIV
- poor disposal of waste
- climate change eg higher temp = more mosquitos = promotes spread of malaria
- culture + infrastructure - traditional medicial practices can increase transmission in some countries
- socioeconomic factors - lack of trained health workers and insufficient public warnings of outbreak can increase rates
How are diseases directly transmitted between plants?
Direct contact of a healthy plant with and any part of a diseased plant
Eg ring rot, TMV, black Sigatoka, late tomato blight
How are diseases transmitted indirectly between plants?
SOIL CONTAMINATION:
- infected plants may leave bacteria and virus pathogens or reproductive spores from protoctista or fungi in soil
- these can affect the next crop
- some (mainly spores) can survive the composting process
VECTORS:
- wind: bacteria, viruses and fungal/oomycete spores can be carried through 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 from one plant to another as they feed, and may inoculate pathogens directly into plant tissue
- humans: pathogens + spores area transmitted through hands, clothing, fomites, farming practices and transport of crops around the world
What are the factors affecting the transmission of diseases in plants?
- planting crops which are susceptible to disease
- overcrowding increases likelihood of contact
- poor mineral nutrition reduces resistance of plants
- damp, warm conditions increase survival and spread of pathogens and spores
- climate change: increased rainfall and wind promote spread of diseases, changing conditions allows animal vectors to spread to new places. (However, during conditions may reduce the spread of disease)
What are the physical barriers that plants use to defend themselves against pathogens?
- waxy cuticle prevents pathogens coming into direct contact with epidermal cells
- bark contains lignin. it becomes rigid and woody by deposition of lignin in cell walls. Bark prevents pathogens from coming into direct contact with pathogens
- before a leaf falls off, fatty material is deposited, sealing off vascular bundles
- cellulose cell walls are a structural barrier made up of cross-linked cellulose fibres
How do pathogens get through physical barriers in plants?
- natural openings eg stomata
- mechanical damage (eg wounds, damage when animals feed on plants)
These allow pathogens to enter the plant and infect it.
How do plants recognise an attack?
- some molecules from the pathogen are recognised directly by the plant
- alternatively, when pathogenic enzymes breakdown the cell wall, the breakdown products are recognised
- signalling molecules alert the nucleus that the plant is under attack
- polysaccharides (cal lose and lignin) are made tho strengthen the cell walls
- defensive chemicals signal to the other cells that they are under attack
- some defensive molecules directly attack pathogens
What are the mechanical responses to infection in plants?
- guard cells close stomata
* callose is produced and deposited
What is callose?
A polysaccharide containing β-1,3 and β-1,6 glycosidic bonds between glucose monomers
Important in the pant response to infection
What does current research suggest the role of callose is in a plants response to infection?
- its a rapid, unspecific response to invasion by a pathogen
- callose is synthesised and deposited between the cell wall and cell membrane, as well as at the plasmodesmata to prevent the spread of pathogens to adjacent cells
- large amounts of callose and lignin are deposited in the cell walls to thicken and strengthen the cell wall, increasing the effectiveness of the mechanical barrier
- callose blocks sieve plates in phloem, sealing off infected cells and preventing spread of pathogens via the transport system
What is necrosis?
When injury activates intracellular enzymes in plants that kills cells near the suite fo infection.
This is to prevent pathogens from spreading
What are some examples of chemical defences against pathogens in plants?
INSECT REPELLENTS
•citronella (lemongrass)
• pine resin (pine trees)
INSECTICIDES • pyrethrin (chrysanthemums) • caffeine, mint, cinnamon • ricin (caster oil beans) • cyanide (even lethal to humans)
ANTI-FUNGAL • gossypol • phenols • saponins • chitinases
ANTIBACTERIAL • phenols • gossypol • defensins • lysozymes
ANTI-OOMYCETES
• glucanases
What are terpenoids?§
- range of essential oils that have antibacterial and anti-fungal properties
- may also create a scent
- eg menthols from mint
What are phenols?
- have antibacterial and antifungal properties
- tannins found in bark inhibit attack by insects (bind to salivary proteins and digestive enzymes like trypsin and chymotrypsin, deactivating enzymes)
What are alkaloids?
- nitrogen-containing compounds
- give bitter taste to inhibit insects from feeding
- act on metabolic reactions by either inhibiting or activating enzyme action.
- some inhibit protein synthesis
- eg caffeine, nicotine, cocaine, morphine, solanine
What are defensins?
- small cysteine-rich proteins that have broad anti-microbial activity
- act on small molecules in the plasma membrane of pathogens, inhibiting the action of ion transport channels
What are hydrolytic enzymes?
Found in spaces between cells
Include :
•chitinases (breaks down chitin I’m fungal cell walls)
• glucanases (hydrolyse glycosidic bonds in glucans)
•lysozymes (degrade bacterial cell walls)
What physical barriers prevent infection?
- skin is a tough keratin layer which prevents pathogens entering. produces sebum, an oily substance that inhibits pathogen growth
- blood clotting prevents pathogens from entering the skin through lesions
- hydrochloric acid in stomach kills bacteria.
- mucous membranes trap pathogens and may secrete anti microbial enzymes
What are expulsive reflexes?
When body attempts to force foreign substances out.
• irritation of mucous membranes in nostrils causes sneezing
• irritation of ciliated epithelium in respiratory tract causes coughing
• vomiting and diarrhoea expel contents of cut as well as infective pathogens
How do blood clots form?
When platelets come into contact with the collagen in skin or the wall of a da,aged blood vessel, they stick to it and start to secrete several substances.
The blood clot prevents pathogens from entering the wound.
What is thromboplastin?
Secreted by platelets when there is a wound.
Enzyme which triggers a cascade of reactions, resulting in a blood clot forming (thrombus)
