4.1.1 communicable diseases Flashcards
what are the different types of pathogens that cause communicable diseases?
bacteria
fungi
viruses
protoctista
bacteria
- Can be classified by their cell walls – the two main types of bacterial cell walls have different structures and react differently with gram staining
-> Gram positive bacteria – looks purple-blue under light microscope e.g. MRSA
-> Gram negative bacteria – appears red e.g. E.coli - Gram staining is useful because the type of cell wall affects how bacteria reacts to different antibiotics
- Are prokaryotes – do not have a membrane-bound nucleus or organelles
- can be classified by their basic shape e.g. bacillus (rod), coccus (spherical) etc
examples of bacteria
tuberculosis (TB)
bacterial meningitis
ring rot (potatoes, tomatoes)
virus
- non-living infections agents
- 0.02-0.3um in diameter
- 50x smaller in length than bacterium
- basic structure: some genetic material surrounded by protein
- Some viruses attack bacteria – these are called bacteriophages
- They take over the bacterial cells and use them to replicate, destroying the bacteria at the same time
- Bacteriophages are used to identify and treat diseases
- Very important in scientific research
- All naturally-occurring viruses are pathogenic
- Viruses invade living cells, where the genetic material of the virus takes over the biochemistry of the host cell to make more viruses.
- Reproduce rapidly and evolve by developing adaptations to their host, which makes them very successful pathogens
examples of viruses
HIV/AIDS (humans)
influenza (animals)
Tobacco Mosaic Virus (plants)
protoctista
- Group of eukaryotic organisms with a wide variety of feeding methods
- Include single-celled organisms and cells grouped into colonies
- A small percentage of Protoctista act as pathogens, causing devastating communicable diseases in both animals and plants
- Protists which cause disease are parasitic – use people or animals as their host organisms
-> May need a vector to transfer them to their hosts – e.g. malaria
-> May enter the body directly through polluted water – e.g. amoebic dysentery
examples of protoctista
malaria
potato/tomato late blight
fungi
- Fungal diseases can cause devastation in plants
- Fungal diseases of plants cause hardship and even starvation in many countries
- Eukaryotic organisms that are often multicellular, although the yeasts which cause human disease e.g. thrush are single-celled
- Cannot photosynthesis - digest their good extracellularly before absorbing the nutrients
- Many fungi are saprophytes – they feed on dead and decaying matter
- When fungi reproduce they produce millions of tiny spores which can spread huge distances, this adaptation means they can spread rapidly and widely through crop plants
- Some fungi are parasitic – feeding on living plants and animals
These are what cause communicable diseases
-> Fungal infections often affect the leaves of plants, they stop them photosynthesizing and so kill the plant
examples of fungi
black sigatoka (bananas)
ringworm (cattle)
athlete’s foot (humans)
how do viruses damage the host tissue directly?
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 burst out of the cell, destroying it and spreading to infect other cells
how do protoctista damage the host tissue directly?
Protoctista take over cells and break them open as the new generation emerge but do not take over genetic material
They digest and use cell contents as they reproduce
how do fungi damage the host tissue directly?
Fungi digest living cells and destroy them
Response of the body to the damage caused by the fungus gives the symptoms of disease
how does fungi produce toxins to damage the host tissue?
Fungi produce toxins which affect the host cells and cause disease
how does bacteria produce toxins to damage the host tissue?
Bacteria produce toxins that damage the host cell, causing disease
Some bacterial toxins damage the cell by breaking down the cell membranes, or inactivate enzymes or interfere with the host cell genetic material so the cells cannot divide
These toxins are a by-product of the normal functioning of bacteria
direct transmission of pathogens in animals
direct contact
inoculation
ingestion
direct transmission of pathogens in animals: direct contact
- kissing or contact with bodily fluids of another person e.g. bacterial meningitis, STDs
- direct skin-to-skin contact e.g. ringworm, athlete’s foot
- microorganisms from faeces transmitted on the hands e.g. diarrheal diseases
direct transmission of pathogens in animals: inoculation
- through a puncture wound or through sharing needles e.g. septicaemia
- from an animal bite e.g. rabies
- through a break in skin e.g. during sex (HIV/AIDS)
direction transmission of pathogens in animals: ingestion
- taking in contaminated food or drink or transferring pathogens to the mouth from the hands e.g. amoebic dysentery, diarrhoeal diseases
indirect transmission of pathogens in animals
fomites
vectors
droplet infection (inhalation)
indirect transmission of pathogens in animals: fomites
- inanimate objects such as bedding, socks or cosmetics can transfer pathogens e.g. athlete’s foot, gas gangrene and Staphlycoccus infections
indirect transmission of pathogens in animals: vectors
- transmits communicable pathogens from one host to another
- water e.g. diarrhoeal diseases
- animals e.g. mosquitoes transmit malaria, rat fleas transmit bubonic plague, dogs transmit rabies
indirect transmission of pathogens in animals: droplet infection
- minute droplets of saliva and mucus are expelled from mouth when talking, coughing and sneezing - may contain pathogens that can be breathed in e.g. influenza, tuberculosis
indirect transmission of pathogens in plants
soil contamination
vectors
indirect transmission of pathogens in plants: soil contamination
- Some pathogens can survive the composting process so the infection cycle can be completed when contaminated compost is used
- Infected plants often leave pathogens or reproductive spores from Protoctista or fungi in the soil – can infect the next crop – e.g. black sigatoka spores, ring rot bacteria, spores of P. infestans and TMV
indirect transmission of pathogens in plants: vectors
- Wind – bacteria, viruses and fungal or oomycete spores may be carried on the wind – e.g. Black sigatoka and P. infestans
- Water – spores swim in the surface film of water on leaves; raindrop splashes carry pathogens and spores – e.g. spores of P. infestans
- ## 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 in tobacco products, ring rot survives on farm machinery, potato sacks etc
indirect transmission of pathogens in plants: vectors
- Wind – bacteria, viruses and fungal or oomycete spores may be carried on the wind – e.g. Black sigatoka and P. infestans
- Water – spores swim in the surface film of water on leaves; raindrop splashes carry pathogens and spores – e.g. spores of P. infestans
- 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 in tobacco products, ring rot survives on farm machinery, potato sacks etc
- Animals – insects and birds carry pathogens and spores from one plant to another as they feed e.g. insects such as aphids inoculate pathogens directly into plant tissue
factors affecting the transmission of communicable diseases in animals
- Poor disposal of waste, providing breeding sites for vectors
- A compromised immune system including having HIV/AIDS or needing immunosuppressant drugs after transplant surgery
- Overcrowded living and working conditions
- Poor nutrition
- Climate change – can introduce new vectors and diseases e.g. increases temperatures promote the spread of malaria as the vector mosquito species is able to survive over a wider area
- Socioeconomic factors – for example, lack of trained health workers and insufficient public warning when there is an outbreak of disease can also affect transmission rates.
- Culture and infrastructure – in many countries traditional medical practices can increase transmission
factors affecting the transmission of communicable diseases in plants
- 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
- Planting varieties of crops that are susceptible to disease
- Damp, warm conditions increase the survival and spread of pathogens and spores
- Poor mineral nutrition reduces resistance of plants
- Over-crowding increases the likelihood to contact
what kind of disease is ringrot?
bacterial - caused by the gram positive bacterium Clavibacter michiganenis
what plants does ring rot affect?
potatoes, tomatoes, aubergines
what parts of the plant does ring rot damage?
leaves, tubers, fruit
what is the impact of ring rot?
Can destroy up to 80% of the crop
No cure
Once a field is infected it cannot be used to grow potatoes for at least 2 years
what kind of disease is TMV?
virus
what plants does TMV affect?
tobacco plants and 150 other species e.g. tomatoes, peppers, cucumbers, petunias and delphiniums
what parts of the plant does TMV damage?
leaves, flowers and fruit
what is the impact of TMV?
Stunts growth
Reduces yield
Leads to almost total crop loss
Resistant crop strains are available
No cure
what kind of disease is potato blight?
fungus-like protoctist oomycete
Phytophthora infestans
what plants does potato blight affect?
Hyphae penetrate host cells
potatoes, tomatoes
what parts of the plant does potato blight damage?
leaves, tubers and fruit
what is the impact of potato blight?
Crop damage
No cure
Resistant strains, careful management and chemical treatments can reduce infection risk