pathogens and disease Flashcards
infectious disease
disease resulting from infection of a host
organism by a pathogen, disease causing pathogen
Viruses
non-living
50 times smaller than the
average bacterium
Use host cells to reproduce rapidly and evolve by developing adaptations to their host
pathogenic to organisms
Protein coat(surface proteins) is how they can be identified
Unable to replicate outside of a host cell <– require the host cell machinery (DNA, ribosomes) for protein synthesis (do not have their own)
virus replication
virus attach to specific host cell
genetic material from virus injected into host cell
uses replication machinery of host cell
host cell spilts open releasing new virus
Bacteria
Prokaryotes
Do not have membrane-bound nucleus or organisms
Can be spherical, rod-shaped, corkscrew in shape
Have a cell wall (not cellulose)
Protista
Eukaryotic organisms
Incl single-celled organisms + cells that live in colonies
Small group of protista act as pathogens –> parasites ;use host organism for their benefit; might cause host cell to die
Many require a vector to transfer to their hosts; e.g. mosquito for malaria
May enter body directly through water;e.g. amoebic dysentery
Fungi
ive in the skin of an animal and its hyphae –> form a mycelium, grow under the skin surface
Reproductive hyphae grow to the surface of the skin to release spores –> redness and irritation
Fungal diseases are not a major problem in animals but can cause devastation in plants
Eukaryotic organisms – multicellular (although yeasts–> cause disease such as thrush –> single-celled
Cannot photosynthesise –> must digest their food extracellularly before absorbing nutrients
Saprophytes –> feed on dead and decaying matter
How do pathogens cause disease?
Damaging host cells or tissues directly
Producing toxins which damage host tissues
- exotoxins --> produced and secreted by a normal pathogen - endotoxins --> produced when a pathogen is damaged, and toxins are released
Two types of disease transmission
Direct
Indirect
Direct transmission
Pathogen/disease is transmitted directly from one organism to another
Direct contact between individuals e.g. sexual intercourse, touching an infected individual
Droplet infection e.g. sneezing/coughing tiny droplets of mucus/saliva directly onto someone
Inoculation – a break in the skin e.g. sharing needles, animal bite
Ingestion – consuming contaminated food/drink e.g. diarrhoeal diseases
Reduce risks of direct transmission
Washing hands regularly
Keeping surfaces clean
Cleaning & disinfecting cuts
Sterilising surgical instruments
Using condoms
Indirect transmission
When a disease is transmitted from one organisms to another via an intermediate
Fomites – inanimate objects can harbour & transfer pathogens e.g. bedding, cosmetics, clothing
Vectors – an organism that spreads disease by carrying pathogens from one host to another but its unaffected e.g. mosquito carrying malaria parasite
factors affecting disease transmission
Living conditions :
Overcrowded living and working conditions increase transmission
Poor nutrition
Poor disposal of waste which provides breeding road for vectors
Social factors :
Culture and infrastructure – in some countries, traditional medical practices can increase transmission
Socioeconomic factors e.g. a lack of trained health workers, insufficient education of the public
Climate :
Climate change – new vectors and diseases can energy; spread of malaria can be promoted as temperature rise
Fungi in plants
Fungi often lives in the vascular tissue of plants –> to acquire nutrients
The hyphae release extracellular enzymes, e.g. cellulases to digest the surrounding tissue –> decay
Leaves will often become mottled in colour and shrivel before dying, halts photosynthesis
How is a crop yield reduced?
Fungal infection causes mottling & discolouration
Photosynthesis is reduced
Less carbohydrate is produced
Plants are smaller, fruit is smaller
Yield is reduced
Pathogens can reduce plant growth and yield
Reducing the rate of photosynthesis (blocking light or destroying chloroplasts)
Increasing the rate of respiration as the plant fights the infection
Feeding on plant’s sugars
Plant may lose water through wounds
Pathogens can block xylem and phloem
Factors affecting the transmission of diseases in plants
The planting of crops that are susceptible to disease
Over-crowding of plants so that physical contact is more likely
Poor mineral content of soil reduces plant resistance to disease
Damp, warm conditions increase the survival and spread of pathogens and spores
Climate change : increased rainfall & wind promote the spread of diseases; changing conditions allow animal vectors to enter new areas and spread pathogens; drier conditions may reduce the spread of disease
Preventionof transmission of diseases in plants
Leave plenty of space between the plants to minimise contact
Clear fields thoroughly after harvesting
Rotate crops
Follow strict hygiene procedures – washing hands and boots, sterilsing storage sacks, washing down machinery
Control insect vectors
