Communicable Diseases: transmission of diseases Flashcards
Why is finding how diseases are transmissible helpful?
Allows us to work out ways to reduce or prevent the disease spreading. There is direct and indirect transmission.
Describe direct contact (direct)
Kissing or any contact with body fluids of another person. e.g bacterial meningitis or HIV.
Direct skin-to-skin contact e.g. ring worm or athletes foot.
Microorganisms from faeces transmitted on the hands e.g. diarrhoeal diseases.
Describe inoculation (direct)
Break in the skin e.g. HIV
Animal bite e.g. rabies
Puncture wound or sharing needles e.g. septicaemia
Describe ingestion (direct)
Consuming contaminated food or drink, or transferring pathogen to the mouth from hands, e.g. amoebic dysentery.
Describe fomites (indirect)
Inanimate objects like bedding, socks or cosmetics.
e.g. athletes foot, gas gangrene, Staphylococcus.
Describe droplet infection - inhalation (indirect)
Minute droplets from saliva and mucus expelled from the mouth as you talk, cough or sneeze. When inhaled by others they can become infected, e.g. TB or influenza.
Describe vectors (indirect) humans
Transmit pathogens from one individual to another. Often animals but not always, e.g. mosquitos, rats, dogs, foxes, and bats. Water can also transmit.
Transmission between animals and humans
Bird flu strain H1N1 and brucellosis from sheep to humans. Reduced by minimising close contact and washing hands. Humans can be vectors for animal disease e.g. foot-and-mouth.
What factors affect the transmission of diseases?
Overcrowded living and working conditions.
Poor nutrition.
Compromised immune system like HIV or AIDS, or need for immunosuppressant drugs after transplants.
Poor disposal of waste - growth of vectors.
Climate change - new vectors and new diseases e.g. malaria.
Culture and infrastructure - traditional medical practises.
Socio-economic - lacked of trained health workers and insufficient public warning when there is an outbreak.
Direct transmission in plants
Involves direct contact of a healthy plant with a diseased plant e.g. ring rot, tobacco mosaic virus, blight and black sigatoka.
Describe soil contamination (indirect)
Infected plants leave pathogens or reproductive spores from protoctista or fungi in the soil.
Infect the next crop. e.g. ring rot, black sigatoka.
Some pathogens can survive composting process so infection cycle can be completed using contaminated compost.
Describe vectors (indirect)
Wind: pathogens can be carried on the wind e.g. black sigatoka between Caribbean islands.
Water: spores swim on the surface film of water on leaves. Raindrop splashes carry pathogens and spores e.g. potato blight.
Animals: insects and birds carry pathogens as they feed. Aphids inoculate directly into plant tissue.
Humans: hands, clothing, fomites, farming practises and transport around the world. e.g. TMV and ring rot.
Factors affecting transmission in plants
Planting varieties susceptible to disease.
Over-crowding - more contact.
Poor mineral nutrition reduces resistance.
Damp, warm conditions increase survival of pathogens.
Climate change - more wind and rainfall spread, and animal migration as warmer temps.
How to prevent spread in plants?
Leave plenty of room between plants.
Clear fields thoroughly.
Rotate crops - spores will die as no access to host.
Strict hygiene practises - washing hands, boots, sterilising storage sacks, washing machinery.
Control insect vectors.
