Transmission of Pathogens

Question 1

Transmission of Pathogens

Answer 1

Pathogens have a life cycle that involves living and reproducing in/on a host.

Question 2

Indirect transmission

Answer 2

Indirect transmission: passing a pathogen from host to new host, via a vector.
Vector: an organism that carries a pathogen from one host to another. The pathogen has to be “inside” an organism for it to be a vector (doorknob isn’t a vector).

Question 3

Examples of indirect transmission :

Answer 3

Spores – carried in air/water (e.g. late blight) [fungi/protoctista use spores to reproduce].

Mosquitoes (female) – plasmodium protoctist parasite that causes malaria spread between humans via mosquitoes that feeds on blood, releasing plasmodium into bloodstream.

Droplet infection – if droplets are transported by air/waster/food to next organism (e.g. TB/influenza).

Question 4

Factors that affect human disease transmission:

Answer 4

• Overcrowding/poor ventilation – lots of people living together, diseases spread by droplet infection
  (TB), bacteria can remain in air for long periods of time and infect new people.
• Social Factors:
• Poor healthcare – people are less likely to be diagnosed and treated for HIV, less access to most effective anti-HIV drugs, so the virus is more likely to be passed on to others. May not be vaccinated for diseases like TB.
• Poor health education – to inform people about how HIV is transmitted and how it can be avoided (e.g. condoms) can reduce transmission.
• Poor health – particularly if person has HIV/AIDS as they are likely to contract other diseases.
• Homelessness/poverty/poor diet/poor sanitation.
• Climate – potato/tomato late blight common during wet summers as the spores need water to
  spread. Malaria common in humid tropical countries, ideal conditions for mosquitos to breed.
• Climate change/global warming means temperatures and rainfall increase.
  Bacteria/protoctists/fungi are able to grow/reproduce more rapidly in warm and moist climates, and many pathogens are killed by cold winters. As temperature increases these pathogens can survive in new areas.
• Behaviours – e.g. global travel, more sexual partners.

Question 5

Transmission of plant pathogens:

Answer 5

Direct:
- Pathogens in leaves are distributed when leaves are shed infecting the soil.
- Pathogens can also enter fruit/seeds, will then be distributed in the seeds to offspring.
- In monoculture, contact between infected plants and non-infected is easy.

Indirect:
- Pathogens in soil and enter plants roots – especially if roots are damaged by animals/replanting.
- Fungi produce spores as a means of asexual reproduction, which may be carried in the wind/water. - Insect vectors – spores or bacteria become attached to beetles which transmit it to the next plant. - Human vectors – transferred by hands.

Question 6

what is direct transmission

Answer 6

Direct transmission: passing a pathogen from host to new host, with no intermediary.

Question 7

Examples of direct transmission

Answer 7

Contact/touching
Sexual intercourse
Ingestion
Droplet infections

Question 8

Contact/touching

Answer 8

Contact/touching – of contaminated surfaces (soil) that harbour the pathogen or skin to skin. (e.g. bacterial meningitis, ringworm, athlete’s foot).
- Prevent by hygiene: Wash hands, clean/disinfect surfaces & cuts. Sterilising surgical instruments.

Question 9

Sexual intercourse

Answer 9

Sexual intercourse – HIV is transmitted though bodily fluids (blood).
- Don’t share dirty needles, condoms, transfusions, placenta/milk, sex.

Question 10

Ingestion

Answer 10

Ingestion – Eating food/drinking water that is contaminated by pathogen (e.g. cholera, food poisoning).

Question 11

Droplet infection

Answer 11

Droplet infection – cough/sneeze droplets of mucus/saliva directly into someone (e.g. TB/influenza).
- NOTE: droplet infection is indirect transmission if droplets transported to person in air/water.