12.3 Transmission of communicable diseases

Question 1

What are the 2 main types of transmission?

Answer 1

Direct transmission

Indirect Transmission

Question 2

How is the pathogen spread in direct transmission?

Answer 2

The pathogen is transferred directly from one individual to another

Question 3

What are the 3 ways in which diseases are spread through direct transmission?

Answer 3

Direct contact
Inoculation
Ingestion

Question 4

How are diseases spread through ‘Direct Contact’?

Answer 4

• Kissing or any contact with bodily fluids of the infected person.
E.g. Bacterial meningitis + STDs

• Direct skin-skin contact
E.g. ring worm, athlete’s foot

• Microorganisms from faeces transmitted on hands
e.g. diarrhoeal diseases

Question 5

How are diseases spread through ‘Inoculation’?

Answer 5

• Through a break in skin
e.g. during sex, HIV
• From an animal bite
e.g. rabies
• Through a puncture wound / shared needles
e.g. septicemia

Question 6

How are diseases spread through ‘Ingestion’?

Answer 6

• Ingesting contaminated food / drink, or transferring pathogens from hands → mouth
e.g. amoebic dysentery, diarrhoeal diseases

Question 7

What is Indirect Transmission?

Answer 7

Where pathogens travel from one individual to another indirectly

Question 8

What are the 3 ways in which diseases are spread through indirect transmission?

Answer 8

Through:

1. Fomites
2. Inhaling infected droplets
3. Vectors

Question 9

How are diseases spread through ‘Fomites’?

Answer 9

• Inanimate objects such as bedding, socks or cosmetics can transfer pathogens
E.g. athlete’s foot, gas gangrene and Staphylococcus infections

Question 10

How are diseases spread through ‘Droplet Infection (inhalation)’?

Answer 10

Tiny droplets of saliva + mucus are expelled from your mouth as you talk, cough or sneeze.
If these droplets contain pathogens, healthy individuals who inhale these droplets could become infected.
E.g. influenza, TB

Question 11

How are diseases spread through ‘Vectors’?

Answer 11

Vectors transmit communicable pathogens from one host to another.
Vectors are often animals, but not always:
E.g.
• Mosquitoes transmit malaria
• Rat fleas transmit bubonic plague
• Dogs, foxes + bats transmit rabies

•Water is a vector for diseases e.g. diarrhoeal diseases

Question 12

Give an example of what disease can be transferred from what animal to a human.

Answer 12

Brucellosis, sheep → human

Question 13

What basic precautions can be taken to reduce infection rates of diseases between animals and humans?

Answer 13

• Minimise close contact with infected animals

* Wash hands thoroughly after contact with infected animals

Question 14

Can people sometimes act as vectors for animal diseases? Explain why and give an example.

Answer 14

Yes - e.g. foot-and-mouth disease

Question 15

What 7 factors increase the probability of catching a disease?

Answer 15

• Overcrowded living + working conditions
• Poor nutrition
• A compromised immune system, including people with HIV / needing immunosuppressants after transplant
• Poor waste disposal - waste provides breeding site for vectors
• Climate change
• Culture and infrastructure
• Socioeconomic factors

Question 16

How does climate change increase the likelihood of catching a disease?

Answer 16

Climate change can introduce new vectors and diseases.

E.g. increased temperatures promote spread of malaria as mosquitoes can survive over a wider area

Question 17

How does culture and infrastructure increase the probability of catching a disease?

Answer 17

Traditional medicine practises in many countries increase transmission

Question 18

How do socioeconomic factors increase the probability of catching a disease?

Answer 18

E.g. lack of trained health workers + insufficient public warning during outbreaks affects transmission rates

Question 19

How are diseases spread in plants through ‘Direct Transmission’?

Answer 19

Direct contact of a healthy plant with a diseased plant.

E.g. ring rot, tobacco mosaic virus, tomato + potato blight and black sigatoka

Question 20

Explain how diseases are spread in plants due to contaminated soil.

Answer 20

Infected plants leave pathogens or reproductive spores from protoctista / fungi in the soil. This can infect the next generation of plants.
E.G. Black sigatoka spores, ring rot bacteria, spores of TMV.

Question 21

How can pathogens spread in plants through compost?

Answer 21

Some pathogens (often spores) can survive the composting process.
When contaminated compost is used, the infection cycle is completed.

Question 22

What are the 4 vectors which transmit diseases in plants?

Answer 22

1. Water
2. Wind
3. Animals
4. Humans

Question 23

How does ‘Water’ act as a vector in spreading plant diseases?

Answer 23

Pores swim in water’s surface on leaves - raindrop splashes spread pathogens, spores etc.
E.g. spores of potato blight can swim through water onto leaves

Question 24

How does ‘Wind’ act as a vector in spreading plant diseases?

Answer 24

Bacteria, viruses and fungal spores are carried in wind.
E.g. black sigatoka blown between Caribbean islands
Blight spores can be carried in wind to other potatoes/tomatoes

Question 25

How do ‘Animals’ act as vectors in transmitting plant diseases?

Answer 25

Insects and birds carry pathogens and spores from one plant → another as they feed.
Aphids inoculate pathogens directly into plant tissue.

Question 26

How do ‘Humans’ act as vectors in spreading plant diseases?

Answer 26

Pathogens + spores are transmitted by hand, clothing, fomites, farming practices and transporting plants around the world.
E.g. TMV survives for years in tobacco products
Ring rot survives on plant machinery, potato sacks etc

Question 27

What are the 5 factors affecting the spread of diseases in plants?

Answer 27

• Planting crop varieties that are susceptible to disease
• Over-crowded plants increase likelihood of contact
• Poor mineral nutrition reduces resistance of plants
• Damp + warm conditions increase survival + spread of pathogens and spores
• Climate change

Question 28

How does climate change increase the spread of diseases in plants?

Answer 28

• Increased rainfall + wind encourage spread.
• Changing conditions allow animal vectors to spread to new areas
• Drier conditions reduce spread of disease