Causes of infectious disease

Question 1

Louis Pasteur overview

Answer 1

• People in 1800s believed diseases would spontaneously generate
• Pasteur showed that air carried microbes which caused contamination

Question 2

Pasteur experiment

Answer 2

1. One broth in a swan neck flask and another in a non swan neck flask. Both broths are boiled to kill any existing microbes
2. Flasks are left to sit
3. Swan neck: broth remained clear with no signs of microbial growth
   Non swan neck: broth becomes cloudy overtime due to microbial growth

The experiment helped people realise that microbes do not spontaneously generate in sick people but are carried by air

Question 3

Koch’s postulates overview

Answer 3

• Identified that a specific type of bacteria caused a specific disease
• Cannot be used on prions and viruses as they have complex lifestyles that may not reinfect after being cultured

Question 4

What are the four Koch’s postulates?

Answer 4

1. The suspected causative agent must be absent from all healthy organisms but present in all diseased organisms
2. The causative agent must be isolated from a diseased organism and grown in pure culture
3. The cultured agent must cause the same disease when inoculated into a healthy, susceptible organism
4. The same causative agent must be re-isolated from the inoculated, diseased organism

Question 5

What factors may contribute to the development of infectious disease?

Answer 5

1. Host factors: poor nutrition
2. Pathogen factors: transmission ability
3. Environmental factors: favourable environment

Question 6

What are the social/economic impacts of I.D. on agricultural production?

Answer 6

1. Decrease in body weight of livestock reduces fertility –> increases the need for feeding –> extra cost
2. Lower livestock product production
3. Fewer marketing opportunities
4. Stress to the producer