Question

1. What conditions must be met before a specfic pathogen is proved to cause a disease?

2. Name five general types of pathogens.

3. What are some ways in which pathogens spread?

4. How do bacteria and viruses differ in the ways they affect cells in the body?

5. How did the work of Lister and Koch support Pasteur's germ theory of disease?

Answer 1

Answer 1: According to the scientist Robert Kotch four conditions must be met by the pathogen that causes a particular disease. These conditions are referred to as Kotch's postulates.  These conditions are as follows:

1. The same specific pathogen must be observed every time on the onset of the particular disease.
2. Isolation and pure culture (in vitro) of that specific pathogen must be possible.
3. The disease (thought to be caused by the specific pathogen) must be developed in a healthy animal if a specific pathogen from the pure culture is injected into the animal.
4. If the pathogen is again isolated and cultured from the diseased animal then it should be exactly similar to the specific pathogen in concern.

Answer 2: Bacteria, Viruses, Fungi, Protozoa, and Parasites are the names of five general types of pathogens that cause various diseases.

Answer 3: Pathogens can spread through contaminated air, water, and food, contaminated surfaces, or by insect bites. The direct transfer of pathogen can also occur by touching and coming in contact with infected body fluid.

Some examples are as follows:

• Coronavirus spreads through the air and also through the contaminated surfaces.
• Ptyphoid spreads because of contaminated food and water.
• The insect mosquito is the vector for the disease of malaria.
• Rabies virus spreads when the infected dog bites a healthy person.

Answer 4: Virus is considered to be present at the edge of living and non-living which means that it is non-living outside the cell and becomes active and living only when enters into the host cell. But bacteria can survive inside and outside of the host cell.

Viruses are more host-specific than bacteria.

Bacteria can cause disease even when they are outside the host cells by producing exotoxins. For example, Clostridium botulinum produces exotoxins that cause food poisoning.

But Viruses can cause disease only when they are entered into the host cell. They enter into the cell and use the cell's machinery for its own propagation. In this way, viruses increase their number in the host cell and ultimately released by bursting the cell.

Answer 5: After the Pasteur's germ theory the British surgeon-scientist Joseph Lister started cleaning their surgical tools by weak carbolic acid. By doing this he observed a drastic decrease in the number of patients who died due to infection after the surgical procedures.

The scientist Robert Koch injected pathogen from the diseased animal to the healthy animal. And he observed that the healthy animal also developed the same disease.

In this way, Pasteur's germ theory was supported by Joseph Lister and Robert Koch.