Question

The German physician Robert Koch (1843-1910) established a procedure for diagnosing causes of infection. In his research with anthrax, Koch developed the following four-step procedure, known as Koch’s postulates, as a guide for identifying specific pathogens. Biologists have used Koch’s postulates to identify many pathogens

1. The pathogen must be found in an animal with the disease and not in a healthy animal.
2. The pathogen must be isolated from the sick animal and grown in a laboratory culture.
3. When the isolated pathogen is injected into a healthy animal, the animal must develop the disease.
4. The pathogen should be taken from the second animal and grown in laboratory culture. The pathogen should be the same as the original pathogen.

Looking at the above statements, how is it possible that, in spite of being injected with a pathogen isolated from a sick animal, another animal remains healthy?

A) There is not enough information to make a conclusion

B) The healthy animal immune system recognizes the pathogen as self

C) Such incident cannot happen – the injected animal will always be sick

D) Most likely, the other animal already encountered the e specific pathogen and the animal is immune

Answer 1

A)There is not enough information to make a conclusion.

• The animals must be of same species and grown in same conditions.
• When the pathogen enters the body the blood and lymph detect the specific pathogen associated molecular patterns(PAMPs) on the pathogen surface. These PAMPs allows the immune system to distinguish between the 'self' and 'other' so that it doesn't attack the host.Thus the pathogen cannot be identified as self.
• Such incidents may happen if the an individual animal or a species is immune to that pathogen due to genetic factors. The antibodies may also pass from the parent to the fetus via placenta causing immunity against a particular pathogen.
• There is chance that the animal has encountered the pathogen before and is now immune due to antibodies in its blood , but animals grown in laboratory are under surveillance and doesn't interact or interfere with the natural environment.So their chances of getting infected are low unless injected for studies.But it is not mentioned in the above statetements about the animal that is selected.
• If it is a laboratory animal and grown under lab conditions and if the pathogen affects others of its kind and cause sick condition then the chosen animal will also be sick.