Friday, November 1, 2013

Intrinsic & extrinsic incubation period

What is incubation period?
The time interval between invasion by an infectious agent and the appearance of the first sign or symptom of the disease in question. (It is also known as intrinsic incubation period if spoken in reference to a vector borne disease.)

What is extrinsic incubation period?
In reference to vector borne diseases, it is the period of time necessary for the development of disease agent in the arthropod host or invertebrate which transmits infection.

For example: Malaria.
The extrinsic incubation period is the period of time required for the development of the parasite from the gametocyte to sporozoite stage in the body of the mosquito.
It is about 10-28 days depending on the vector species, temperature & humidity.

Alternate definition:
"The extrinsic incubation period is the time taken by the organism to complete it's development in the intermediate host."
Honestly, this definition will confuses me.
The intermediate host is the one in which the asexual cycle of the agent occurs. The intermediate host of malarial parasite is man.

If you know the explanation to the alternate definition that confuses me, do let me know! @_@
For now, I stick to the previous one =)
Hope this blog helps clear things out!

-IkaN

2 comments:

  1. In human,after the injection of plasmodium by mosquito starts the intrinsic incubation period till the first symptom of malaria occurs. So, the alternate definition is wrong.extrinsic incubation period is the time taken by the organism in definitive host,which is mosquito for plasmodium

    ReplyDelete
    Replies
    1. Yes, but this is what Wikipedia says:

      The intrinsic incubation period is the time taken by an organism to complete its development in the definitive host.
      The extrinsic incubation period is the time taken by an organism to complete its development in the intermediate host.

      Delete

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