Man is both intermediate and definitive host for –
**Core Concept**
The question is testing the student's understanding of the lifecycle of parasites, specifically those that require two hosts to complete their life cycle. In this context, the intermediate host is where the parasite undergoes asexual reproduction, while the definitive host is where the parasite reaches sexual maturity and reproduces sexually.
**Why the Correct Answer is Right**
In the lifecycle of certain parasites, such as Plasmodium species (causing malaria) and Schistosoma species (causing schistosomiasis), humans serve as both intermediate and definitive hosts. For example, in the case of malaria, the Plasmodium parasite undergoes asexual reproduction in the intermediate host (mosquito), while it reaches sexual maturity and reproduces sexually in the definitive host (human). This unique lifecycle is a key aspect of these parasites' biology and is crucial for understanding their transmission and control.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because humans are not typically intermediate hosts for this parasite. The intermediate host for this parasite is usually another animal species.
**Option B:** This option is incorrect because while humans may be infected with this parasite, they are not both intermediate and definitive hosts in its lifecycle. The intermediate host for this parasite is usually a different animal species.
**Option C:** This option is incorrect because humans are not typically intermediate hosts for this parasite. The intermediate host for this parasite is usually another animal species.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the lifecycle of parasites can vary greatly between different species, and understanding the specific host requirements for each parasite is crucial for developing effective control measures.
**Correct Answer: D. Schistosoma. Schistosomas are parasites that use humans as both intermediate and definitive hosts.**