**Core Concept**
The concept being tested is the measurement of the intensity of a parasitic infection, specifically filariasis, in a population. This is a crucial aspect of epidemiology, which helps in understanding the disease burden and planning effective control measures.

**Why the Correct Answer is Right**
The percentage of people examined showing microfilaria in blood and/or disease manifestation is known as the intensity of infection. This measurement is essential in assessing the burden of disease in a community. In the context of filariasis, microfilariae are the larval stage of the parasite that circulates in the blood, causing disease manifestations such as lymphedema, elephantiasis, and acute inflammatory episodes.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the measurement of disease intensity.
**Option B:** This option is incorrect because it refers to the prevalence of disease, which is the proportion of people in a population who have a particular disease at a given time, not the intensity of infection.
**Option C:** This option is incorrect because it refers to the incidence of disease, which is the number of new cases of a disease that occur in a population over a specified period, not the intensity of infection.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the intensity of infection is a critical factor in determining the effectiveness of control measures for filariasis. Intensive transmission control measures, such as mass drug administration, are often more effective in areas with high intensity of infection.

**Correct Answer: B. Prevalence.**