**Core Concept**
The relationship between prevalence and incidence of a disease is crucial in understanding the nature of the disease. Prevalence refers to the total number of cases of a disease present in a population at a particular time, while incidence refers to the number of new cases that occur within the same population over a specified period.

**Why the Correct Answer is Right**
The correct answer is related to the concept that when the prevalence of a disease is very low compared to its incidence, it implies that the disease is either fatal or easily curable. This is because the low prevalence indicates that the disease does not persist for a long time in the population, either because it is rapidly fatal or because it is quickly cured. In both cases, the number of existing cases (prevalence) remains low compared to the number of new cases (incidence). For instance, diseases like rabies or plague have a high case-fatality ratio, resulting in low prevalence despite a high incidence. Similarly, diseases like common cold or acute diarrhea have a high recovery rate, resulting in low prevalence despite a high incidence.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incorrect because a nonfatal disease can still have high prevalence if it is chronic and persists for a long time in the population.

**Option C:** This option is incorrect because the calculation of prevalence and incidence is not directly related to the nature of the disease.

**Option D:** This option is incorrect because prevalence and incidence are related and can provide valuable information about the disease.

**Clinical Pearl / High-Yield Fact**
A memorable point to keep in mind is that a low prevalence-to-incidence ratio indicates that the disease is either rapidly fatal or easily curable, and this can be a valuable clue in understanding the nature of the disease.

**Correct Answer:**
✓ Correct Answer: A. Disease is very fatal and/or easily curable