The burden of a disease in a population at a given time is best measured by:

Correct option is B

Prevalence = total number of cases (new + old) at a given time → best reflects overall disease burden.
Explanation of options: (a) ✘ Incidence = new cases only, shows risk, not total burden. (b) ✔ Correct; prevalence includes all cases, measuring disease load. (c) ✘ Mortality shows death rate, not disease burden. (d) ✘ Case fatality shows severity, not prevalence.