The incidence rate of a disease is 5 times greater in women than in men, but the prevalence rates show no sex difference. The best explanation is that:
Prevalence depends upon 2 factors, the incidence and duration of illness. Given the assumption that the population is stable, and  incidence and duration are unchanging, the relationship between incidence and prevalence can be expressed as: 
Prevalence = Incidence x  Mean duration 
Note:
In the given question, if incidence for a disease is 5 times higher among females, but prevalence rate shows no sex difference, since P = I × d, thus, d (duration of disease) must be lower among females.

Either the disease is more fatal among females or
Disease is easily curable among females.