“Occupational disease” is limited to only those diseases which arise out of and in the course of the employee’s employment. The diseases shall have a direct causal connection with the employment and must have followed as a natural incident thereto from injurious exposure occasioned by the nature of the employment. An occupational disease must be incidental to the character of the business, occupation, or process in which the employee was employed and not independent of the employment. The disease need not have been foreseen or expected, but, after its contraction, the disease must appear to have had its origin in a risk connected with the employment and to have resulted from that source as an incident and rational consequence. A disease which follows from a hazard to which an employee has or would have been equally exposed outside of that occupation is not compensable as an occupational disease.