In the majority of cases, leptospirosis causes a mild illness but, in some people, a more severe form of leptospirosis occurs. This more severe form is commonly referred to as Weil's disease, so called after Dr Adolf Weil who first described it.n most cases, leptospirosis causes a mild illness. But, in some people, a more severe illness occurs. This more severe form is commonly referred to as Weil's disease. The main treatment for leptospirosis is antibiotics and most people make a full recovery.