In more severe cases (Weil's disease), the outlook depends on which organs of the body are involved and to what extent. A few people each year in England and Wales die from leptospirosis. Death is usually due to internal bleeding, kidney or lung complications.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.