The fever can last for around five days followed by a marked deterioration. Most people will recover completely with treatment, but there are cases where the illness causes serious damage to internal organs and can lead to death. Weil's disease (an acute form of infection) is commonly treated by antibiotics.he fever can last for around five days followed by a marked deterioration. Most people will recover completely with treatment, but there are cases where the illness causes serious damage to internal organs and can lead to death. Weil's disease (an acute form of infection) is commonly treated by antibiotics.