Inflammation. Inflammation in the muscle is the cause of the pain.
Flu-like symptoms. The disease starts with a fever, headache, and other flu-like symptoms. After recovering from those symptoms, you can then go on to develop meningitis, kidney failure, and liver damage with jaundice.
Calf pain/leptosporo. It is presumed to be due to combination of factors 1generalised effect of fever and constitutional symptoms causing pain in muscles of calf and also arms 2lepto causing local inflammatory responce directly in calf muscle.