Drinking directly from cans — which can be a storehouse of germs and infections — can lead to a lot of health troubles. This is because the cans are rarely washed before being served to you to drink directly from them.
During storage they may have rats running over them, covering some of them in urine or faeces. Ingesting this by mistake can cause leptospirosis.
According to the Centers for Disease Control and Prevention, leptospirosis — which is caused by bacteria of the genus Leptospira — can affect both animals and humans.