Flies carry many different kinds of germs, such as typhoid, cholera, dysentery, scarlet fever, diphtheria, and even the eggs of intestinal worms and parasites.
Diphtheria is a highly contagious disease caused by certain germs occasionally found in the throat of apparently normal people! These people are knows as "carriers" of the germs.
Flies not only carry germs on their bodies. Each fly has a sort of pouch or reservoir which it fills when it eats. After taking a full meal at some filthy rubbish dump.
All too often we are out own worst enemies. Nature has been wonderful kind of us, endowing us with enormous vitality and power to overcome almost every types of illness.