What is the wisdom behind the prohibition of raising dogs inside homes in Islam, and the obligation of performing ghusl (ritual bathing) upon touching a dog's saliva?

The purification of a vessel licked by a dog is seven times, the first of which is with earth, because dogs transmit dangerous diseases such as "hydatid disease" and "rabies." Modern science has proven the ability of earth to kill germs. Therefore, Islamic law has prohibited keeping dogs except for a need, such as for farming or livestock.