If you visit remote places in under-developed countries, you will find many flies. The flies are a nuisance (or even torture) to the animals and to human. Worse still, the flies will spread diseases, making people ill.
Why are there so many flies ? Because of animal/human wastes. They provide food to the flies as well as a place for them to lay eggs.
(My opinion is that even for National Parks, we, human, should build septic tanks and TEACH the animals to drop their waste there. LORD gave the management of the world onto us, human, and we should do our duty [Gen 1:28].)
Many elderly people in elderly homes suffer from fleas. Why are there so many fleas, because dead skin from old people provide food for them. If the workers do not bathe the people often, do not change blankets often, do not vacuum the rooms frequent enough, such skin/tissues will provide food for the fleas and they flourish.
People living in modern cities will not have to consider these. Clean water comes from the tap, waste water goes down the drain to water treatment plant, refuse are collected to be incinerated or buried. They have vacuum cleaners in the house, and cleaning water is plentiful.
Not so in under-developed places. If people are not careful with their waste, they provide food for the fleas, flies, insects, rats, .... Lots and lots of people become sick with diseases unheard of among us. Some insects will even lay eggs in human - a terrible sight.
People in modern cities face uncleannesses not visible to them. They eat lobsters, oysters, pigs, shell fish, lot of animal fat, ... those food LORD taught us to avoid [Lev 11], and then suffer from heart disease, liver failure, kidney failure, cancer, depression, chemical imbalance, .... and have to take in lot of medicine, have to undergo therapies of various sort, or even operations. These are "torture in real life", overlooked by many.
People touch unclean things, and forget to bathe, and have fever or temperature or sicknesses.
These are physical uncleannesses. But there are spiritual uncleannesses.
Say to all congregation of the people of Israel, You shall be holy; for I the LORD your GOD am holy. [Lev 19:1]
Blesses are the pure in heart, for they shall see God. [Mt 5:7]
If we are not pure and clean, LORD will not see us.
Physical uncleanness will cause sickness, so is spiritual uncleanness.
For a heart full of envy, jealousy, evil-will, lust after fleshy passions, lust after money, ... the body will pay the price of it.
Let every one of us pay special attention to cleanliness : both physical and spiritual, and avoid unnecessary illnesses.
The Following are some teachings of LORD about physical cleanliness :
(Note : [Lev 5:2] teaches us not to touch carcass of unclean beast, or carcass of unclean cattle, or carcass of unclean swarming things. In times past, people must avoid touching such, if they touch such, they will be fined a pigeon (or turtle dove), or a sheep, as guilt/sin offering).
Flesh that touches any unclean things shall not be eaten; it shall be burned with fire. [Lev 7:19]
It shall be a perpetual statute throughout your generations, in all your dwelling places, that you eat neither fat nor blood. [Lev 3:17]
You shall not eat the blood of any creature, for the life of every creature is its blood; whoever eats it shall be cut off. [Lev 17:14]
And every person that eats what dies of itself or what is torn by beasts, whether he is a native or a sojourner, shall wash his clothes, and bathe himself in water, and be unclean until the evening, then he shall be clean. [Lev 17:15]
Say to the people of Israel, These are the living things which you may eat among all the beasts that are on the earth. Whatever parts the hoof and is cloven-footed and chew the cud, among the animals, you may eat. Nevertheless among those that chew the cud or part the hoof, you shall not eat these: The camel, because it chews the cud but does not part the hoof, is unclean to you. And the rock badger, because it chews the cud but does not part the hoof, is unclean to you. And the hare, because it chews the cud but does not part the hoof, is unclean to you. And the swine, because it parts the hoof and is cloven-footed but does not chew the cud, is unclean to you. Of their flesh you shall not eat, and their carcasses you shall not touch; they are unclean to you.
He who touches the dead body of any person shall be unclean seven days; he shall cleanse himself with the water (water of impurity) on the third and on the seventh day, .... [Num 19:11]
This is the law when a man dies in a tent: every one who comes into the tent, and every one who is in the tent, shall be unclean seven days. And every open vessel, which has no cover fastened upon it, is unclean. Whoever in the open field touches one who is slain with a sword, or a dead body, or a bone of a man, or a grave, shall be unclean seven days. For the unclean they shall take some ashes of the burnt sin offering, and running water shall be added in a vessel; then a clean person shall take hyssop, and dip it in the water, and sprinkle it upon the tent, and upon all the furnishings, and upon the persons who were there, and upon him who touched the bone, or the slain, or the dead, or the grave; and the clean person shall sprinkle upon the unclean on the third day and on the seventh day; thus on the seventh day he shall cleanse him, and he shall wash his clothes and bathe himself in water, and at evening he shall be clean. [Num 19]