Why was there such a high death rate during the Middle Passage?

There were diseases, that killed about 10-15 percent. The slaves have to suffer from urine, vomit, mucous, and other horrific orders. The disease was dysentery, measles, scurvy, and smallpox. The most impact was from white immigrants for being largely dehydration. Many Africans died on ship either suicide, jump off board or refuse to eat.