Mites are to bees what HIV is to humans. HIV destroys a human being’s immune system, and the result is that in full-blown AIDS, the person dies of infections that can rampage due to a lack of immune system.
In bee races susceptible to one or both types of mite, the presence of mites will cause an increased incidence of disease in the bees with the result that the bees become weak, and eventually succumb to illnesses.