The agent, the host and the environment are referred to as the “epidemiological triad” the “triad of epidemiology”. This triad is the basis of multiple causation of diseases and parasitic infestation. In other words, we need to consider the agents [pathogens and parasites] , hosts [human and livestock] and environment. The agents need a suitable environment in which to grow, multiply, spread and infect another host. And in my case an insanitary hutch above which provided suitable environment for sarcoptic mange parasite to thrive.
If proper preventive mechanism are implemented agents cannot spread and infect others, they die out. There is, therefore, a balance between agent, host and environment.