animals in the wild do not necessarily live an ideal existence: they are subject to the harsh realities of survival and where their own bodies are subject to a lowered immune-response, brought on by enervation and toxemia from a polluted World, and are therefore susceptible to viruses and other disease-causes.
"Smallpox is about as contagious as stumbling over a rock. Dr. Herbert M. Shelton slept in the same bed with his brother while the latter was in the so-called infectious stage with vesicles all over. Yet Dr. Shelton did not develop smallpox"..........Dr. Vivian Virginia Vetrano: long time Hygienist who worked with Dr Shelton.
My mentor lived (as I do) an ideal lifestyle, and was not subject to disease.
In the last 30 odd years I have been free from any disease whether classified as contagious or otherwise (except for a short period in my life when I abandoned my principles and suffered the consequences).
If you live as Nature intended, via the principles of Natural Hygiene, and conform to physiological laws, then you or anyone else will be free from the threat of both chronic and acute diseases.