The dissemination of plant parasites is favored by many circumstances not always obvious, whence an air of mystery regarding epidemics was easily created in earlier times.
Endemic diseases are unknown and epidemics are rare.
The origin of these two epidemics was obscure.
The Malays formerly suffered severely from smallpox epidemics, but in the portion of the peninsula under British rule vaccination has been introduced, and the ravages of the disease no longer assume serious dimensions.
The epidemic nature of wheat-rust was known to Aristotle about 350 B.C., and the Greeks and Romans knew these epidemics well, their philosophers having shrewd speculations as to causes, while the people held characteristic superstitions regarding them, which found vent in the dedication of special festivals and deities to the pests.