These small organisms, too small the mathematics of infectious diseases pdf see without magnification, invade humans, animals, and other living hosts. Their growth and reproduction within their hosts can cause a disease. Even when a pathogen is the principal cause of a disease, environmental and hereditary factors often influence the severity of the disease, and whether a potential host individual becomes infected when exposed to the pathogen.

1546, and expanded upon by Marcus von Plenciz in 1762. The nature of this doctrine prevented them from understanding how diseases actually progressed, with predictable consequences. Europe, though doctors were unaware of how it worked or how to extend the principle to other diseases. Similar treatments had been prevalent in India from just before AD 1000.

By the end of the 1880s the miasma theory was struggling to compete with the germ theory of disease. Viruses were discovered in the 1890s. The miasma theory was the predominant theory of disease transmission before the germ theory took hold towards the end of the 19th century. The theory posited that diseases were the product of environmental factors such as contaminated water, foul air, and poor hygienic conditions.

Such infections, according to the theory, were not passed between individuals but would affect those within a locale that gave rise to such vapors. On the Nature of Things, ca. Galen speculated that plagues were spread by “certain seeds of plague”, which were present in the air. Galen explained that patients might relapse during recovery from a fever because some “seed of the disease” lurked in their bodies, which would cause a recurrence of the disease if the patients didn’t follow a physician’s therapeutic regimen.

The diseases were categorised based on how they were transmitted, and how long they could lie dormant. He devised an experiment in 1668 in which he used three jars. He had one of the jars open, another one tightly sealed, and the last one covered with gauze. After a few days, he observed that the meatloaf in the open jar was covered by maggots, and the jar covered with gauze had maggots on the surface of the gauze. However, the tightly sealed jar had no maggots inside or outside it. He also noticed that the maggots were found only on surfaces that were accessible by flies. From this he concluded that spontaneous generation is not a plausible theory.