Contributing Factors Infectious disease results from a competition for supremacy between the parasite and the host. If the parasite overcomes the host, there is a change in the general state of good health and disease develops. Several contributing factors are involved in the establishment of infectious disease. These factors determine whether the infecting organism will survive in the body. Portals of entry. In order for a pathogen to gain access to the host, the pathogen must pass through a portal of entry. One of the most common portals of entry is the mucous membranes , especially those of the respiratory, gastrointestinal, and urogenital tracts. Another important portal of entry is the skin. Penetration of the skin occurs during a wound or by a hair follicle. When microorganisms penetrate below the skin, the portal of entry is said to be the
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