+An **infectious disease** occurs when harmful [Pathogen](/wiki/pathogen) invade a living host, disrupting its normal functions. The body's [Immunity](/wiki/immunity) then works to combat these invaders, influencing the severity and outcome of the illness. These conditions can spread, creating ripples through populations.
+## See also
+- [Virus](/wiki/virus)
+- [Bacteria](/wiki/bacteria)
+- [Vaccine](/wiki/vaccine)
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