Infection, Type of Infection & Disease Important Term & Definition A. Infectious agent : a microorganism which is capable of producing an infection. (bacteria, virus, fungi, parasite and prion) B. Infection: Invasion of the body tissue of a host by an infectious agent whether or not it causes disease v Pathogenicity : refer to the ability of microbial species to produce disease v Virulence is the ability of strain of microorganisms to cause disease. M. Tuberculosis contain strain of a varying degree of virulence. Eg. The vaccine contains avirulent strain. o Virulence of a strain is not constant and may undergo variation o Exaltation : enhancement of virulence of the strain of Microorganism o Attenuation: reduction of virulence of a strain v Invasiveness : the ability of an organism to spread within the host tissue after establishing infection. v T