ID Notes 9/12/14 An Infectious Disease ¦ Is a disease that is caused by the Invasion of a host by agents whose activities harm the host's tissues (That is, they cause disease) and can be transmitted to other individuals (that is, they are infectious). Pathogens: Microorganisms that are capable of causing disease. Most microorganisms do not cause disease. Many probably provide some protection against harmful microorganisms because thyme effectively compete with the harmful organisms. Worst case scenario, both contagious and virulent. In order to cause disease, pathogens must be able to enter the host body. They must adhere to specific host cells, invade and colonize host tissues, and inflict damage on those tissues. Some do damage at their point of entry, others travel to other parts of the host. Some reside and grow in body fluids like blood or lymph, between cells of the body tissues or inside cells. Microbes that Cause Infectious Diseases: There are 4 major types of infectious agents: : Bacteria : Viruses : Fungi : Parasites : Protozoa : Helminths BACTERIA: :Bacteria are unicellular prokaryotic organsims with no organized internal membranous structures. Their genomes are circular, double-stranded DNA. Bacteria come in many shapes ” :Bacillus (rod shaped) :coccus (spherical) (strep throat) :spirillum (helical rods) Bacteria cause disease in a variety of ways: :Bacteria can damage cells and disrupt tissue function as they grow :Many bacteria produce toxins VIRUSES : Microbiologist have found viruses that infect all organisms, from plants and animals to fungi and bacteria. Viruses, however, are not true organsims themselves. -they have no metabolism and cannot reproduce Viral structure varies Adenovirus- causes cold Influenza virus- cause flu Viruses cause disease by disrupting normal cell function.. -They do this in a variety of ways -Unlike most bacteria (not all), viruses act inside cells) Bacteria is treat