Infection

• Primary infection: Initial infection with organism in host.
• Reinfection: Subsequent infection by same organism in a host.
• Superinfection: Infection by same organism in a host before recovery.
• Secondary infection: When in a host whose resistance is lowered by preexisting infectious disease, a new organism may set up in infection.
• Focal infection: It is a condition where due to infection at localized sites like appendix and tonsil, general effects are produced.
• Cross infection: When a patient suffering from a disease and new infection it set up from another host or external source.
• Nosocomial infection: Cross infection occurring in hospital. Diseases acquired in hospital settings
• Saprophytes: They are free living organisms which fail to multiply on living tissue and so are not important in infectious disease
• Parasites: They are organisms that can

  establish themselves and multiply in hosts.

  They may be pathogens or commensal.
• Anthroponosis: human to animal
• Infectious diseases transmitted from animals to man are called zoonosis.
• Insects: The diseases caused by insects are called arthropod borne disease.
• Pathogenecity is referred to the ability of

  microbial species to produce disease.
• Virulence is referred to the ability of microbial strains to produce disease.
• Adhesion: The initial event in the pathogenesis of many infections is the attachment of the bacteria to body surfaces. This attachment is specific reaction between surface receptors and adhesive structures on the surface of bacteria (adhesins).
• Invasiveness is the ability of organism to spread in a host tissue after establishing infection.
• Toxigenicity. Bacteria produce two types of toxins – exotoxins & endotoxins
• Communicability is the ability of parasite to spread from one host to another.
• Coagulase is a virulence factor that causes clotting. Coagulase enabel S.aureus to clot plasma and form a sticky coat of fibrin for protection from phagocytes, antibodies and other host defense mechanisms by

  forming fibrin barrier around bacteria
• Fibrinolysin promotes the spread of infection by breaking down the fibrin barrier in tissues.
• Biofilm communities are responsible for much of the biological activity attributed to bacteria in the wide range of habitats occupied by these biochemically complex microorganisms
• These communities represent a higher order of structure and function than is found when bacteria are grown in broth culture
• Plaque is a biofilm on the surfaces of the teeth which secretes acids that destroy teeth and gums
• Biofilm bacteria can be up to 1000 times more resistant to antimicrobial stress (e.g. antibiotics and disinfectants) than free-swimming bacteria of the same species.
• Quorum Sensing: Many groups of bacteria can communicate - by releasing and detecting chemical pheromones to gauge their population density - the molecular structure of a key protein in this interbacterial communication has been solved.
• Hyaluronidase: Enables pathogens to invade deeper tissues
• Leucocidins: It destroys white blood cells
• Leucocidins damage polymorphonuclear leucocytes.
• Ig A1 proteases: split IgA and inactivates its antibody activity
• Hemolysin is produced by some organisms capable of destroying erythrocytes.
• minimum infection dose (MID)
• minimum lethal dose (MLD)
• Vibrio cholerae is effective orally. No effect when it is introduced subcutaneously
• Streptococci can initiate infection whatever be the mode of entry.
• Circulation of bacteria in the blood is known as bacteremia (viruses – virusemia).
• Septicemia is the condition where bacteria circulate and multiply in the blood, form toxic products and cause swinging type of fever
• Pyemia is a condition where pyogenic bacteria produce septicemia with multiple abscesses in the internal organs such as the spleen, liver and kidney.
• Endemic diseases are ones that are constantly present in a particular area.
• Typhoid fever is endemic in most parts of India.
• An epidemic disease is one that spreads rapidly, involving many persons in an area at the same time.