BACTE: INFECTION

• SAPROPHYTES: from Greek sapros - decayed; and phyton - plant
• SAPROPHYTES are free-living microbes that live on dead or decaying organic matter.
• Parasites are microbes that can establish themselves and multiply in the hosts.
• Pathogens: from Greek pathos, disease; and gen, to produce
• Pathogens are the microorganisms or agents, which are capable of producing disease in the host.
• Pathogens: Its ability to cause disease is called pathogenicity.
• Primary (frank) pathogens are the organisms, which are capable of producing disease in previously healthy individuals with intact immunological defenses.
• Opportunist pathogens rarely cause disease in individuals with intact immunological and anatomical defenses.
• Opportunist pathogens are able to cause disease only when such defenses are impaired or compromised.
• Commensals (organisms of normal flora) are the microorganisms that live in complete harmony with the host without causing any damage to it.
• Infection - the lodgment and multiplication of a parasite in on the tissues of a host constitute infection.
• Primary infection: Initial infection with a  parasite in a host
• Reinfections: Subsequent infections by the same  parasite in the host
• Secondary infection: When a new parasite sets up an infection in a host whose resistance is lowered by a preexisting infectious disease,
• Local infection: (more appropriately local sepsis) indicate a condition where, due to infection or s epsis at localized sites such as appendix or tonsils, generalized effects are produced 
• Cross infection: When a patient already suffering from a disease, a new infection is set up from another host or another external source, it is termed cross-infection.
• Cross-infections occurring in hospitals are called nosocomial infections (from Greek nosocomion hospital).
• Iatrogenic infection: infection refers to physician induced infections resulting from investigative, therapeutic or other procedures.
• Inapparent infection: is one where clinical effects are not apparent.
• Subclinical infection: is often used as a synonym to inapparent infection.
• Atypical infection: is one in which the typical or characteristic clinical manifestations of the particular infectious disease are not present.
• Latent infection: Some parasites, following infection, may remain in the tissues in a latent or hidden form proliferating and producing clinical disease when the host resistance is lowered. This is termed latent infection.
• Human Beings - most common source of infection for human beings is human beings themselves. The parasite may originate from a patient or carrier.
• Human beings - a carrier is person who harbors the microorganisms without suffering from any ill effect` because of it.
• Convalescent carrier: who has recovered from the infectious disease but continues to harbor large numbers of pathogen.
• Healthy carrier is an individual who harbors the pathogen but is not ill.
• Incubatory carrier: is an individual who is incubating the pathogen in large numbers but is not yet ill.
• Temporary carriers: Convalescent, healthy, and incubatory carriers may harbor the pathogen for only a brief period (hours, days, or weeks) and lasts less than six months.
• Chronic carriers: harbor the pathogen for long periods (months, years, or life).
• Contact carriers:  is applied to a person who acquires the pathogen from a patient.
• Paradoxical carrier: a carrier who acquires the pathogens from another carrier.
• Many pathogens are capable of causing infections in both human beings and animals. Therefore, animals may act as a source of infection of such organisms. These, animals serve to maintain the parasite in nature and act as reservoir and they are, therefore, called reservoir hosts.
• Zoonosis: The diseases and infections, which are transmissible to man from animals
• Insects that transmit infections are called vectors.
• Blood-sucking insects, such as mosquitos, ticks,mites, flies, and lice may transmit pathogens to human beings and diseases so caused are called arthropod borne diseases
• Vector-borne transmission can be of two types either mechanical (external) or biological (internal).
• Mechanical vector: The disease agent is transmitted mechanically by the arthropod. Examples: Transmission of diarrhea, dysentery, typhoid, food poisoning and trachoma by the house fly.
• Biological vectors: those in whom the pathogens multiply sufficiently or has undergone a developmental cycle. The interval between the time of entry of the pathogen into the vector and the vector becoming infective is called the extrinsic incubation period. Examples: Aedes aegypti mosquito in yellow fever, Anopheles mosquito in malaria.
• Water may act as the source of infection either due to contamination with pathogenic microorganisms.
• Contaminated food may act as source of infection of organisms causing food poisoning, gastroenteritits, diarrhea and dysentery.