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INFECTIOUS DISEASE. Infectious Disease Process. NATURE OF INFECTIOUS DISEASES. Pathogens: microorganisms that are capable of causing disease Infection: results when a pathogen invades and begins growing within the host - PowerPoint PPT Presentation
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INFECTIOUS DISEASEInfectious Disease Process
NATURE OF INFECTIOUS DISEASES
Pathogens: microorganisms that are capable of causing disease
Infection: results when a pathogen invades and begins growing within the host
Disease: results only if and when tissue function is impaired (i.e. burns, skin lesions)
Continued…
The body has defense mechanisms to prevent infection
In order to cause disease, pathogens must be able to enter, adhere, invade, colonize, and inflict damage
Entrance to the host: mouth, eyes, genital openings, wounds
Growth of pathogens or the production of toxins/enzymes cause disease
Some normal flora prevent diseases
MICROBES THAT CAUSE INFECTIOUS DISEASES Bacteria: Salmonella typhi, Staphylococcus aureus
Morphology: bacillus, coccus, spirillum Aerobes vs anaerobes Gram-negative (salmonella) vs gram-positive
(staphylococcus) Viruses: apart from the host cell, have no
metabolism and cannot reproduce Retroviruses: HIV and certain types of cancer Herpes viruses: chicken pox, cold sores, smallpox Rhinoviruses: common colds – mutation (rapid) leads to
no vaccine available Myxoviruses & paramysoviruses: influenza, measles,
mumps Rotaviruses: gastroenteritis
Continued…
Fungi: form spores Examples include ringworm and histoplasmosis Yeasts of Candida genus are opportunistic Antibiotics reduces normal flora, allowing yeast to
growProtoza: acquired through contaminated
food or water, or bite of an arthropod (mosquito) Diarrheal disease in the US – Giardia lamblia and
Cryptosporidium parvum Malaria – Plasmodium (in tropical environment)
…
Helminths: simple invertebrate animals, some infectious parasites Symptoms: abd. pain and diarrhea Swimmer’s itch in US – flatworm, Schistosoma Trichinella spiralis – roundworm which is ingested in
undercooked pork from infected pigs (Cause of death = respiratory paralysis)
Prions-Creuzfeldt-Jakob disease A rare, degenerative, invariably fatal brain disorder; believe
caused by an unusual "slow virus" or another organism Typically, onset of symptoms occurs about age 60, and about
90 percent of individuals die within 1 year. characterized by rapidly progressive dementia and they
eventually lose the ability to move and speak and enter a coma
Malaria
Giardia and Cryptosporidium
Helminths Worm
Prions-Creuzfeldt-Jakob disease
OCCURANCE OF INFECTIOUS DISEASES Epidemiology: study of the occurence of disease in
populations Disease reservoirs: where the infectious agent survives
(human, rodents) Example: yersinia pestis
Modes of transmission Direct contact: occurs when a person is infected by contact with
reservoir, inhaling infectious droplets – examples are AIDS, rabies, malaria, influenza, ringworm, trichninosis
Indirect contact: the pathogen is transmitted from contaminated substances such as food, soil, water (Hepatitis A), clothing, equipment (example – tetanus)
Horizontal vs vertical transmission Horizontal: transmission between individuals specifically who are not
related as a parent is to its offspring Vertical: occurs from parent to offspring, e.g., in utero, during
passage down the birth canal, or in breast milk
HOST DEFENSES AGAINST INFECTIOUS DISEASES Nonspecific mechanisms are the body’s primary defense
against disease - anatomical barriers, physiological deterrents and presence of normal flora (skin, low pH and high salinity) Anatomical barriers: nasal opening, skull, vertebral column, skin Physiological deterrents: tears, vaginal secretions, saliva, blood,
sweat, and some tissue fluids Normal flora: successfully compete with pathogens
Specific mechanisms: immunity Cell-mediated: uses T-cells; helper cells and killer cells; activate B
cells Antibody-mediated: uses B-cells Both are lympatic cells
Vaccination: produces immunity