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Chapter 14 epidemiology.cj
 

Chapter 14 epidemiology.cj

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    Chapter 14 epidemiology.cj Chapter 14 epidemiology.cj Presentation Transcript

    • Chapter 14: Principles of Disease and Epidemiology
      • Pathology = study of disease
        • Etiology = cause of disease
        • Pathogenesis = manner in which disease develops
        • Structural and functional changes brought about by the disease
        • Final effects the disease has on the body
    • Chapter 14: Principles of Disease and Epidemiology
      • Infection = invasion or colonization of the body by pathogens
      • Disease – occurs when an infection results in any change from a state of health
        • Abnormal state where the body can’t carry out its normal fxs
      • Normal flora or normal microbiota = microbes that have permanent residence without producing disease
        • Transient microbiota – present temporarily and then disappear ex. Streptococcus in lg intestine
    • Chapter 14: Principles of Disease and Epidemiology
      • Microbial antagonism or competitive exclusion = normal microbes preventing overgrowth of pathogens
        • Ex. E. coli produces bacteriocins (proteins that are lethal to closely related bacteria) in the large intestine which inhibit the growth of pathogenic Salmonella and Shigella
    • Chapter 14: Principles of Disease and Epidemiology
      • Symbiosis = relationship between normal microbiota and the host
        • Commensalism = 1 organism benefits while the other is unaffected ex. Normal microbiota
        • Mutualism = both organisms benefit
          • Ex. E. coli in the lg intestine synthesizes vitamin K, B which provides nutrients for you and your body provides nutrients for E. coli in the lg intestine
        • Parasitism = 1 organism benefits at the expense of the other ex. Giardia lamblia
    • Chapter 14: Principles of Disease and Epidemiology
      • Opportunistic pathogens - do not cause disease in their normal habitat in a healthy person
        • Cause disease if they gain entrance to an area that they don’t usually inhabit
          • E. coli in urinary tract
          • Pneumocystis jiroveci in AIDS px – fungal pathogen causes pneumonia
      • Probiotics = live bacterial cultures ingested for beneficial effects
        • Prebiotics are chemicals to promote their growth
    • Koch’s Postulates
      • Demonstrate that a specific microbe is the cause of a specific disease
        • he worked with Bacillus anthracis to prove his postulates
      • The same pathogen must be present in every case of the disease
      • 2. the pathogen must be isolated from the diseased host and grown in pure culture
    • Koch’s Postulates
      • 3. The pathogen from the pure culture must cause disease when inoculated into a healthy, susceptible laboratory animal
      • 4. The pathogen must be isolated from the inoculated animal and be the same pathogen as the original organism
    • Exceptions to Koch’s Postulates
      • A few organisms can’t be grown in laboratory media ex. Treponema – bacteria
      • Some diseases may be caused by a variety of organisms and the specific etiology is not easy to determine from the symptoms ex. Pneumonia
      • Some pathogens may infect a # of organs or tissues and cause very different diseases or sxs ex. Streptococcus pyogenes causes sore throat, scarlet fever, puerperal fever
    • Classifying infectious diseases
      • Symptoms – felt by px, subjective and can’t be seen by a dr. ex. Pain
      • Signs – objective changes that a dr. can observe and measure ex. Fever
      • Syndrome = specific group of sxs or signs accompanying a particular disease
      • Communicable diseases = spread directly or indirectly from 1 host to another ex. Typhoid fever, TB
        • If it is highly communicable esp. thru direct contact = contagious
    • Classifying infectious diseases
      • Non-communicable diseases = caused by microbes like Clostridium tetani which enters the body through a wound
      • Incidence = the # of new cases of a disease during a particular time period
        • It is an indicator of the spread of the disease
      • Prevalence = total # of cases of a disease (old and new) in a certain area and time period
    • Classifying infectious diseases
      • Sporadic diseases occur only occasionally and in an unpredictable fashion ex. Tetanus
      • Endemic diseases are present constantly at a certain level in a particular location
        • Common cold throughout US
        • Lyme disease endemic to some eastern states
    • Classifying infectious diseases
      • Epidemic a sudden increase in morbidity (illness rate) and mortality (death rate) above the usual for a disease = many people in a given area acquire a certain disease in a short period of time
      • Pandemics = worldwide epidemics
      • Acute disease – develops rapidly but lasts for a short period of time ex. Influenza
        • Primary infection = initial acute infection
        • Secondary infection – caused by opportunist after primary infection weakens body defenses
    • Classifying infectious diseases
      • Chronic disease – develops slowly, often the rx is less severe, is continuous or recurrent for long periods of time. Ex TB, leprosy, syphilis
      • Latent disease = pathogen is inactive for long periods of time and then becomes active to produce symptoms
        • Ex. shingles
    • Classifying infectious diseases
      • Herd immunity = when most of the population is immune through vaccination or acquired immunity, few susceptible people so its hard for pathogen to find
      • Local infections – limited to small area of body ex. Boils
      • Systemic or generalized infection – microbes or their products spread throughout the blood or lymphatic system
        • Bacteremia – bacteria in the blood, toxemia – toxins, viremia - viruses
    • Classifying infectious diseases
      • Focal infection = local infection enters blood or lymph and spreads to other parts of body ex. Sinuses, tonsils
      • Sepsis = a toxic, inflammatory condition from spread of bacteria or their toxins from a local infection
        • Septicemia = sepsis from bacterial pathogens in the bloodstream
    • Classifying infectious diseases
      • Sepsis = a toxic, inflammatory condition from spread of bacteria or their toxins from a local infection
        • Septicemia = sepsis from bacterial pathogens in bloodstream
      • Sub-clinical infection – does not cause any noticeable illness
      • Predisposing factors – makes the body more susceptible to a disease
        • Gender, genetics, weather, age etc.
    • Development of disease – follows a certain sequence of events
      • Incubation period – the time between infection and signs and symptoms
      • Prodromal period – mild sxs of the disease
      • Ex. General aches, malaise
      • 3. Period of illness
        • a) Disease is most severe
        • b) Overt signs and sxs
        • c) # of WBCs may increase or decrease
        • d) If body doesn’t overcome the pathogen the px. May die
    • Development of disease
      • 4. Period of decline
        • a) Signs and sxs subside
        • b) Px susceptible to secondary infection
      • 5. Period of convalescence
        • a) Px regains pre-diseased state
        • b) Px can serve as a reservoir of disease and spread infection to others
            • Ex. Typhoid fever, cholera
    • Reservoirs of Infection
      • Reservoirs are sites that are a continual source of the pathogen from which they may be transmitted
      • All pathogens must have 1 or more reservoirs to exist
    • Reservoirs of Infection
      • Human reservoirs
      • a) people harbor and transmit pathogens to others directly or indirectly
      • b) these people may be active carriers and are diseased and obvious transmitters or are healthy carriers and have no sxs
      • c) people are the only known reservoirs for smallpox, gonorrhea, measles, polio, etc.
      • d) smallpox was eradicated once the last known infected person was cured
    • Reservoirs of Infection
      • The reservoir may be different from the source of the pathogen
        • Typhoid Mary was a reservoir of typhoid fever and shed typhoid bacilli in her feces
        • The immediate source would be water or food contaminated with the fecal material – she was a cook early 1900s
    • Reservoirs of Infection
      • Animal reservoirs
        • Diseases that occur in wild and domestic animals that can be transmitted to humans are called zoonoses
        • Transmission is direct contact with infected animals or their hides, fur or feathers, contamination of food or water, insect vectors, or eating infected animal products
    • Reservoirs of Infection
      • Nonliving reservoirs
        • Some organisms are able to survive and multiply in nonliving environments such as soil and water
        • Clostridium that causes tetanus and botulism can survive many years in the soil
        • Hookworms (a helminth) deposit their eggs into the soil
        • Water contaminated by human or animal feces cause GI tract disease (list includes bacteria, viruses, protozoa)
    • Transmission of disease
      • Transmission is the mechanism by which an infectious agent is spread to a susceptible person
      • Contact transmission
        • Direct – person to person by kissing, touching, bites, or sexual intercourse
          • Colds, flu, STD’s
        • Droplet infection – pathogen spreads in saliva or mucus droplets by coughing or sneezing, travel short distance from reservoir
    • Transmission of disease
      • Contact transmission cont.
        • Indirect – involves a nonliving objects = fomite ex. Cup, towel
      • Vehicle transmission
        • Inanimate reservoirs – food, water, blood
        • Airborne transmission – pathogens traveling in droplets or on dust for distances over 1 meter
          • Viruses, bacteria, fungal spores
    • Transmission of disease
      • Vectors = animals that carry pathogens from 1 host to another, arthropods most important
      • Mechanical transmission – carry pathogens passively on their bodies and feet to food
      • Biological transmission – arthropod passes pathogen in a bite or feces which enter wound caused by the bite
    • Nosocomial infections
      • Nosocomial infections are those infections acquired by pxs or hospital staff in a hospital or long term health care facility and account for 20,000 deaths/year in US
      • 3 conditions that compromise a host
        • Broken skin or mucous membranes
        • Suppressed immune system
        • Impaired defense cell activity – drugs, radiation, steroids, etc.
      • Pathogens transmitted by surgical procedures, fomites, medical equipment, air, H2O, people
    • Emerging Infectious Diseases
      • Emerging infectious diseases show an increase in incidence or a potential for increase in the near future ex. West nile virus, SARS, whooping cough
      • Factors that contribute to emerging disease
        • New strains from genetic recombination
        • New serovars ex. Vibrio cholerae O139
        • Use of Abs and pesticides encourage growth
        • Global warming and weather changes may increase the distribution and survival of reservoirs and vectors
        • Diseases may spread to new geographic areas
    • Epidemiology
      • Epidemiology = scientific study of the source and transmission of a disease with in a population
      • Epidemiology has a long hx
        • Hippocrates 460 -377 BC made observations about the link between malaria and yellow fever and swamps (breeding ground for the mosquito vector)
        • Edward Jenner – late 1700’s – observations of cowpox led to his vaccination for smallpox
    • Epidemiology
      • Epidemiology
        • Ignaz Semmelweis – mid 1800s proved that childbed fever resulted from physicians not washing their hands after dissections
        • British epidemiologist John Snow investigated cholera outbreak in London
          • Most of the cholera victims lived in the Broad Street area and used the water from the Broad Street Pump
          • Removing the pump handle ended the cholera epidemic
    • Epidemiology
      • Descriptive epidemiology – collecting all data that describes the occurrence of the disease
        • Info of affected individuals – place, time, age, M/F
        • Snow’s approach was descriptive
        • The approach is looking backwards
    • Epidemiology
      • Analytical epidemiology – look for a common factor among the affected persons that might have preceded the disease
      • Experimental epidemiology tests a hypothesis ex. Effectiveness of a drug
        • 2 groups – 1 to receive the drug and 1 a placebo
        • Compare groups to determine if any difference with drug
    • Center for Disease Control and Prevention (CDC)
      • Branch of US Public Health Service in Atlanta, Georgia – which is the central source of information in the US
      • CDC issues the Morbidity and Mortality Weekly Report (MMWR) at www.cdc.gov
      • Notifiable diseases – drs and health care workers must report to Public Health Service ex. AIDS, measles, gonorrhea, tetanus, typhoid fever