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Pathology & Concerns Pathology - scientific study of disease !"#$%&'()* concerns for pathology include: +,-&#-& . /$,0&1,23245 1 Etiology - the cause of disease Pathogenesis - the manner in which the disease develops, changes caused by the disease and the final effects on the body 2 Infection & Disease Normal Microorganisms Normal microbiota (flora): microorganisms which colonize the body, but do not produce disease under normal circumstances (those which are present, but only temporarily, are transient microbiota) Infection - invasion or colonization of the body by pathogenic microorganisms Normal microbiota can prevent disease or overgrowth of harmful organisms through competition - called microbial antagonism this differs from… This can be direct competition for nutrients, or through production of bacteriocins, proteins which inhibit other bacteria of similar species Disease - when an infection causes a change from the normal state of health 3 4 Microorganisms and Disease Opportunism Symbiosis - the host and microbiota living together Opportunistic pathogens are organisms which do not normally cause disease in a healthy person, but will cause disease if the person is weakened This can occur in several formats… Commensalism - one benefits and the other isn't harmed for example, from previous disease, or immunosuppression such as cancer therapy Mutualism - both benefit Parasitism - host is harmed 5 6 1 Etiology Determined via Koch's postulates 1. 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. 3. The pathogen from the pure culture must cause the disease when it is inoculated into a healthy, susceptible laboratory animal. 4. The pathogen must be isolated from the inoculated animal and must be shown to be the original organism. 7 8 Unculturable Organisms Modifications to Koch's Postulates necessary for unculturable diseases. Can use molecular methods or compare cultures from different specimens (mouse, guinea pig etc…) for intracellular parasites eg. Treponema pallidum (syphilis) Mycobacterium leprae (leprosy) 9 10 Classifying Infectious Diseases 11 Classifying Infectious Diseases Symptoms - subjective changes in body function (pain, malaise - not easily measurable) Communicable disease - disease which spreads from one host to another (ex. genital herpes) Signs - objective changes that can be observed and measured (eg. lesions, fever, etc.) Contagious disease - disease which spreads easily from person to person (ex. chickenpox) Syndrome - a group of symptoms or signs which may always accompany a particular disease. Noncommunicable disease - not spread from host to host (eg. opportunistic infections caused by normal flora, or disease such as tetanus introduced from outside the body) 12 2 Frequency of Disease Occurrence of Disease Incidence - the fraction of a population that contracts the disease during a particular time period Sporadic - occurs only occasionally Prevalence - fraction of a population having the disease at a specified time. Endemic - constantly present Epidemic - many people in a given area acquire a certain disease in a relatively short time period. Pandemic - worldwide epidemic 13 14 Severity & Duration of Disease Emerging Infectious Diseases new or changing diseases showing an increased incidence in the recent past or a potential to increase in the near future. Acute - develops rapidly, but last only a short time (flu) Zoonoses – disease of animals which can be transmitted to humans (Table 14.2, p. 419) Chronic - develops more slowly, and often is less severe, but can be continual or recurrent Latent - inactive for a time (may be long or short) 15 16 Extent of Host Involvement Classification of Infection How much of the body is affected? Local infection - limited to a relatively small portion of the body. Primary infection - an acute infection that causes the initial illness. Systemic (generalized) infection - spread throughout the body !bacteremia - bacteria present in blood !septicemia - microorganisms multiply in the blood !toxemia - presence of toxins in the blood (tetanus) !viremia - is viruses in the blood 17 Secondary infection - an opportunistic pathogen taking advantage of the weakened defenses due to the primary infection. 18 3 Spread of Infection - Reservoirs Transmission of Disease Reservoirs: source of infection, can be living or non-living. Contact transmission - direct or indirect contact, or by droplet transmission. No intermediate. Ex. kissing, touching. Humans - transmit from person to person. Called carriers, some of which may not exhibit symptoms. Indirect contact - spread to susceptible host through a non-living object, called a fomite. Animals - (zoonoses) Can occur through contact with the animal, with animal waste, ingestion of animal products, or by insect vectors. Droplet transmission - mucus droplets spread a short distance (less than one meter) by talking, sneezing, coughing, etc. Non-living - soil and water. (ex. fungi in soil, botulism and tetanus; water - cholera) Vehicle transmission - transmission of disease agents by a medium such as food, water or air (more than 1 meter) Vector transmission - animals which carry pathogens from one host to another. (arthropods commonly vectors) 19 20 Nosocomial Infections Nosocomial Infections - those infections not evident (present or incubating) at the time of admission to a hospital. (5-15% of all hospital patients acquire nosocomial infections) Factors microorganisms in the hospital weakened state of the patient (primary infection, drug or radiation therapy, burns or surgery) chain of transmission in the hospital - can transfer patient to patient, staff to patient 21 used to be mainly Gram-positive, but now mostly Gram-negatives 22 Control of Nosocomials preventative procedures Good aseptic technique isolation use of disposable or carefully sterilize equipment before reusing monitoring procedures to trace causes. 23 24 4 Development of a Disease Incubation Period Incubation period - time between infection and appearance of symptoms or signs. Death if immune response or medical intervention fail Disease Decline Illness Prodromal period - in some diseases, short period of mild symptoms. Prodromial Period Convalescence Period of Illness - most acute. Exhibits overt signs and symptoms. If not successfully overcome, the patient dies during this period. If overcome, then enter the Period of Decline - signs and symptoms diminish, susceptible to secondary infections. Period of Convalescence - regains strength and returns to prediseased state 25 26 Epidemiology CDC Epidemiology - study of when and where diseases occur and how they are transmitted in populations. Case reporting of certain disease cases to the state and national level. Used to keep track of the spread of diseases. Descriptive epidemiology - collection of data that describe the occurrence of the disease under study. Centers for Disease Control and Prevention (CDC) - central source of epidemiological information in the U.S. Publishes Morbidity and Mortality Weekly Report. Analytical epidemiology - analyzes a particular disease to determine its probable cause. (risk factors, etc.) Morbidity - incidence of specific diseases Experimental epidemiology - makes hypothesis about a particular disease and experiments to test this hypothesis with a group of people. Mortality - number of deaths from these diseases. 27 28 29 30 5 31 6