The document discusses key concepts related to the study of disease and epidemiology. It defines important terms like pathology, etiology, pathogenesis, infection, disease, normal flora, opportunistic pathogens, probiotics, and Koch's postulates. It also covers classifications of infectious diseases like endemic, epidemic, pandemic, acute vs chronic diseases. The document outlines the typical development of disease and identifies different reservoirs of infection like human, animal, and non-living reservoirs. It discusses various modes of disease transmission including contact, droplet, vector, and nosocomial transmission. Finally, it touches on emerging infectious diseases and factors that contribute to their emergence.

1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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.

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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)

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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