Principles of Disease and Epidemiology

1. Principles of Disease and Epidemiology How do we know you are sick let alone that its an epidemic?

2. Defining Some Terms • Pathology Study of disease • Etiology Study of the cause of a disease • Pathogenesis Development of disease • Infection Colonization of the body by pathogens • Disease An abnormal state in which the body is not functionally normally

3. Symbiosis • Symbiosis is the relationship between organisms living together • Commensalism • one organism is benefited • the other is unaffected. • Mutualism • both organisms benefit. • Parasitism • one organism is benefited at the expense of the other.

4. You as Ecosystem • Transient microbiota may be present for days, weeks, or months • Normal microbiota permanently colonize the host • Some normal microbiota are opportunistic pathogens.

5. Normal Microbiota and the Host: • Locations of normal microbiota on and in the human body Figure 14.2

6. Normal Microbiota and the Host: Normal microbiota protect the host by: • occupying niches that pathogens might occupy • producing acids • producing bacteriocins • Probiotics are live microbes applied to or ingested into the body, intended to exert a beneficial effect.

7. Some Normal Flora

8. Koch’s Postulates • Koch's Postulates are used to prove the cause of an infectious disease. Figure 14.3.1

9. Koch’s Postulates • Koch's Postulates are used to prove the cause of an infectious disease. Figure 14.3.2

10. Classifying Infectious Diseases • Symptom A change in body function that is felt by a patient as a result of diisease • Sign A change in a body that can be measured or observed as a result of disease. • Syndrome A specific group of signs and symptoms that accompany a disease.

11. Classifying Infectious Diseases • Communicable disease spread from one host to another. • Contagious disease easily spread from one host to another. • Noncommunicable disease not transmitted from one host to another.

12. Occurrence of Disease • Incidence Fraction of a population that contracts a disease during a specific time. • Prevalence Fraction of a population having a specific disease at a given time. • Sporadic disease Disease that occurs occasionally in a population. • Endemic disease Disease constantly present in a population. • Epidemic disease Disease acquired by many hosts in a given area in a short time. • Pandemic disease Worldwide epidemic.

13. Severity or Duration of a Disease • Acute disease Symptoms develop rapidly • Chronic disease Disease develops slowly • Subacute disease Symptoms between acute and chronic • Latent disease Disease with a period of no symptoms when the patient is infective

14. The Stages of a Disease Figure 14.5

15. Reservoirs of Infection • Reservoirs of infection are continual sources of infection. • Human — AIDS, gonorrhea • Carriers may have inapparent infections or latent diseases • Animal — Rabies, Lyme disease • Some zoonoses may be transmitted to humans • Nonliving — Botulism, tetanus • Soil

16. Reservoirs of Infection • Reservoirs of infection are continual sources of infection. • Human — AIDS, gonorrhea • Carriers may have inapparent infections or latent diseases • Animal — Rabies, Lyme disease • Some zoonoses may be transmitted to humans • Nonliving — Botulism, tetanus • Soil

17. Transmission of Disease • Contact • Direct Requires close association between infected and susceptible host • Indirect Spread by fomites • Droplet Transmission via airborne droplets

18. Transmission of Disease Figure 14.6a & 8

19. Transmission of Disease • Vehicle Transmission by an inanimate reservoir (food, water) • Vectors Arthropods, especially fleas, ticks, and mosquitoes • Mechanical Arthropod carries pathogen on feet • Biological Pathogen reproduces in vector

20. Transmission of Disease Figure 14.6b, c

21. Nosocomial (Hospital-Acquired) Infections • Are acquired as a result of a hospital stay • 5-15% of all hospital patients acquire nosocomial infections Figure 14.7, 9

22. Relative frequency of nosocomial infections Figure 14.10

23. Common Causes of Nosocomial Infections

24. Emerging Infectious Diseases • Diseases that are new, increasing in incidence, or showing a potential to increase in the near future. • Contributing factors: • Evolution of new strains • V. cholerae O139 • Inappropriate use of antibiotics and pesticides • Antibiotic resistant strains • Changes in weather patterns • Hantavirus

25. Emerging Infectious Diseases • Contributing factors: • Modern transportation • West Nile virus • Ecological disaster, war, expanding human settlement • Coccidioidomycosis • Animal control measures • Lyme disease • Public Health failure • Diphtheria

26. Epidemiology • The study of where and when diseases occur Figure 14.11

27. Principles of Disease Surveillance • www.who.int/emc/slideshows/Survintro/sld001.htm

28. Epidemiology

29. Methods

30. Table 14.7

31. Centers for Disease Control and Prevention (CDC) • Collects and analyzes epidemiological information in the U.S. • Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov Morbidity: incidence of a specific notifiable disease Mortality: deaths from notifiable diseases Morbidity rate = number of people affected/total population in a given time period Mortality rate - number of deaths from a disease/total population in a given time

32. CDC and MMWR • Centers for Disease Control and Prevention • Morbidity and Mortality Weekly Report • Published by the CDC • Weekly information on reportable diseases