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Principles of Disease and Epidemiology How do we know you are sick let alone that its an epidemic? 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 Symbiosis • Symbiosis is the relationship between organisms living together • Commensalism • • • Mutualism • • one organism is benefited the other is unaffected. both organisms benefit. Parasitism • one organism is benefited at the expense of the other. 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. Normal Microbiota and the Host: • Locations of normal microbiota on and in the human body Figure 14.2 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. Some Normal Flora Koch’s Postulates Koch's Postulates are used to prove the cause of an infectious disease. Figure 14.3.1 Koch’s Postulates Koch's Postulates are used to prove the cause of an infectious disease. Figure 14.3.2 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. 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. Occurrence of Disease Incidence Prevalence Sporadic disease Endemic disease Epidemic disease Pandemic disease Fraction of a population that contracts a disease during a specific time. Fraction of a population having a specific disease at a given time. Disease that occurs occasionally in a population. Disease constantly present in a population. Disease acquired by many hosts in a given area in a short time. Worldwide epidemic. Severity or Duration of a Disease Acute disease Chronic disease Subacute disease Latent disease Symptoms develop rapidly Disease develops slowly Symptoms between acute and chronic Disease with a period of no symptoms when the patient is infective The Stages of a Disease Figure 14.5 Reservoirs of Infection Reservoirs of infection are continual sources of infection. Human — AIDS, gonorrhea Animal — Rabies, Lyme disease Carriers may have inapparent infections or latent diseases Some zoonoses may be transmitted to humans Nonliving — Botulism, tetanus Soil Reservoirs of Infection Reservoirs of infection are continual sources of infection. Human — AIDS, gonorrhea Animal — Rabies, Lyme disease Carriers may have inapparent infections or latent diseases Some zoonoses may be transmitted to humans Nonliving — Botulism, tetanus Soil Transmission of Disease Contact Direct Indirect Droplet Requires close association between infected and susceptible host Spread by fomites Transmission via airborne droplets Transmission of Disease Figure 14.6a & 8 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 Transmission of Disease Figure 14.6b, c 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 Relative frequency of nosocomial infections Figure 14.10 Common Causes of Nosocomial Infections Percentage of nosocomial infections Percentage resistant to antibiotics Gram + cocci 34% 28%-87% Gram – rods 32% 3-34% Clostridium difficile 17% Fungi 10% 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 Inappropriate use of antibiotics and pesticides V. cholerae O139 Antibiotic resistant strains Changes in weather patterns Hantavirus Emerging Infectious Diseases Contributing factors: Modern transportation Ecological disaster, war, expanding human settlement Coccidioidomycosis Animal control measures West Nile virus Lyme disease Public Health failure Diphtheria Epidemiology The study of where and when diseases occur Figure 14.11 Principles of Disease Surveillance www.who.int/emc/slideshows/Survintro/sld001.htm Epidemiology John Snow 1848-1849 Mapped the occurrence of cholera in London Ignaz Semmelweis 1846-1848 Showed the hand washing decreased the incidence of puerperal fever Florence Nightingale 1858 Showed that improved sanitation decreased the incidence of epidemic typhus Methods • Descriptive Collection and analysis of data regarding occurrence of disease Snow • Analytical Comparison of a diseased group and a healthy group Nightingale • Experimental Study of a disease using controlled experiments Semmelweis • Case reporting Health care workers report specified disease to local, state, and national offices • Nationally Notifiable Diseases Physicians are required to report occurrence Table 14.7 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 CDC and MMWR Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report Published by the CDC Weekly information on reportable diseases