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

Defining Some Terms PathologyStudy of disease PathologyStudy of disease EtiologyStudy of the cause of a disease EtiologyStudy of the cause of a disease PathogenesisDevelopment of disease PathogenesisDevelopment of disease InfectionColonization of the body by pathogens InfectionColonization of the body by pathogens DiseaseAn abnormal state in which the body is not functionally normally DiseaseAn abnormal state in which the body is not functionally normally

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

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

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

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

Some Normal Flora

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

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

Classifying Infectious Diseases Symptom A change in body function that is felt by a patient as a result of diisease 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. 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. Syndrome A specific group of signs and symptoms that accompany a disease.

Classifying Infectious Diseases Communicable diseasespread from one host to another. Communicable diseasespread from one host to another. Contagious diseaseeasily spread from one host to another. Contagious diseaseeasily spread from one host to another. Noncommunicable diseasenot transmitted from one host to another. Noncommunicable diseasenot transmitted from one host to another.

IncidenceFraction of a population that contracts a disease during a specific time. IncidenceFraction of a population that contracts a disease during a specific time. PrevalenceFraction of a population having a specific disease at a given time. PrevalenceFraction of a population having a specific disease at a given time. Sporadic diseaseDisease that occurs occasionally in a population. Sporadic diseaseDisease that occurs occasionally in a population. Endemic diseaseDisease constantly present in a population. Endemic diseaseDisease constantly present in a population. Epidemic diseaseDisease acquired by many hosts in a given area in a short time. Epidemic diseaseDisease acquired by many hosts in a given area in a short time. Pandemic diseaseWorldwide epidemic. Pandemic diseaseWorldwide epidemic. Occurrence of Disease

Acute diseaseSymptoms develop rapidly Acute diseaseSymptoms develop rapidly Chronic diseaseDisease develops slowly Chronic diseaseDisease develops slowly Subacute diseaseSymptoms between acute and chronic Subacute diseaseSymptoms between acute and chronic Latent diseaseDisease with a period of no symptoms when the patient is infective Latent diseaseDisease with a period of no symptoms when the patient is infective Severity or Duration of a Disease

The Stages of a Disease Figure 14.5

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

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

Contact Contact DirectRequires close association between infected and susceptible host DirectRequires close association between infected and susceptible host IndirectSpread by fomites IndirectSpread by fomites DropletTransmission via airborne droplets DropletTransmission via airborne droplets Transmission of Disease

Figure 14.6a & 8

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

Figure 14.6b, c

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

Figure Relative frequency of nosocomial infections

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% Fungi10%

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

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

The study of where and when diseases occur The study of where and when diseases occur Epidemiology Figure 14.11

Principles of Disease Surveillance

Epidemiology John Snow Mapped the occurrence of cholera in London Ignaz Semmelweis Showed the hand washing decreased the incidence of puerperal fever Florence Nightingale 1858 Showed that improved sanitation decreased the incidence of epidemic typhus

Descriptive Descriptive Collection and analysis of data regarding occurrence of disease Snow Analytical Analytical Comparison of a diseased group and a healthy group Nightingale Experimental Experimental Study of a disease using controlled experiments Semmelweis Case reporting Case reporting Health care workers report specified disease to local, state, and national offices Nationally Notifiable Diseases Nationally Notifiable Diseases Physicians are required to report occurrence Methods

Table 14.7

Collects and analyzes epidemiological information in the U.S. Collects and analyzes epidemiological information in the U.S. Publishes Morbidity and Mortality Weekly Report (MMWR) Publishes Morbidity and Mortality Weekly Report (MMWR) 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 Centers for Disease Control and Prevention (CDC)

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