Medical Technology Department, Faculty of Science, Islamic University-Gaza MB M ICRO B IOLOGY Dr. Abdelraouf A. Elmanama Ph. D Microbiology 2008 Chapter 14 Principles of Disease and Epidemiology

2008 Principles of Disease and Epidemiology PathologyStudy of disease EtiologyStudy of the cause of a disease PathogenesisDevelopment of disease InfectionColonization of the body by pathogens DiseaseAn abnormal state in which the body is not functionally normally

2008 Transient microbiota may be present for days, weeks, or months Normal microbiota permanently colonize the host Symbiosis is the relationship between normal microbiota and the host Normal Microbiota and the Host

2008 In commensalism, one organism is benefited and the other is unaffected. In mutualism, both organisms benefit. In parasitism, one organism is benefited at the expense of the other. Some normal microbiota are opportunistic pathogens. Normal Microbiota and the Host:

2008 Figure 14.2 Locations of normal microbiota on and in the human body Normal Microbiota and the Host:

2008 Microbial antagonism is competition between microbes. 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. Normal Microbiota and the Host:

2008 Koch's Postulates are used to prove the cause of an infectious disease. Koch’s Postulates Figure

2008 Koch's Postulates are used to prove the cause of an infectious disease. Koch’s Postulates Figure

2008 Classifying Infectious Diseases SymptomA change in body function that is felt by a patient as a result of disease SignA change in a body that can be measured or observed as a result of disease. SyndromeA specific group of signs and symptoms that accompany a disease.

2008 Classifying Infectious Diseases Communicable diseaseA disease that is easily spread from one host to another. Contagious diseaseA disease that is easily spread from one host to another. Noncommunicable diseaseA disease that is not transmitted from one host to another.

2008 IncidenceFraction of a population that contracts a disease during a specific time. PrevalenceFraction of a population having a specific disease at a given time. Sporadic diseaseDisease that occurs occasionally in a population. Endemic diseaseDisease constantly present in a population. Epidemic diseaseDisease acquired by many hosts in a given area in a short time. Pandemic diseaseWorldwide epidemic. Herd immunityImmunity in most of a population. Occurrence of Disease

2008 Acute diseaseSymptoms develop rapidly Chronic diseaseDisease develops slowly Subacute diseaseSymptoms between acute and chronic Latent diseaseDisease with a period of no symptoms when the patient is inactive Severity or Duration of a Disease

2008 Local infectionPathogens limited to a small area of the body Systemic infectionAn infection throughout the body Focal infectionSystemic infection that began as a local infection BacteremiaBacteria in the blood SepticemiaGrowth of bacteria in the blood Extent of Host Involvement

2008 ToxemiaToxins in the blood ViremiaViruses in the blood Primary infectionAcute infection that causes the initial illness Secondary infectionOpportunistic infection after a primary (predisposing) infection Subclinical diseaseNo noticeable signs or symptoms (inapparent infection) Extent of Host Involvement

2008 Make the body more susceptible to disease Short urethra in females Inherited traits such as the sickle-cell gene Climate and weather Fatigue Age Lifestyle Chemotherapy Predisposing Factors

2008 The Stages of a Disease Figure 14.5

2008 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 Reservoirs of Infection

2008 Contact DirectRequires close association between infected and susceptible host IndirectSpread by fomites DropletTransmission via airborne droplets Transmission of Disease

2008 Transmission of Disease Figure 14.6a & 8

2008 VehicleTransmission by an inanimate reservoir (food, water) VectorsArthropods, especially fleas, ticks, and mosquitoes MechanicalArthropod carries pathogen on feet BiologicalPathogen reproduces in vector Transmission of Disease

2008 Transmission of Disease Figure 14.6b, c

2008 Figure 14.7, 9 Are acquired as a result of a hospital stay 5-15% of all hospital patients acquire nosocomial infections Nosocomial (Hospital-Acquired) Infections

2008 Figure Relative frequency of nosocomial infections

2008 Common Causes of Nosocomial Infections Percentage of nosocomial infections Percentage resistant to antibiotics Gram + cocci34%28%-87% Gram – rods32%3-34% Clostridium difficile17% Fungi10%

2008 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 Emerging Infectious Diseases

2008 Contributing factors: Modern transportation West Nile virus Ecological disaster, war, expanding human settlement Coccidioidomycosis Animal control measures Lyme disease Public Health failure Diphtheria Emerging Infectious Diseases

2008 The study of where and when diseases occur Epidemiology Figure 14.11

2008 Epidemiology John Snow Mapped the occurrence of cholera in London Ignaz Semmelweis Showed the hand washing decreased the incidence of puerperal fever Florence Nightingale1858Showed that improved sanitation decreased the incidence of epidemic typhus

2008 DescriptiveCollection and analysis of data regarding occurrence of disease Snow AnalyticalComparison of a diseased group and a healthy group Nightingale ExperimentalStudy of a disease using controlled experiments Semmelweis Case reportingHealth care workers report specified disease to local, state, and national offices Nationally Notifiable Diseases Physicians are required to report occurrence

2008 Table 14.7

2008 Collects and analyzes epidemiological information in the U.S. 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)