PRINCIPLES OF DISEASES AND EPIDEMIOLOGY

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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Principles of Disease andEpidemiology

Pathology Study of disease Etiology Study of the cause of a disease

Pathogenesis Development of disease

Infection Colonization of the body bypathogens

Disease An abnormal state in which thebody is not functionally normally




Transient microbiota may be present for days, weeks,

or months

Normal microbiota permanently colonize the host

Symbiosis is the relationship between normalmicrobiota and the host

Normal Microbiota and the Host




In commensalism, one organism is benefited and the

other is unaffected. In mutualism, both organisms benefit.

In parasitism, one organism is benefited at theexpense of the other.

Some normal microbiota are opportunistic pathogens.

Normal Microbiota and the Host:



Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.2

Locations of normal

microbiota on and in

the human body





Microbial antagonism is competition betweenmicrobes.

Normal microbiota protect the host by: occupying niches that pathogens might occupy

producing acids

producing bacteriocins

Probiotics are live microbes applied to or ingested intothe body, intended to exert a beneficial effect.





Koch's Postulatesare used to provethe cause of aninfectious disease.

Koch¶s Postulates

Figure 14.3.1




Koch's Postulatesare used to provethe cause of aninfectious disease.

Koch¶s Postulates

Figure 14.3.2




Classifying Infectious Diseases

Symptom A change in body function that isfelt by a patient as a result of disease

Sign A change in a body that can bemeasured or observed as a resultof disease.

Syndrome A specific group of signs andsymptoms that accompany adisease.




Classifying Infectious Diseases

Communicable disease A disease that is easilyspread from one host toanother.

Contagious disease A disease that is easilyspread from one host toanother.

Noncommunicable disease A disease that is nottransmitted from one hostto another.




Incidence Fraction of a population that

contracts a disease during aspecific time.

Prevalence Fraction of a population havinga specific disease at a given time.

Sporadic disease Disease that occursoccasionally in a population.

Endemic disease Disease constantly present in apopulation.

Epidemic disease Disease acquired by manyhosts in a given area in a shorttime.

Pandemic disease Worldwide epidemic.

Herd immunity Immunity in most of a population.

Occurrence of Disease




Acute disease Symptoms develop rapidly

Chronic disease Disease develops slowly

Subacute disease Symptoms between acute andchronic

Latent disease Disease with a period of no

symptoms when the patient isinactive

Severity or Duration of a Disease




Local infection Pathogens limited to a small areaof the body

Systemic infection An infection throughout the body

Focal infection Systemic infection that began asa local infection

Bacteremia Bacteria in the blood

Septicemia Growth of bacteria in the blood

Extent of Host Involvement




Toxemia Toxins in the blood

Viremia Viruses in the blood

Primary infection Acute infection that causes theinitial illness

Secondary infection Opportunistic infection after aprimary (predisposing) infection

Subclinical disease No noticeable signs or symptoms(inapparent infection)

Extent of Host Involvement




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




The Stages of a Disease

Figure 14.5




Reservoirs of infection are continual sources of infection.

Human ² AIDS, gonorrhea

Carriers may have inapparent infections or latentdiseases

Animal ² Rabies, Lyme disease

Some zoonoses may be transmitted to humans

Nonliving ² Botulism, tetanus

Soil

Reservoirs of Infection




Contact

Direct Requires close association betweeninfected and susceptible host

Indirect Spread by fomites

DropletT

ransmission via airborne droplets

Transmission of Disease





Figure 14.6a & 8




Vehicle Transmission by an inanimate reservoir (food, water)

Vectors Arthropods, especially fleas, ticks, andmosquitoes

Mechanical Arthropod carries pathogen on feet

Biological Pathogen reproduces in vector






Figure 14.6b, c



Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.7, 9

Are acquired as a result of a hospital stay

5-15% of all hospital patients acquire nosocomialinfections

Nosocomial (Hospital-Acquired) Infections



Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.10

Relative frequency of nosocomial infections




Common Causes of Nosocomial Infections

Percentage of nosocomial infections

Percentage resistant toantibiotics

Gram + cocci 34% 28%-87%

Gram ± rods 32% 3-34%

Clostridium difficile 17%

Fungi 10%




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

H antavirus

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

Emerging Infectious Diseases




The study of whereand when diseasesoccur

Epidemiology

Figure 14.11




Epidemiology

John Snow 1848-1849 Mapped the occurrence of cholera in London

Ignaz Semmelweis 1846-1848 Showed the hand washingdecreased the incidence of puerperal fever

Florence Nightingale 1858 Showed that improvedsanitation decreased the

incidence of epidemic typhus




Descriptive Collection and analysis of dataregarding occurrence of disease

Snow

Analytical Comparison of a diseased groupand a healthy group

Nightingale

Experimental Study of a disease using controlledexperiments

Semmelweis

Case reporting Health care workers report specifieddisease to local, state, and national

offices Nationally Notifiable

DiseasesPhysicians are required to reportoccurrence



Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Table 14.7




Collects and analyzes epidemiological information in theU.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 populationin a given time period

Mortality rate - number of deaths from a disease/totalpopulation in a given time

Centers for Disease Control and Prevention (CDC)

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PRINCIPLES OF DISEASES AND EPIDEMIOLOGY