Principles of Disease and Epidemiology 14 Principles of Disease and Epidemiology

Principles of Disease and Epidemiology Pathology: The study of disease Etiology: The study of the cause of a disease Pathogenesis: The development of disease Infection: Colonization of the body by pathogens Disease: An abnormal state in which the body is not functioning normally

Normal Microbiota and the Host 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. Figure 14.1c

Normal Microbiota and the Host Locations of normal microbiota on and in the human body. Table 14.1c

Normal Microbiota and the Host Microbial antagonism is a 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.

Symbiosis Commensalism Mutualism Parasitism Some normal microbiota are opportunistic pathogens.

Koch’s Postulates Koch's postulates are used to prove the cause of an infectious disease. Figure 14.3 (1 of 2)

Koch’s Postulates Figure 14.3 (2 of 2)

Classifying Infectious Diseases Symptom: A change in body function that is felt by a patient 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.

Classifying Infectious Diseases Communicable disease Contagious disease Noncommunicable disease

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. 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.

Reported AIDS cases in the United States Figure 14.4

Obesity Epidemic

Severity or Duration of a Disease Acute disease: Symptoms develop rapidly. Chronic disease: Disease develops slowly. Latent disease: Disease with a period of no symptoms when the patient is inactive.

Extent of Host Involvement Local infection: Pathogens are limited to a small area of the body. Systemic infection: An infection throughout the body. Septicemia: Growth of bacteria in the blood.

Predisposing Factors 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

The Stages of a Disease Figure 14.5

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

Viral and Bacterial Zoonoses Table 14.2 (1 of 3)

Table 14.2 (2 of 3)

Transmission of Disease Contact Direct Indirect: Spread by fomites. Droplet

Transmission of Disease Vehicle: Transmission by an inanimate reservoir (food, water). Vectors: Arthropods, especially fleas, ticks, and mosquitoes. Mechanical Biological

Transmission of Disease Figures 14.7b, 14.8

Table 14.3

Nosocomial (Hospital-Acquired) Infections Are acquired as a result of a hospital stay. 5-15% of all hospital patients acquire nosocomial infections. ~20,000 die as a result per year Figures 14.6b, 14.9

Relative Frequency of Nosocomial Infections Table 14.5

Common Causes of Nosocomial Infections Percentage of Nosocomial Infections Percentage Resistant to Antibiotics Gram + cocci 51% 29-89% Gram – rods 30% 3-32% Clostridium difficile 13% Fungi 6%

Emerging Infectious Diseases (EIDs) Diseases that are new, increasing in incidence, or showing a potential to increase in the near future. Contributing factors Genetic recombination E. coli 0157, Avian influenza (H5N1) Evolution of new strains V. cholerae 0139 Inappropriate use of antibiotics and pesticides

Emerging Infectious Diseases Changes in weather patterns Malaria Modern Transportation West Nile virus Animal control measures Lyme disease

Epidemiology The study of where and when diseases occur Figure 14.10

Epidemiology John Snow 1848-1849 Mapped the occurrence of cholera in London Ignaz Semmelweis 1846-1848 Showed that hand washing decreased the incidence of puerperal fever Florence Nightingale 1858 Showed that improved sanitation decreased the incidence of epidemic typhus PLAY Animation: Epidemiology

Centers for Disease Control and Prevention (CDC) Morbidity: Incidence of a specific notifiable disease. Mortality: Deaths from notifiable diseases.

Centers for Disease Control and Prevention (CDC) Collects and analyzes epidemiological information in the United States. Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov

“AIDS” to “Gonorrhea”; “Pertussis” to “Streptococcal Toxic Shock Syndrome” Table 14.7 (1 of 2)

“Haemophilus influenzae” to “Mumps”; “Streptococcus pneumonaie” to “Yellow Fever” Table 14.7 (2 of 2)