Principles of Disease and Epidemiology Chapter 14

Chapter 14: Principles of Disease and Epidemiology

• This chapter discusses principles of disease and epidemiology, covering topics like normal microbiota, symbiosis, patterns of disease, predisposing factors, and the spread of infection.

Normal Microbiota

• Transient microbiota are present for days, weeks, or months.
• Normal microbiota permanently colonize the host.
• Symbiosis is the relationship between normal microbiota and the host.
• Commensalism benefits one organism, the other is unaffected.
• Mutualism benefits both organisms.
• Parasitism benefits one organism at the expense of the other.
• Some normal microbiota are opportunistic pathogens.
• Microbial antagonism is a competition between microbes.
• Normal microbiota protect the host by occupying niches that pathogens might occupy, producing acids, and producing bacteriocins.
• Probiotics are live microbes applied to or ingested into the body, intended to exert a beneficial effect, perhaps by competition.

Patterns of Disease

• Predisposing factors make the body more susceptible to disease: short urethra in females, inherited traits (like sickle cell gene), climate, weather, fatigue, age, lifestyle factors (potentially the biggest one), and chemotherapy.
• The stages of a disease include incubation period (no signs or symptoms), prodromal period (mild signs or symptoms), period of illness (most severe signs and symptoms), period of decline (signs and symptoms), and period of convalescence.

Epidemiology

• Epidemiology is the study of where and when diseases occur.
• Key figures in pioneering epidemiology include John Snow (cholera in London), Ignaz Semmelweis (handwashing and puerperal fever), and Florence Nightingale (sanitation and epidemic typhus).
• Descriptive epidemiology collects and analyzes data. Types include retrospective, prospective, and analytical studies (e.g., Snow's cholera study, Nightingale's study of soldiers during the Crimean War).
• Analytical studies compare a diseased group to a healthy group (e.g., case-control studies, cohort studies).
• Experimental epidemiology involves controlled experiments (e.g. Semmelweis' handwashing study).
• Epidemiology tracks disease occurrence using case reporting systems, nationally notifiable diseases, morbidity (incidence of disease), and mortality (deaths from disease). Also includes morbidity and mortality rates.

Reservoirs of Infection

• Sources of infection include humans (e.g., AIDS, gonorrhoea), or carriers with unapparent infections, and animals (e.g., rabies, Lyme disease), or some zoonotic diseases (animal diseases transmitted to humans). Nonliving reservoirs include soil (botulism, tetanus).

Transmission of Disease

• Transmission can be direct (close association between infected and susceptible host), indirect (spread by fomites – objects that carry disease), droplet (airborne droplets), or via vehicles (food, water, air), or by vectors (arthropods like fleas, ticks, and mosquitoes). Mechanical and biological transmissions are different types of vector transmission.

Nosocomial Infections

• Nosocomial infections are acquired in hospitals.
• Factors contributing to nosocomial infections include microorganisms in the hospital environment and compromised hosts.
• Common causative agents include coagulase-negative staphylococci, S. aureus, Enterococcus, gram-negative rods, and C. difficile.

Emerging Infectious Diseases

• Emerging infectious diseases are new or increasing in incidence.
• Contributing factors include genetic recombination, evolution of new strains, inappropriate use of antibiotics and pesticides creating resistant strains, changes in weather patterns, modern transportation, ecological disasters, and public health failures.
• Examples include avian influenza, E. coli O157, V. cholerae O139, Zika, West Nile virus, Lyme disease, plague, Coccidioidomycosis, hantavirus, and diphtheria.

Check Your Understanding

• Questions are provided in the slides for review.

Explore the key concepts of disease and epidemiology in Chapter 14. This chapter covers the role of normal microbiota, different types of symbiotic relationships, and mechanisms of infection spread. Understand how these factors influence health and disease.