BIO-31: E.4 P.R Quiz: Ch.14

• Chapter 14 covers the principles of disease and epidemiology.

Pathology, Infection and Disease

• Pathology is the study of disease.
• Etiology refers to the cause of a disease.
• Pathogenesis describes the development of a disease.
• Infection is the invasion or colonization of the body by pathogens.
• Disease is an abnormal state when the body does not perform normal functions.

Normal Microbiota

• Normal microbiota are microbes that permanently colonize the host without causing disease under normal conditions.
• Transient microbiota may be present for days, weeks, or months.
• The Human Microbiome Project analyzes the relationships between microbial communities on the body and human health.
• The distribution and composition of normal microbiota are determined by nutrients, physical and chemical factors, host defenses, and mechanical factors.

Microbial Interactions

• Microbial antagonism (competitive exclusion) is a competition between microbes.
• Normal microbiota protect the host by competing for nutrients and producing substances harmful to invading microbes, and affecting pH and available oxygen.
• Symbiosis describes the relationship between normal microbiota and the host.
• Commensalism is a symbiotic relationship where one organism benefits and the other is unaffected.
• Mutualism is a symbiotic relationship where both organisms benefit.
• Parasitism is a symbiotic relationship where one organism benefits at the expense of the other.
• Some normal microbiota can be opportunistic pathogens.

Koch's Postulates

• Koch's postulates establish that the same pathogen must be present in every case of the disease.
• Further states the pathogen must be isolated from the diseased host and grown in pure culture.
• The pathogen from pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal.
• The pathogen must be isolated from the inoculated animal and shown to be the original organism.
• Koch's postulates are use to prove the cuase of an infectious disease.
• Exceptions to Koch's Postulates include when some pathogens can cause several disease conditions or disease only in humans, or when some microbes have never been cultured.

Classifying Infectious Diseases

• Symptoms are changes in body function felt by a patient.
• Signs are changes in a body that can be measured or observed.
• A syndrome is a specific group of signs and symptoms that accompany a disease.
• A communicable disease can spread from one host to another.
• Contagious diseases spread easily and rapidly from one host to another.
• A noncommunicable disease does not spread from one host to another.

Disease Occurrence

• Incidence refers to the number of people who develop a disease during a particular time period.
• Prevalence refers to the number of people who develop a disease at a specified time, regardless of when it first appeared, accounting for both old and new cases.
• Sporadic diseases only occur occasionally.
• Endemic diseases are constantly present in a population.
• Epidemic diseases are acquired by many people in a given area in a short time.
• Pandemic diseases are a worldwide epidemic.

Disease Severity

• Acute disease; symptoms develop rapidly but the disease lasts only a short time.
• Chronic disease; symptoms develop slowly.
• Subacute disease; intermediate between acute and chronic.
• Latent disease; causative agent is inactive for a time but then activates and produces symptoms.
• Herd immunity is when most of a population is immune.

Extent of Host Involvement

• Local infection; pathogens are limited to a small area of the body.
• Systemic (generalized) infection; an infection throughout the body.
• Focal infection; systemic infection that began as a local infection.
• Sepsis is a toxic inflammatory condition from the spread of microbes (especially bacteria) or their toxins, from a focus of infection.
• Bacteremia; bacteria in the blood.
• Septicemia; also known as blood poisoning, is the growth of bacteria in the blood.
• Toxemia; toxins in the blood.
• Viremia; viruses in the blood.
• Primary infection; acute infection that causes the initial illness.
• Secondary infection; opportunistic infection after a primary (predisposing) infection.
• Subclinical disease; no noticeable signs or symptoms (inapparent infection).

Predisposing factors

• Make the body more susceptible to disease.
• These include; gender, inherited traits (such as the sickle cell gene), climate, weather, fatigue, age, lifestyle, nutrition and chemotherapy.

Development of Disease

• Incubation period is the interval between initial infection and first signs and symptoms.
• Prodromal period is the short period after incubation, characterized by early and mild symptoms.
• Period of illness is when the disease is most severe.
• Period of decline is when signs and symptoms subside.
• Period of convalescence is when body returns to its prediseased state.

Reservoirs of Infection

• Reservoirs of infection are continual sources of infection.
• Human reservoirs include carriers with inapparent infections or latent diseases.
• Animal reservoirs include zoonoses, diseases transmitted from animals to humans.
• Nonliving reservoirs include soil and water.

Disease Transmission

• Direct contact transmission requires close association between the infected and a susceptible host.
• Indirect contact transmission spreads to a host by a nonliving object called a fomite.
• Droplet transmission is transmission via airborne droplets less than 1 meter.
• Vehicle transmission occurs through an inanimate reservoir (waterborne, foodborne, or airborne).
• Vectors are arthropods, especially fleas, ticks, and mosquitoes.
• Mechanical transmission occurs when an arthropod carries pathogens on its feet.
• Biological transmission occurs when the pathogen reproduces in the vector and is transmitted via bites or feces.

Healthcare-Associated Infections (HAIs)

• HAIs, also known as nosocomial infections, are acquired while receiving treatment in a health care facility.
• HAIs affect 1 in 25 hospital patients, infecting 2 million per year with 20,000 deaths.
• HAIs result from; microorganisms in the hospital environment, weakened status of the host, and the chain of transmission in a hospital.
• A compromised host is an individual whose resistance to infection is impaired by disease, therapy, or burns.
• HAIs can be controlled by; reducing the number of pathogens through handwashing, disinfecting tubs, cleaning instruments scrupulously, using disposable materials and intubation, or deploying infection control committees.

Emerging Infectious Diseases

• Emerging infectious diseases are diseases that are new, increasing in incidence, or showing a potential to increase in the near future.
• Most are zoonotic, of viral origin, and likely to be vector-borne.
• Contributing factors include genetic recombination of pathogens like E. coli O157 and avian influenza (H5N1). New strains of pathogens, such as Vibrio cholerae O139.
• Widespread antibiotic/pesticide use leading to antibiotic-resistant strains and changes in weather patterns like Hantavirus.
• Transportation; Chikungunya and West Nile virus.
• Ecological disaster/war/ expanding human settlement; Coccidioidomycosis.
• Failure of animal control measures causing Lyme disease and public health failures causing Diphtheria.

Epidemiology

• Epidemiology studies where and when diseases occur and how they are transmitted in populations.
• Epidemiologists determine disease etiology, identify important factors in disease spread, develop disease control methods, and assemble data to outline disease incidence using graphs and charts.
• John Snow (1848–1849) mapped the occurrence of cholera in London.
• Ignaz Semmelweis (1846–1848) showed that handwashing decreased the incidence of puerperal sepsis.
• Florence Nightingale (1858) showed that improved sanitation decreased the incidence of epidemic typhus.
• Descriptive epidemiology; data collection and analysis (Snow).
• Analytical epidemiology; analyzes a disease to determine its cause (Nightingale).
• Experimental epidemiology; involves a hypothesis and controlled experiments (Semmelweis).
• The Centers for Disease Control and Prevention (CDC) collects/analyzes epidemiological information in the United States, and publishes the Morbidity and Mortality Weekly Report (MMWR)
• Morbidity; incidence of a specific notifiable disease and mortality; the deaths from notifiable diseases.
• Notifiable infectious diseases are diseases that physicians are required to report.
• Morbidity rate is the number of people affected relative to the total population, while mortality rate is the number of deaths from a disease relative to the population in a given time.

Clinical Focus: Healthcare-Associated Infections

• Blood cultures grown on mannitol-salt agar are coagulase-positive and gram-positive cocci, identifying Methicillin-resistant Staphylococcus aureus.
• Strain USA100 is 92% of health care strains.
• Strain USA300 is 89% of community-acquired strains.