Chapter 14 Principles of Disease and Epidemiology

Pathology, Infection, and Disease Disease is an abnormal state in which part or all of the body is not properly adjusted or is incapable of performing normal functions. Pathology is the scientific study of disease. Etiology (cause) Pathogenesis (development) Structural and functional changes brought about by disease with their final effects on the body Infection is the invasion and growth of pathogenic microorganisms in the body.

Pathology, Infection, and Disease Infection disease Presence of particular microorganism in part of the body where is not usually found. When a microorganism overcomes the body’s defenses, a state of disease results. Pathogens - disease-causing microorganisms. Pathogenic microorganisms have special properties that allow them to invade the human body or produce toxins. A host is an organism that shelters and supports the growth of pathogens.

Normal Microbiota  Animals, including humans, are usually germfree in utero (used in biology to describe the state of an embryo or fetus ) Microorganisms begin colonization in and on the surface of the body soon after birth Normal microbiota - microorganisms that establish permanent colonies inside or on the body without producing disease. Staphylococcus on epidermis and mucus membranes; Escherichia coli in colon Transient microbiota are microbes that are present for various periods and then disappear. Although these types of organisms may colonize a host and reproduce briefly, the defenses of the human body do not allow them to become permanent.

Relationships Between the Normal microbiota and the Host Symbiosis - living together - long-term interaction between two or more different biological species The three types of symbiosis Normal microbiota and the host exist in symbiosis Opportunistic pathogens Opportunistic pathogens do not cause disease under normal conditions (live in their normal habitat) but cause disease under special conditions. Streptococcus pneumoniae E.coli E.coli (in colon) Synthesize vitamin K Mycobacteria (in the ear) Disease-causing bacteria

Normal Microbiota and the Host Locations of normal microbiota on and in the human body 100 trillion non-pathogenic bacteria/microorganisms that reside in or on a human body Human body is built by 10 trillion cells Human body/Commensal microbiota exist as a community Figure 14.2

Normal Microbiota or Microbiome Microbiome - collective genomes of all the microorganisms (bacteria, fungi and viruses) that reside in a person, literally share our body space

Microbiome and human body environment Microbial community vary at different body sites on the same person (different ecosystem) Bacteria of a specific body site from different persons have more common characteristic (common ecosystem). The microbiome of a healthy and diseased person looks very different (rearranged ecosystem)

Microbiome and metabolic activity Gut microbiome – “forgotten organ” Produce hydrolytic enzymes - help our digestive system – they can vary Synthesize vitamins - B2, B12 and folic acid – slight variation Skin and gut microbiome Stabilize epithelial homeostasis and barrier function Modulate our innate and adaptive immunity Prevent growth of pathogens Production of antimicrobial substances Compete for the nutrients

What is a healthy Microbiome? Who we are ? Microbiome (bacterial Phenotype) Individual genetic material What we eat (diet) Homeostasis Health Low risk of allergies Infection resistance --------------------------------------------- Perturbation Diseases Allergies Metabolic syndrome Obesity Infections What is a healthy Microbiome? One size does NOT fit all - Each person’s microbiome is unique

Relationships Between the Normal Microbiota and other microorganisms Microbial antagonism. Normal microbiota can prevent pathogens from causing an infection by competing for nutrition. Produce substances harmful for invading organisms E. coli produce bacteriocines Affecting condition as pH or available oxygen Cooperation Among Microorganisms  In some situations, one microorganism makes it possible for another to cause a disease or produce more severe symptoms Streptococci that colonize the teeth

How to take care of our “second genome” We are what we eat Probiotics – application of life microbial culture Typically lactic acid producing bacteria ingested to aid digestion and protect intestine from pathogens Prebiotics - refer to chemicals that induce the growth and/or activity of commensal microorganisms Mix of bacteria instead of antibiotics Fecal transplantation Restoration of normal microbiota

The Etiology of Infectious Diseases Koch’s postulates are criteria for establishing that specific microbes cause specific diseases. Koch’s postulates have the following requirements: 1. The same pathogen must be present in every case of the disease; 2. The pathogen must be isolated in pure culture; 3. The pathogen isolated from pure culture must cause the same disease in a healthy, susceptible laboratory animal; 4. The pathogen must be isolated from the inoculated laboratory animal and must be shown to be the original organism

Exceptions to Koch’s Postulates Koch’s postulates are modified to establish etiologies of diseases caused by viruses and some bacteria, which cannot be grown on artificial media. Some diseases have unequivocal signs and symptoms. Tetanus - affects the nervous system and causes painful, uncontrolled muscle spasms Some diseases may be caused by a variety of microbes. Pneumonia and nephritis Some pathogens, cause several different diseases. Streptococcus pyogenes – sore throat, scarlet fiver, skin infections, Certain pathogens, such as HIV, cause disease in humans only.

Classifying Infectious Diseases 1. Patient Appearance Every disease alters body structures and functions A patient may exhibit: Symptoms (subjective changes in body functions) Pain or body discomfort Signs (measurable changes) Fever, swelling, paralysis A physician uses signs to make a diagnosis (identification of the disease) Syndrome - a specific group of symptoms or signs that always accompanies a specific disease

Classifying Infectious Diseases 2. Spreadability Communicable diseases are transmitted from one host to another. Chicken pox, genital herpes, tuberculosis A contagious disease is one that is easily spread from one person to another. Chicken pox Noncommunicable diseases are caused by microorganisms that normally grow outside the human body and are not transmitted from one host to another Tetanus - Clostridium tetani

Classifying Infectious Diseases 3 Classifying Infectious Diseases 3. Occurrence of a Disease  (frequency of occurrence) Sporadic – occur only occasionally in population Typhoid fever Endemic – constantly present in a population Common cold Epidemic – if many people in a given area acquire a certain disease in a relatively short period Influenza Pandemic – An epidemic disease that occurs worldwide Some influenza, AIDS Disease occurrence is reported by: Incidence - Number of new disease cases per population at risk ( indicator of the spread of the disease) Measured over a given time interval Prevalence - Number of current ( old and new) cases per population at risk ( how seriously and how long the disease affects a population) Fraction of a population having a specific disease at a given time Herd immunity is the presence of immunity to a disease in most of the population. Vaccination (immunization) prevent spread of the disease

Classifying Infectious Disease 4. Severity and Duration of a Disease The scope of a disease can be defined as: Acute – develops rapidly but last for short time influenza, common cold Chronic - develop slowly, continual or recurrent for long time tuberculosis Subacute – intermediate between acute and chronic some brain diseases, endocarditis Latent – the causative agent remains inactive for a time but than becomes active to produce symptoms of the disease . shingles

Classifying Infectious Disease 5. Extent of Host Involvement Local infection: Pathogens are limited to a small area of the body abscesses Systemic infection: An infection throughout the body by blood and/or lymph Bacteremia: Bacteria in the blood Sepsis: Toxic inflammatory condition arising from the spread of microbes, especially bacteria or their toxins, from a focus of infection Septicemia: Growth of bacteria in the blood Toxemia: Toxins in the blood Viremia: Viruses in the blood Focal infection: Systemic infection that began as a local infection Local tooth infection can moves via blood or lymph to set up a new infection at another site - rheumatoid arthritis Primary infection: Acute infection that causes the initial illness Secondary infection: Opportunistic infection after the primary infection (predisposing) has weakened the body defense Subclinical infection: No noticeable signs or symptoms (inapparent infection)

Predisposing Factors A predisposing factor is one that makes the body more susceptible to disease or alters the course of a disease. Gender (short urethra in females) Climate and weather Age Fatigue Inadequate nutrition. Inherited traits, such as the sickle-cell anemia (SCA) Chemotherapy  

Patterns of Disease Development of Disease 1. The incubation period is the time interval between the initial infection and the first appearance of signs and symptoms. 2. The prodromal period is characterized by the appearance of the first mild signs and symptoms. 3. During the period of illness, the disease is at its height, and all disease signs and symptoms are apparent. 4. During the period of decline, the signs and symptoms subside. 5. During the period of convalescence, the body returns to its predeceased state, and health is restored.

The Spread of Infection 1. Reservoir of Infection - A continual source of infection Human reservoirs of infection - People who have a disease or are carriers of pathogenic microorganisms. Sick people = actively ill Carriers = one who harbors disease organisms in their body without manifest symptoms (healthy) Latent infection carriers = contagious during incubation period or convalescent period Zoonoses - are diseases that affect wild and domestic animals and can be transmitted to humans. Direct contact with animal or its waste Eating animals Bloodsucking arthropods Nonliving reservoirs - Soil, water, and food can be reservoirs of infection Presence of microorganisms is often due to contamination by feces or urine.

The Spread of Infection 2. Transmission of Disease  Direct contact - involves close physical contact between the source of the disease and a susceptible host. Indirect contact - transmission by fomites (inanimate objects) Vehicle transmission -transmission by a medium such as water, food, or air. Droplet transmission - transmission via saliva or mucus in coughing or sneezing Airborne transmission refers to pathogens carried on water droplets or dust for a distance greater than 1 meter. Arthropod vectors carry pathogens from one host to another mechanical transmission passively carry pathogens on body parts e.g. houseflies biological transmission from bites: usually involves complex life cycle of pathogen cycling between vector and host (e.g. mosquito - malaria)

Nosocomial (Hospital-Acquired) Infections A nosocomial infection is any infection that is acquired during the course of stay in a hospital, nursing home, or other health care facility. (2011) Healthcare-associated infections (HAI) are defined as infections not present and without evidence of incubation at the time of admission to a healthcare setting. About 5 to 15% of all hospitalized patients acquire nosocomial infections (bloodstream infection, pneumonia, and urinary tract infection)

1. Microorganisms in the Hospital environment Certain normal microbiota are often responsible for nosocomial infections when they are introduced into the body through such medical procedures as surgery and catheterization. Opportunistic, drug-resistant bacteria are the most frequent causes of nosocomial infections.

2. Compromised Host  Patients which are the most susceptible to nosocomial infections: burns surgical wounds suppressed immune systems

Chain of Transmission of nosocomial infections Direct contact staff members and patients between patients. Indirect contact Fomites such as catheters, syringes, and respiratory devices Ventilation system - airborne transmission

Control of Nosocomial Infections Aseptic techniques can prevent nosocomial infections. Washing hands before inserting a catheter Proper handling contaminated materials. Hospital infection control staff members are responsible for overseeing the proper cleaning, storage, and handling of equipment and supplies.

Emerging Infectious Diseases Diseases that are new, increasing in incidence, or showing a potential to increase in the near future Contributing factors Genetic recombination E. coli O157, avian influenza (H5N1) Evolution of new strains V. cholerae O139 Inappropriate use of antibiotics and pesticides Antibiotic-resistant strains Changes in weather patterns malaria Modern transportation Spread to new geographic areas Ecological disaster, war, and expanding human settlement Coccidioidomycosis Animal control measures Lyme disease Public health failure Diphtheria

Epidemiology The study of where and when diseases occur when the disease occurs to whom (age, race, class etc.) mode of transmission reservoirs effective methods of control plans to prevent future outbreaks Descriptive epidemiology. collection of data describing the occurrence of disease (affected people, place and period of disease) Analytical epidemiology. A group of infected people is compared with an uninfected group. Experimental epidemiology Controlled experiments designed to test hypotheses are performed.

Epidemiology 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 Nationally notifiable diseases (contagious and/or deadly diseases) Physicians are required to report occurrence of specified disease to local, state, and national offices. Case reporting provides data on incidence and prevalence Morbidity: Incidence of a specific notifiable disease. Morbidity rate: Number of people affected in relation to the total population in a given time period Mortality: Deaths from notifiable diseases Mortality rate: Number of deaths from a disease in relation to the population in a given time

Epidemiology, Epidemiological graphs

Learning objectives Define pathology, etiology, infection, and disease. Define normal and transient microbiota, and microbiom. Compare commensalism, mutualism, and parasitism, and give an example of each. Contrast normal and transient with opportunistic microbes. List Koch’s postulates. Differentiate a communicable from a noncommunicable disease. Categorize diseases according to frequency of occurrence. Categorize diseases according to severity. Define herd immunity. Identify four predisposing factors for disease. Put the following terms in proper sequence in terms of the pattern of disease: period of decline, period of convalescence, period of illness, prodromal period, incubation period. Define reservoir of infection. Contrast human, animal, and nonliving reservoirs, and give one example of each. Explain three methods of disease transmission. Define nosocomial infections and explain their importance. Define compromised host. List several methods of disease transmission in hospitals. Explain how nosocomial infections can be prevented. Define epidemiology and describe three types of epidemiologic investigation. Identify the function of the CDC