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Epidemiology

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The study of the occurrence and spread of diseases within groups of humans, and the methods by which we can limit the spread of pathogens

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Symbiosis

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to live together

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Mutualism

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both members benefit from their interactions. Relationship is beneficial to microbe and human alike, but is not required by either.

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Commensalism

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one member of the relationship benefits without significantly affecting the other. An absolute example is is difficult to prove because the host may experience unobserved benefits

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Parasitism

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A parasite derives benefit from its host while harming it, though some hosts sustain only slight damage. A parasite that allows its hosts to survive are more likely to spread. Hosts that tolerate a parasite are more likely to reproduce.

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Pathogen

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Any parasite that causes disease

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Normal Microbiota

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"Normal Flora" or "Indigenous Microbiota" The microbes that colonize the surfaces of the body without normally causing disease. Two types: resident and transient

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Resident Microbiota

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Remain a part of the normal microbiota of a person throughout life. Found on the skin and on the mucous membranes of the digestive tract, upper respiratory tract, distal portion of urethra and vagina. Most are commensal: they feed on excreted cellular wastes and dead cells without causing harm

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Transient Microbiota

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remain in the body for only a few hours, days or months before disappearing. Found in the same locations as resident members, but cannot persist because of competition from other microorganisms, elimination by the body's defenses, or chemical and physical changes in the body that dislodge them

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Acquisition of Normal Microbiota

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Began to develop when amniotic membrane ruptured and microorganisms came in contact with you during birth. Entered mouth and nose as you passed through birth canal and you breath. And continue to accumulate. Most of the resident microbiota was initially established during the first months of life

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Opportunistic Pathogens

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"opportunists" Microoorganisms that cause disease when the immune system is suppressed, when microbial antagonism is reduced, or when introduced into an abnormal area of the body

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Conditions that create opportunities for pathogens

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1. Introduction of a member of the normal microbiota into an unusual site in the body 2. Immune Suppression 3. Changes in the normal microbiota

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Microbial antagonism/Microbial competition

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Normal condition in which established microbiota use up available nutrients and space, reducing the ability of arriving pathogens to colonize

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Introduction of a member of the normal microbiota into an usual site in the body (Opportunistic Pathogens)

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If a member of the normal microbiota in one site is introduced into a site it normally does not inhabit, the organism may become an opportunistic pathogen Ex. E.Coli in colon is mutualistic, in urethra it causes disease

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Immune Suppression (Opportunistic Pathogens)

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Anything that suppresses the body's immune system (disease, malnutrition, stress, age, chemo) can enable opportunistic pathogens.

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Changes in the normal microbiota (Opportunistic Pathogens)

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Changes in relative abundance of normal microbiota may allow a member of the normal microbiota to become an opportunistic pathogen and thrive.

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Reservoirs of infection

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Sites where pathogens are maintained as a source of infection. Three types: animal, human, nonliving

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Zoonoses

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diseases that spread naturally from their usual animal hosts to humans. Over 150 including, yellow fever, anthrax, bubonic plague, rabies. Humans are usually dead-end hosts; transmission favors movement from animals to humans but not in the opposite direction

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Human Carrier

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Continuous human source of infection People with no obvious symptoms before or after an obvious disease may also be infective in some cases. Some remain both asymptomatic and infective for years (AIDS, syphilis)

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Nonliving Reservoirs

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Soil, water and food can be non living reservoirs. Soil, especially if fecaly contaminated, can harbor bacteria (botulism, tetanus) Water can be contaminated with feces & urine (parasitic worms, pathogenic protozoa, bacteria, viruses) Meats & vegetables, Milk

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Contamination

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refers to the mere presence of microbes in or on the body.

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Infection

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Successful invasion of the body by a pathogenic microorganism. An infection may or may not result in disease; that is, it may not adversely affect the body.

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Portal of Entry

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Several sites where pathogens enter the body. Three major types: the skin, mucous membranes, and the placenta. Parenteral route: way of circumventing usual portals. Involves a puncture through the skin.

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The Skin (Portal of Entry)

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Pathogens can enter through natural openings such as hair follicles and sweat glands. Abrasions, cuts, bites, scrapes, stab wounds, and surgeries open the skin. Larvae of some parasitic worms can burrow through the skin. Some fungi can digest the dead outer layers.

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Mucous Membranes (Portal of Entry)

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line all the body cavities open to the outside. Respiratory tract, pathogens enter the mouth and nose in air. Many viruses enter through eyes by contaminated fingers. Through the GI mucous membranes, these parasites are able to survive the acidic pH and digestive juices. Prions enter through oral cavity.

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Placenta

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About 2% of pregnancies, pathogens cross the placenta and infect the embryo or fetus, causing miscarriage, birth defects or premature.

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Parenteral Route

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means by which portals of entry can be circumvented. Pathogens must be deposited directly into tissues beneath the skin or mucous membranes, ex. punctures by nail or needle.

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Adhesion & Adhesion Factors

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Process by which microorganisms attach themselves to cells. Found on viruses and some bacteria. Viral or bacterial ligands bind to host cell receptors. Interaction can determine host cell specificity. To accomplish adhesion, are either specialized structures or attachment proteins. Prevention of these and adhesion can prevent infection

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Avirulent

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Bacterial cells and viruses that have lost the ability to make ligands--whether as the result of some genetic change (mutation) or exposure to certain physical or chemical agents--become harmless

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Biofilm

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Some bacterial pathogens do not attach to host cells directly, but instead interact with each other to form a sticky web of bacteria and polysaccharides which adheres to a surface within a host. Ex. dental plaque.

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Disease

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All parasites injury their hosts, when the injury is significant enough to interfere with the normal functioning of the body it is disease. Also known as morbidity, is any change from a state of health.

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Infection vs. Disease

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Infection is the invasion of a pathogen, disease results only if the pathogen multiplies sufficiently to adversely affect the body.

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Symptoms Vs. Signs

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Symptoms are subjective characteristics of a disease that can be felt by the patient alone. Signs are objective manifestations of disease that can be observed or measured by others. Sometimes pairs of symptoms and signs reflect the same cause, ex. nausea (symptom) vomiting (sign)

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Syndrome

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group of symptoms and signs that collectively characterizes a particular disease or abnormal condition. Ex. AIDS (acquired immunodeficiency syndrome).

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Asymptomatic/Subclinical

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infections that go unnoticed because they have no symptoms. Even though these infections lack symptoms, in some cases certain signs may still be detected if proper tests are performed.

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Hereditary Disease

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disease genetically transmitted from parents to offspring

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Congenital Disease

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diseases that are present at birth, regardless of cause.

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Degenerative Disease

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Result from aging

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Nutritional Disease

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result from lack of some essential nutrients in diet

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Endocrine (Hormonal) Disease

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Due to excesses or deficiencies of hormones

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Mental Disease

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Emotional or psychosomatic

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Immunological Disease

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Hyperactive or hypoactive immunity

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Neoplastic (Tumor) Disease

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abnormal cell growth

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Infectious Disease

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Caused by infectious agent

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Iatrogenic Disease

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Caused by medical treatment or procedures; are a subgroup of hospital-acquired diseases. ex.. surgical error, yeast infection from antibiotics

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Idiopathic Disease

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Unknown Cause. Ex. alzheimer's disease and MS (multiple sclerosis)

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Nosocomial Disease

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disease acquired in health care setting. Pseudomonos-infection in burn patient.

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Terminology of Disease

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Carino- = Cancer Col-/Colo- = Colon Dermato- = Skin -emia = pertaining to the blood Endo- = inside -gen/gen- = give rise to hepat- = liver Idio- = unknown -itis= inflammation -oma = tumor/swelling -osis = condition of -patho/patho- = abnormal septi = rotting, refers to presence of pathogens terato- = defects tox- = poisin

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Etiology

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study of the cause of a disease

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Germ Theory of Disease

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Proposed by Louis Pasteur, Robert Koch and other microbiologists. States that disease is caused by infections of pathogenic microorganisms.

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Koch Postulates

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Series of essential conditions that scientists must demonstrate or satisfy to prove that a particular microbe is pathogenic and causes a particular disease 1. the suspected agent must be present in every case of the disease 2. That agent must be isolated and grown in pure culture 3. The cultured agent must cause the disease when it is inoculated into a healthy, susceptible experimental host. 4. The same agent must be reisolated from the diseased experimental host

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Pathogenicity & Virulence

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-The ability of a microorganism to cause disease is termed pathogenicity, and the degree of pathogenicity is virulence. -Virulence is the relative ability of a pathogen to infect a host and cause disease. Factors: adhesion factors, biofilms, extracellular enzymes, toxins, antiphagocytic factors

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Exceptions to Koch's Postulates

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-Some pathogens cannot be cultured in the lab -Some diseases are caused by a combination of pathogens, or by a combination of a pathogen and physical, environmental, or genetic cofactors. -Ethical considerations prevent applying them to diseases and pathogens that occur in humans only, cannot inoculate a healthy host -Not possible to establish a single cause for some infectious diseases (pneumonia, meningitis), caused by more than one pathogen -Some pathogens have been ignored

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Virulence Factors

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Pathogens have a variety of traits that interact with a host and enable the pathogen to enter a host, adhere to host cells, gain access to nutrients, and escape detection or removal by the immune system. These pathogens have one or more factors that non-virulent microbes lack

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Hyaluronidase & collagenase

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Extracellular enzyme. degrade specific molecules to enable bacteria to invade deeper tissues. -hyaluronidase digests hyaluronic acid, the "glue" that holds animal cells together -Collagenase breaks down collagen, body's chief structural protein

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Coagulase

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Extracellular Enzyme Causes blood proteins to clot, providing a "hiding place" for bacteria within a clot

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Kinases

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Extracellular Enzyme Digest blood clots, allowing subsequent invasion of damaged tissues ex. staphylokinase and strepokinase

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Toxins

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chemicals that either harm tissues or trigger host immune responses that cause damage.

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Toxemia

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Toxins enter the bloodstream and are carried to other parts of the body, including sites that may be far removed from the site of infection. -Two Types: exotoxins and endotoxin

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Exotoxins

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central to their pathogenicity in that they destroy host cells or interfere with host metabolism. Ex. S. Aureus, clostridia, E.coli, salmonella enterica, shigella

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Cytotoxin

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Exotoxin which kills host cells in general or affect their function

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Neurotoxins

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Exotoxins which specially interfere with nerve cell function

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Enterotoxins

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Exotoxins which affect cells lining the GI tract

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Antitoxins

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protective molecules called antibodies that bind to specific toxins and neutralize them. Immunizations composed of toxoids, toxins treated with heat, formaldehyde, chlorine or other chemicals to make them nontoxic, stimulate production of antibodies

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Endotoxin

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Also called Lipid A. Lipid portion of the membrane's lipopolysaccharide. Can be released when gram-negative bacteria divide, die or are digested. Many times stimulating the body to release chemicals that cause fever, inflammation, diarrhea, hemorrhaging, shock and blood coagulation

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Disease Process

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sequence of events following exposure and infection. Many infectious disease have 5 states: incubation period, prodromal period, illness, decline and convalescence. -A patient is likely to be infectious during every stage of disease

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Incubation Period

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the time between infection and occurrence of the first symptoms or signs of disease. -length depends on virulence of infective agent, infective dose (initial # of pathogens), patient's immune system, nature of pathogen, reproduction time & site of infection

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Prodromal Period

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short time of generalized, mild symptoms that precedes illness. Not all infectious disease have a prodromal stage.

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Illness Period

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Most severe stage of an infectious disease. Signs & symptoms are most evident during this time. Patient's immune system has not yet fully responded to the pathogens, and their presence is harming the body. Usually when patient first goes to doctor.

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Decline Period

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the body gradually returns to normal as the patient's immune response and/or medical treatment vanquish the pathogens. Signs & symptoms subside. Immune system peaks. No recovery means disease is fatal.

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Convalescence Period

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the patient recovers from the illness; tissues are repaired and returned to normal. Length depends on amount of damage, nature of pathogen, site of infection, overall health.

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Portals of Exit

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pathogens must leave infected patients through portals of exit in order to infect others. Many are identical to their counterparts. Often exit hosts in materials that the body secretes or excretes.

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Contact Transmission

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Spread of pathogens from one host to another by direct contact (person to person), indirect contact (fomites) or respiratory droplets (droplets of mucus) droplets can be contact or airborne

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Fomites

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inanimate objects that are inadvertently used to transfer pathogens to new hosts. Ex. needles, toothbrushes, toys, money, bedsheets, etc.

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Vehicle Transmission

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spread of pathogens via, air, drinking water, and food, as well as bodily fluids being handled outside the body

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Airborne Transmission

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involves the spread of pathogens farther than 1 meter to the respiratory mucous membranes of a new host via an aerosol

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Aerosol

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cloud of small droplets and solid particles suspended in the air. May contain pathogens either on dust or inside droplets. Sneezing/coughing or air conditioning, sweeping.

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Waterborne Transmission

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Important in the spread of many GI diseases, Water can be reservoir or vehicle.

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Fecal-Oral Infection

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major source of disease in the world. Some are shed in feces, enter through the GI mucous membrane or skin & cause disease elsewhere in the body

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Foodborne Transmission

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pathogens in and on foods that are inadequately processed, undercooked, or poorly refrigerated.

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Bodily fluid transmission

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blood, urine, saliva and other bodily fluids can contain pathogens. Special care must be taken to prevent such fluids from contacting the conjunctiva or breaks in skin or mucous membrane.

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Vectors

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Animals that transmit diseases from one host to another. Either biological or mechanical.

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Biological Vectors

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not only transmit pathogens, they also serve as hosts for the multiplication of a pathogen during some stage of the pathogen's life cycle. Ex. ticks, lice, fleas, mites. After pathogens replicate within a biological vector, often in its gut or salivary gland, the pathogens enter a new host through a bite. Bite becomes contaminated with the vector's feces or the vectors bite directly introduces pathogens into the new host

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Mechanical Vectors

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not required as hosts by the pathogens they transmit. Only passively carry pathogens to new hosts on their feet or other body parts. houseflies and cockroaches

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Acute Disease

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A disease that develops rapidly but lasts a relatively short time. ex. common cold

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Chronic Disease

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A disease that develops slowly (usually with less severe symptoms) are are continual or recurrent. ex. hepatitis C, TB & leprosy

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Subacute Diseases

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Diseases that have durations and severities that lie somewhere between acute and chronic. Ex. subacute bacterial endocarditis

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Latent Diseases

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Diseases in which a pathogen remains inactive for a long period of time before becoming active. Ex. herpes

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Communicable Disease

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when an infectious disease comes from another infected host, either directly, or indirectly. Ex. flu, herpes, TB If it is easily transmitted between hosts it is contagious

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Noncommunicable Diseases

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Diseases that arise outside of hosts or from normal microbiota. They are not spread from one host to another, and diseased patients are not a source of contamination for others. Ex. Tooth decay & tetanus

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Incidence

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the number of new cases of a disease in a give area or population during a given period of time

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Prevalence

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the totally number of cases, both new and already existing, in a given area or population during a given period of time. Cumulative number.

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Endemic

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A disease that normally occurs continually (at moderately regular intervals) at a relatively stable incidence within a given population or geographical area

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Sporadic

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A disease where only a few scattered cases occur within an area or population.

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Epidemic

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Whenever a disease occurs at a greater frequency than is usual for an area or population. Does not have to infect thousands or millions. Number of cases or time period are not specified. Important factor is that there are more cases than historical stats expect

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Pandemic

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When an epidemic occurs simultaneously on more than one continent

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Local infection/Systemic Infection/Focal Infection

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Li: Infection confined to a small region of the body Si: widespread infection in many systems of the body; often travels in the blood or lymph Fi: Infection that serves as a source of pathogens for infections at other sites in the body

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Primary/Secondary Infection

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Pi: Initial infection within a given patient Si: Infections that follow a primary infection; often by opportunistic pathogens

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Descriptive Epidemiology

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involves the careful tabulation of date concerning a disease. Relevant information includes the location and time of cases of the disease, as well as patient info.

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Index Case

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the first case of the disease in a given area or population. Can be difficult or impossible.

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Analytical Epidemiology

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-investigates a disease in detail, including analysis of data acquired in descriptive epidemiological studies, to determine the probable cause, mode of transmission, and possible means of prevention. -May be used in situations where Koch's postulates are unethical

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Experimental Epidemiology

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Involves testing a hypothesis concerning the cause of disease. Also involves studies to test a hypothesis resulting from an analytical study such as the efficacy of a preventative measure or certain treatment.

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Nosocomial infections/Diseases

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-Infections are those acquired by patients or health care workers while they are in health care facilities. 10% of American patients each year -Diseases are those acquired in a health care setting. Increase the duration and cost of medical care and result in 90,000 annual deaths

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Exogenous/Iatrogenic/Endogenous Nosocomial Infections

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Ex-Infections which are caused by pathogens acquired from the health care environment. Ia-Doctor induced. Are a subset of nosocomial infections that are the direct result of modern medical procedures, ex. catheters, surgery En-Infections that arise from normal microbiota within the patient that become pathogens because of factors within the health care setting.

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Factors Influencing Nosocomial Infections

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-Exposure numerous pathogens present in the health care setting -the weakened immune systems of patients who are ill, making them more susceptible to opportunistic pathogens -Transmission of pathogens among patients and health care workers

Chapter 14-Infection, Infectious Diseases & Epidemiology – Flashcards

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