Chapter 10: Infection, Infectious Diseases, and Epidemiology
number of ways Diseases can be classified in
How (and if) they are spread to their host, Their extent, Their longevity and severity, Their frequency and geographical distribution
Germ theory of disease
Hypothesis formulated by Pasteur in 1857 that microorganisms are responsible for disease.
Numbers of Invaders & Chances of Infection
If just a few microbes gain entrance into the body, a disease is not likely to occur; Likelihood of disease generally increases with as the number of pathogens increase LD50 : Lethal Dose of a microbes toxin that will kill 50% of experimentally inoculated test animal. ID50 : infectious dose required to cause disease in 50% of inoculated test population. What amount of a toxin causes disease?
Carrier
In human pathology, continuous asymptomatic human source of infection
Signs
In pathology, objective manifestations of a disease that can be measured or observed by others.
Mucous membranes (portal of entry)
Include the lining of body cavities open to the outside world; lining of the respiratory, gastrointestinal, urinary, and reproductive tracts. Tend to be more hospitable for pathogens because they are warm, moist, and relatively thin.
Genitourinary Tract
Includes UTI's and pathogens that are contracted sexually
five stages following infection of infectious disease
Incubation period: time between infection and the first appearance of any signs/symptoms Prodromal: short period of time; characterized by early, mild symptoms of disease (aches, fatigue, etc.) Period of illness: time period when disease is most severe; overt symptoms/signs of disease (fever, muscle pain, sore throat, enlarged lymph nodes, etc.) Period of decline: signs/symptoms subside as immune response/medications take effect Period of convalescence: body returns to pre-diseased state; recovery
5 stages/periods of disease development
Incubation, Prodromal, Illness/Invasive Phase, Decline, and Convalescence(recovery)
Adhesion:
Process by which microorganisms attach themselves to cells Pathogens use adhesion factors to attach to hosts; Includes specialized structures; Suckers on helminths or adhesion disks on protozoa
Exotoxins
Produced within bacteria cell, but secreted outside the cell into the surrounding medium; Exotoxins are proteins; Soluble in water and transported by blood; Exotoxins have a relatively small LD50
Koch's Postulates
Published in 1877: showed that Bacillus anthracis was causative agent of anthrax. Outlined the criteria that need to be met in order to link a specific pathogen to a specific disease
Mutualism
Symbiotic relationship in which both members benefit from their interaction.
Commensalism
Symbiotic relationship in which one member benefits without significantly affecting the other member.
Severity and Longevity of Disease Acute disease:
Symptoms develop rapidly, but lasts a short time e.g., common cold
Diseases may become manifest in different ways:
Symptoms: Subjective characteristics of disease felt only by the patient; Such as pain and tiredness.....feelings. Signs: Objective manifestations of disease observed or measured by others; Such as fever and swelling....measurements. Syndrome: Symptoms and signs that characterize a disease or abnormal condition; example: malaise, loss of helper T cells, diarrhea, weight loss, toxoplasmosis, and tuberculosis characterize AIDS
Adhesion
The attachment of microorganisms to host cells.
Etiology
The study of the causation of disease.
Epidemiology
The study of the occurrence, distribution, and spread of diseases in humans.
Prevalence
The total number of cases of a disease in a given area or population during a given period of time; # of new and old cases/# of people at risk.
Illness
Third stage of disease; Signs and symptoms are most evident during this stage. The body's immune system has not fully responded to pathogens and their presence is harming the body. The stage when a patient is first seen by a physician.
Vehicle Transmission:
Through a medium
Exotoxins
Toxin secreted by a pathogenic microorganism into its environment; Example: clostridia which causes gangrene, botulism, and tetanus.
Enterotoxins
Toxins which affect cells lining the gastrointestinal tract.
Cytotoxins
Toxins which kill host cells or affect their function.
Neurotoxins
Toxins which specifically interfere with nerve cell functions.
Eye Diseases
Trachoma; Chlamydia trachomatis; Conjunctivitis; Pink eye
Airborne transmission
Transmission of pathogens usually occurs when an aerosol is formed from changing linen, dry mopping, or anything that stirs dust. Spread of pathogens to the respiratory mucous membranes of a new host via the air or in droplets carried more than 1 meter.
Droplet
Transmission via airborne droplets of mucus that exit body during exhaling, coughing, and sneezing. example: cold and flu HOWEVER, if droplets travel more than 1 meter, the mode is considered airborne transmission
Common Diseases contracted via the Respiratory Tract
Tuberculosis, Whooping cough, Pneumonia, Measles, Strep Throat, Diphtheria
2 types of flora; Resident flora (microbiota) &Transient flora (microbiota):
remain part of the normal flora of a person through life; mostly commensal remain in the body for only a few hours, days, or months before disappearing; competition from other microbes, body's defense, or chemical/physical changes destroy them
direct contact transmission
requires person-to-person contact; sex,shaking hands
Epidemiology
study of where and when diseases occur and how they are transmitted within populations.
Symptoms versus Signs
subjectively felt by patient / outside observable
Ligands:
surface molecules on bacteria and viruses (attachment sites) that allow them to attach to host cell receptor sites; Often found on fimbriae and glycocalyses of bacteria
pathogenicity
the ability of an organism to incite a disease state.
Decriptive epidemiology
the careful recording of data concerning a disease; it often includes detection of the index case.
sequela
the effects seen even after the recovery of some diseases. Ex: Reyes's syndrome after the flu, encephalitis after the measles, heart valve damage after strep infections.
index case
the first case of the disease in a given area or population
infection
the growth and development of a pathogen on or in a host's body
primary infection
the initial infection in a previously healthy person.
Infection
the invasion of the host by a pathogen
Animal Reservoirs; Zoonoses
Wild and domestic animals; Diseases that can be transmitted from animal host to humans.
symptom
a characteristic of disease that can be observed or felt only by the patient. ex: pain nausea, headache, chills, itching,, abdominal cramps
sign
a characteristic of disease that can be observed or measured when examining a patient. ex.swelling, rash, pulse, pus formation, vomiting, tachycardia, bradycardia.
aerosol
a cloud of small droplets and solid particles suspended in the air.
virulence factors
a collective term used to describe the characteristics of an organism that enable it to invade, colonize, and promote disease in a host.
syndrome
a combination of signs and symptoms that normally occur together.
Which of the following phrases describes a contagious disease?
a disease that is easily passed from host to host in aerosols.
Contagious disease
a disease that is easily transmitted from a reservoir or patient.
zoonosis
a disease that is transmitted from animal to human
Syndrome
a group of symptoms and signs that collectively characterizes a particular abnormal condition.
Pathogenicity
a microorganisms ability to cause disease
super infection
a secondary infection that results from the destruction of normal flora. ex: yeast infection
Kochs Postulates
a series of essential conditions to prove the cause of infectious diseases. Some circumstances can make the use of these postulates difficult or even impossible.
Prodromal Period
a short period during which non-specific symptoms such as malaise and muscle aches appear; not apparent in the course of all diseases.
disease
a situation (that can arise from an infection) in which the state of health of the host is altered in such a way that normal functions cannot be carried out.
commensalism
a symbiosis in which one of the organisms involved benefits, while the other is neutral(unaffected) neither benefited nor harmed; humans have skin, eye, and ear commensals.
mutalism
a symbiotic relationship in which both of the organisms involved benefit; humans have a mutualistic relationship with our intestinal flora.
parasitism
a symbiotic relationship in which one of the organisms(the parasite) benefits at the expense of the other organism(the host); pinworms(helminths)
skin
the largest organ of the body. When unbroken is an effective barrier for most microorganisms.
morbidity rate
the number of cases in relation to the total number of people in the population in a given year; expressed in 1000.
mortality rate
the number of deaths due to a certain disease in relation to the total population in a given year; expressed per 1000.
incidence
the number of new cases seen in a specific period of time.
Toxemia
the presense of poisons called toxins in the blood
The most frequent portal of entry for pathogens is
the respiratory tract
portals of entry
the sites at which microorganisms gain entry to the body and tissues; include: skin , mucous membrane of the digestive, respiratory and urogenital systems, through the placenta, and parenteral route.
portals of exit
the sites at which microorganisms leave the body; usually associated with bodily secretion or feces.
epidemiology
the study of factors and mechanisms involved in the spread of a disease within a certain population.
Etiology
the study of the cause of a disease
etiology
the study of the cause of a disease
Epidemiology:
the study of the location, course, and transmission of diseases within populations; An epidemiologist looks for patterns in disease; age, sex, occupation, lifestyle, socioeconomic status, immunizations, geography; concerned about methods for controlling disease; drugs, vaccines, water treatment, food inspection, personal habitats; concerned about frequency of disease
Incubation Period
the time b/w the onset of exposure and the appearance of signs and symptoms.
Illness/Invasive Phase
the time during which the disease develops its most severe signs and symptoms; fever is an important component of this phase; fever is caused by the production of pyrogens by the pathogens (as well as by the host immune system).
prevalence
the total number of cases at any one time.
Disease:
abnormal body function or deviation from health; "homeostatic imbalance"
Biofilms:
about 65% of all bacterial infections
Nosocomial infections and nosocomial diseases
acquired by patients in health care facilities
Hospital Epidemiology Nosocomial Infections:
acquired by patients or workers in health care facilities; Includes hospitals, dental offices, nursing homes, clinics
non-communicable
acquired from the environment (not spread from one host to another)
exogenous
acquired from the health care environment
Extent of Disease Primary Infection & Secondary Infection
acute infection that causes initial illness infection caused by an opportunistic pathogen after the primary infection has weakened the body's defenses e.g., bacterial pneumonia followed by influenza, e.g., sinus infection following a cold, e.g., yeast infections after antibiotic treatment
The process by which microorganisms attach themselves to cells is
adhesion
Virulence Factors affect the relative ability of a pathogen to infect and cuase disease. What are the factors?
adhesion factors extracellular enzymes toxins antiphagocytic factors
The nature of bacterial capsules
affects the virulence of these bacteria
vehicle transmission
airborne transmission, waterborne transmission, and foodborne transmission.
Which of the following types of epifemiologists is most like a detective?
an analytical epidemiologist
microbial antagonism
an effect where the normal flora populations serve to compete (for space and nutrients) with pathogenic species to inhibit their growth and decrease the probability of disease.
secondary infection
an infection that arises after the primary infection and usually is a result of the primary infection.
Three types of reservoirs
animal reservoirs, Human carriers, Nonliving reservoirs
Antitoxins
antibodies the host forms against toxins
Noncommunicable disease
arise from either outside of hosts or from normal microbiota.
common source epidemic
arises from contact with contaminated substances. ex: food poisoning
propagated epidemic
arises from person-to-person contact. ex: common cold
Infections that may go unnoticed due to the absence of symptoms are called _____ infections.
asymptomatic
When pathogenic bacterial cells lose the ability to make adhesions, they
become avirulent
vector transmission
biological and mechanical vectors.
An animal that carries a pathogen and also serves as host for the pathogen is a ____ vector.
biologocal
congenital
born with it-anatomical and physiological (structural and functional) defects present at birth; caused by drugs (legal and illegal), X-ray exposure, or infections
Severity and Longevity of Latent disease:
causative agent remains inactive for awhile, but then becomes active to produce symptoms e.g., shingles caused by the chicken pox virus
necrotizing factors
cause death to body cells; produced by Group A Strep (GAS): S. pyogenes.
Opportunistic Pathogens
cause disease when the immune system is suppressed, when normal microbial antagonism (competition) is affected by certain changes in the body, and when a member of the normal microbiota is introduced into an area of the body unsual for that microbe.
mixed infection
caused by several species of pathogens that are present at the same time such as dental caries and periodontal diseases.
infectious
causes by microbe or an infectious agent
latent
characterized by periods of inactivity either before symptoms appear or between attacks; most common in viral infections.
Aerosols
clouds of water droplets, which travel more than 1 meter in airborne transmission.
normal flora
collectively refers to all the organisms that permanently associate themselves with the body after birth, and under normal circumstances do not produce disease in the host.
Infection:
colonization of the body by pathogens OR presence of a microbe in a part of the body where it is NOT normally found; infection may or may not result in disease example: carriers can have a pathogen but not feel ill
local infection
confined to a specific area of the body.
focal infection
confined to a specific area, but pathogens from the infection, or their toxins, can spread.
Universal Precautions
consists of policy and procedure guidelines regarding sharp (needle, scalpel) disposal, hand-washing, and safety equipment usage.
An axenic environment is one that
contains only one species
formites
contaminated non-living objects such as needles, toys, toothbrushes,diapers, drinking glasses, bedsheets, medical equipment and money-inanimate objects that are inadvertently used to transfer pathogens to new hosts
Virulence Factors
contribute to the ability of pathogens to invade a host
Virulence
degree of pathogenicity.
The length of incubation
depends of the virulence of the pathogen, the initial number of pathogens, the state and health of the host, and the nature of the pathogen and its reproductive time
endogenous
derived from normal microbiota that become opportunistic while in the hospital setting
chronic
develops more slowly, is usually less severe, but persist for a long period of time.
acute
develops rapidly and runs its course quickly.
Contact transmission
direct and indirect transmissions
Infectious Disease:
disease caused by a pathogen (sometimes called infectious agent)
pathogen
disease causing.
zoonotic diseases (zoonoses)
diseases of animals that may be spread to humans via direct contact with the animal or its waste products, or via an arthropod. Humans may be asymptomatic carriers.
Extent of Disease Subclinical infection:
does not cause noticeable illness, However, person carrying the pathogen can still spread it (healthy carrier)
septic shock
drop in blood pressure
iatrogenic
due to medical treatment or procedures. ex: superinfection
mental
emotional or psychosomatic
coagulase
enzyme that accelerates: clot formation
lecithinase
enzyme that destroys cellular membranes.
The study of where and when diseases occur and how they are transmitted within populations is____.
epidemiology
The study of the cause of a disease is___.
etiology
neoplastic
excessive growth. ex. tumors -abnormal cell growth.
Toxoid
exotoxin that has been inactivated by some chemical means no longer causes disease, but still stimulates the production of antitoxin against the toxin. Toxoids are often important components of vaccines example: DPT vaccine; protects against Diphtheria, Pertussis, and Tetanus; contains diphtheria toxoid and tetanus toxoid
Antiphagoctic factors
factors prevent phagocytosis by the host's phagocytic cells
Nonliving reservoirs of disease, such as a toothbrush, drinking glass, and needle, are called ____
fomites
Transmission
from a reservoir or a portal of exit to another host's portal of entry
Hereditary
genetic-caused by errors in the genetic code received from the parents
nosocomial
healthcare setting acquired
Which of the following are most likely to cause disease?
highly virulent organisms
endocrine
hormones (due to excesses or deficiencies of hormones)
immunological
hyperactive or hypoactive immunity
A patient contracted athletes foot after long term use of a medication. His physician explained that the malady was directly related to the medication. Such infections are termed:
iatrogenic infection
optimal opportunities
immune suppression, changes in the normal microbiota(superinfections), movement of the normal microbiota to a new location.
Morbidity rate:
incidence of disease (number of people affected by disease in given time period)
Disease Process (stages of infectious diseases)
incubation period prodromal period illness decline convalescence
iatrogenic
induced by treatment or medical procedures
Nonliving reservoirs
infection include soil, water, and inanimate objects.
nosocomial infections
infections acquired while in a healthcare facility.( ex: hospital, hospice, nursing homes, doctor/dentist office.)
Communicable disease
infectious disease comes either directly or indirectly from another host.
communicable
infectious diseases that can be easily spread from one host to another (contagious)
neurotoxins
inhibit proper nerve impulse transmission; mechanism of botulism (flaccid paralysis) and tetanus (spastic paralysis).
Vehicle Transmission
involves airborne, waterborne, and foodborne transmission.
parenteral route
involves direct deposition of organisms into the hosts' tissues; ex: punctures, biters, surgery
Eperimental epidemiology
involves testing a hypothesis resulting from analytical studies
endemic disease
is constantly present in the population of a particular geographical area, but the number of cases and the severity of the disease both remain low enough not to constitute a public health problem. ex: chicken pox (prior to vaccine), common cold, allergies.
reasons for notifiable diseases are categorized
it is a zoonosis, sexually transmitted, or routinely immunize against it.
cytotoxins
kill host cells or inhibit their normal function; mechanism of diphtheria and anthrax.
A disease in which a pathogen remains inactive for a long period of time before becoming active is termed a(n)
latent disease
endotoxins
lipid substances produced and released into tissues from the cell walls of Gram-negative organisms as they die and cell wall lysis occurs.
Extent of disease focal infection:
local infection that causes subsequent infection or symptoms in other parts of the body. For example, tetanus(lockjaw) is caused by the release of extoxin from a local infection, perhaps an infected puncture wound of the foot.
3 reservoirs for infection
locations from which pathogens can be spread; Animal reservoirs, Human carriers, and Non-living (Environmental) Reservoirs
Asymptomatic or subclinical infections
may go unnoticed because of the absense of symptoms, even though clinical tests might reveal signs of disease.
Symbiosis
means "to live together" We have symbiotic relationships with countless microorganisms
virulence
measures the intensity of the disease produced.
which of the following is false concerning microbial contaminants?
most microbal contaminants will eventually cause harm
flaccid paralysis
muscles unable to contract. (relaxed)
spastic paralysis
muscles unable to relax (stayed contracted)
In which type of symbiosis do both members benefit from their interaction?
mutualism
Competitive exclusion
no 2 species can simultaneously and continuously occupy the same niche; Thus, normal flora outcompete potentially pathogenic bacteria, protecting their host
Fomites:
non-living object that can transmit disease between hosts. Examples of fomites: bedding, toys, money, thermometers, keyboard, toothbrushes
____ infections are those acquired by patients or staff while in health care facilities.
nosocomial
Epidemiologists track the Incidence/ prevalence of a disease
number of new cases/ total number of cases
Mortality rate:
number of people that died from particular disease in given time period
Control/or Methods of prevention of nosocomial infection(and breaking the chain of transmission)
observance of aseptic technique; frequent hand washing especially between patients; careful handling, cleaning, and disinfection of fomites; where possible use of single-use disposable items; patient isolation; various institutional methods such as air filtration within the hospital; EDUCATION! Prescribe antibiotics only when necessary; avoid invasive procedures if possible
indirect contact transmission
occurs through formites, and droplet transmission.
epidemic disease
occurs when a disease has a sudden, very high incidence in a population; considered a public health problem.
Some microbes can gain entrance thru
openings in the skin:hair follicles and sweat glands; Abrasians and scrapes; Some parasitic worms can burrow thru the skin Some fungi can digest the outer layer of skin
Noraml Microbiota
organisms that live in and on the body. Some are resident and others are transient.
Endotoxins
part of the LPS layer; the Lipid A portion; As such, endotoxins are characteristic of Gram-negative bacteria; Endotoxins are released upon lysis, during reproduction, or are phagocytized Have a relatively large LD50; Endotoxins produce similar effects Fever, inflammation, shock; Antitoxins not generally produced against endotoxins
A microbe that causes disease is called a ___.
pathogen
Extent of disease Local infection:
pathogens are limited to small area of the body
Foodborne:
pathogens in and on foods that inadequately processed, undercooked, or poorly refigerated
Extent of disease Systemic infection:
pathogens or their toxins are spread throughout the body by the blood or the lymph
Doplet Transmission
pathogens travel in droplets of mucus less than 1 meter to a new host as a result of speaking, coughing, or sneezing.
Carriers:
people who carry a pathogen but remain asymptomatic Examples: AIDS, tuberculosis, syphilis
Decline
period when the signs and symptoms begin to subside.
Convalescence(recovery)
period when tissues are repaired, healing takes place, and the body regains strength.
Direct Contact transmission
person-to-person spread by bodily contact.
Notifiable disease:
physicians are required by law to report cases to U.S. Health Official
toxins
poisonous substances produced and released by bacteria.
To total number of cases of a disease in a given area is its ___
prevalence
hemolysins
proteins that enable organisms to degrade red blood cells for access to iron; specifically called streptolysins when produced by the streptococci.
Etiology
refers to the cause of disease. Not ALL diseases are caused by microbes; ex: inherited disorders, obesity
infestation
refers to the growth and development of large pathogens in or on the host. ex. helminths or arthropods
Microbial contamination
refers to the mere presense of microbes in or on the body or object. They include harmless resident and transient members of the microbiota, as well as pathogens, which after a successful invasion cause an infection.
Toxemia
refers to toxins in the bloodstream that are carried beyond the site of infection
Endotoxins (lipid A)
released from the cell wall of dead and dying Gram-negative bacteria and can cause fatal effects.
Notifiable Diseases
those diseases that by law must be reported to public health officials. ex: AIDS, anthrax, botulism, cholera, gonorrhea,mumps, contaminated water,yellow fever, hepatitis, measles, plague, malaria, smallpox,rubella,lyme
degenerative
tissues ie: myopia result from aging
foodborne transmission
transmission of pathogens usually occurs when food has been processed in an unsanitary environment, is incompletely cooked, or was poorly refrigerated.
waterborne transmission
transmission of pathogens usually occurs when the water is untreated or improperly treated. Ex: cholera or hepatitis
idiopathic
unknown agent cause
World Health Organization
use epidemiological data to promulgate rules and standards for clean, potable water and safe food, to prevent disease by controlling vectors and animal reservoirs, and to educate people to make healthy choices concerning the prevention of disease.
Streptokinase -
used to dissolve blood clots in the Heart (heart attacks due to obstructed coronary blood vessels)
antitoxin
what The body produces antitoxins; an antibody designed to bind to a specific toxin; neutralizes toxin, making it harmless
pandemic disease
when an epidemic occurs simultaneously on more than one continent.
biological vector
when the agent of transmission is necessary for the multiplication or development of the microorganism; the vector is not only contaminated, but also infected; ex including: most biting insects like mosquitoes and ticks.
mechanical vector
when the agent of transmission is not necessary for the multiplication or development of the microorganism; only provides a "ride" for the organism; ex include: the legs of flies or cockroaches and contaminated unwashed hands.
bacteremia
where bacteria are simply transported in the blood, but do not multiply.
septicemia
where pathogens are present and multiplying in the blood. (cell division)
toxemia
where toxins are release by pathogens, are present in the blood.
viremia
where viruses are in the blood.
droplet transmission
which occurs when a person in close proximity to others cough, sneezes, or even speaks.
Examples of zoonoses
yellow fever, anthrax, bubonic plague, and rabies.
Diseases that are naturally spread from their usual animal hosts to humans are called___.
zoonoses
Parasitism
One (parasite) benefits; one is harmed (host)
Symptoms
Subjective characteristics of a disease that can be felt by the patient alone.
Infection
Successful invasion of the body by a pathogenic microorganism.
Direct contact transmission
Spread of pathogens from one host to another involving body contact between hosts.
symbiosis
"to live together"
Portals of Exit
(ex nose, mouth, and urethra) allow pathogens to leave the body and are of interest in studying the spread of disease.
streptokinase
(fibrinolysin)-enzyme that degrades clots; produce by Strep. pyogenes; direct injection into blocked blood vessels to treat myocardial infarction.
systemic infection
(generalized) infection-affects the entire body, and the pathogens are widely distributed in the blood and lymph.
hyaluronidase
(the spreading factor)-enzyme that digests hyaluronic acid which is part of all-connective tissues; produced by most species of streptococcus
eg of Opportunistic Pathogens:
1. Introduction of normal flora into unusual site. E. coli is non-pathogenic in the large intestine; certain strains become pathogenic when it gets into the urethra leading to urinary tract infection 2. Immune suppression, immunocompromised Disease, malnutrition, extremes of age, chemotherapy, immunosuppresant drugs, HIV (AIDS) 3. Changes in the normal microbiota e.g.,vaginitis resulting from a broad spectrum antibiotic killing resident Lactobacillus
criteria Koch's Postulates
1. The same pathogen must be found in all organisms suffering from the disease but not necessarily in healthy organisms 2. The pathogen must be isolated from a diseased organism and grown in pure culture 3. The cultured pathogen must cause the disease when introduced into a healthy organism. 4. microorganism must be re-isolated from the inoculated, diseased host and identified as being identical to the original specific pathogen
Diseases can be descibed as 1. acute 2. subacute 3. chronic 4. latent
1. disease develops rapidly but lasts only a short time (common cold) 2. have durations and severities that lie somewhere between acute and chronic. (endocarditis, a disease of heart valves) 3. develop slowly and are continual or recurrent. (mononucleosis, hep C, TB, leprosy) 4. a pathogen remains inactive for a long period of time before becoming active. (Herpes)
1. Vectors 2. Biological vectors 3. Mechanical vectors
1. transmit pathogens between hosts. 2. animals (usually biting arthropods) serve as both host and vector pathogens. 3. not hosts to the pathogens they carry.
classification of disease outbreaks as 1. endemic 2. spiradic 3. epidemic 4. pandemic
1. usually present 2. occasional 3. more cases than usual 4. epidemic or more than one continent
Pathogen
Any parasite that causes disease
Nosocomial disease
A disease acquired in a healthcare facility.
Contagious disease:
A disease that is easily spread from one host to another A sub-category of communicable disease; Ex: chickenpox
Noncommunicable disease:
A disease that is not transmitted from one host to another. many normal flora that are opportunistic pathogens Examples: tooth decay, urinary tract infections
Communicable disease:
A disease that is spread from one host to another. Examples: tuberculosis, influenza, herpes, HIV
Epidemic
A disease that occurs at a greater than normal frequency for a given area or population
Endemic
A disease that occurs in a relatively stable frequency within a given area or population.
Sporadic
A disease that occurs in only a few scattered cases within a given area or population during a given period of time.
Syndrome
A group of symptoms, signs, and diseases that collectively characterizes a particular abnormal condition.
Virulence
A measure of pathogenicity.
Pathogenicity
A microorganism's ability to cause disease.
pathogen
A parasite that causes disease; disease causing microbe
Opportunistic Pathogens
A pathogen that doesn't affect healthy host, but do in weakened immune states or abnormal body conditions
Biofilm
A slimy community of microbes growing on a surface, example: dental plaque
Morbidity
AKA disease- a condition sufficiently adverse enough to interfere with normal functioning of the body.
Pathogenicity
Ability of a microorganism to cause disease; In order for disease to result from an infection, the pathogen must evade the host's defense system
Skin (portal of entry)
Access can be gained via (normal) openings such as hair follicles and sweat glands. Other openings such as abrasions, cuts, bites, scrapes, and surgeries may also open the body to infection.
The Movement of Microbes into Hosts:
Adhesion
Virulence factors include:
Adhesion factors, Biofilms, Antiphagocytic factors, Extracellular enzymes, Toxins
Nosocomial infection
An infection acquired in a healthcare facility.
Vectors
Animals that carry pathogens from one host to another, Most notably: arthropods, especially fleas, ticks, and mosquitoes
Disease
Any adverse internal condition severe enough to interfere with normal body functioning.
Biological vector
Biting arthropod or other biting animal that transmits pathogens and serves as a host for the multiplication of the pathogen during some stage of the pathogen's life cycle.
Hyaluronidase
Breaks down hyaluronic acid, The "glue" that holds cells together, Also known as the "Spreading Factor": helps bacteria spread thru a tissue, Sometimes mixed with a drug to help spread the drug thru a body tissue, Released by sperm cells to help penetrate egg
Compromised Host 2 principal conditions compromise the host:
Broken skin/Mucous Membranes: Intact skin and mucous membranes provide a physical barrier against pathogen/ first line of defense: Burns, surgical wounds, trauma, invasive procedures, urinary catheters, etc. all breakdown this barrier and/or produce a pathway into host Suppressed immune system: Adversely affect the actions of white blood cells and antibody production
Coagulase
Cause blood to clot "hiding" the bacteria; converts fibrinogen to fibrin, which forms blood clots; The fibrin coated bacteria is thus protected from phagocytosis from WBC's. e.g., Staphylococcus aureus, boils, abscesses
Illustrations of the different terms for the occurrence of disease-overview
Centers for Disease Control and Prevention (CDC) Main source epidemiological information in the U.S. Issues Morbidity and Mortality Weekly Report; Available at website: www.cdc.gov Contains information on the morbidity and mortality of nationally notifiable diseases
Where are normal flora found?
Certain regions tend to see more, some areas none; Distribution/Composition determined by: Nutrients (secretions, body fluids, food in GI tract), Physical and Chemical factors (pH, oxygen, salt), Mechanical factors (chewing, flow of mucus and urine, muscular movements of throat, stomach, etc.) Normal flora vary, affected by: Age, diet, health, emotional stability, stress, climate, occupation
Toxins
Chemicals that either harm or trigger host immune responses that cause damage.
Toxins
Chemicals that harm tissues or trigger host immune responses that cause damage (aka poisons); Toxins are the primary factor contributing to a bacteria's ability to cause disease; There are 220 known bacterial toxins
Bacterial capsules
Composed of chemicals not recognized as foreign, Slippery (hard to attach to) Example: Streptococcus pneumoniae can only cause disease if it has a capsule. Unencapsulated cells are quickly engulfed and killed by body defenses
3 modes of infectious disease transmission
Contact transmission, vehicle transmission, and vector transmission.
Three groups of transmission
Contact transmission; Direct, indirect, or droplet Vehicle transmission; Airborne, waterborne, or foodborne Vector transmission; Biological or mechanical
Exposure to Microbes:
Contamination vs. Infection
Exotoxins 3 main types:
Cytotoxins: kills host cells in general Neurotoxins: interfere with nerve cells Enterotoxins: affects cells lining the GI tract
Virulence
Degree of pathogenicity; The relative ability of a pathogen to invade a host and cause disease
contamination
state where microbes are present.
IgA Proteases
Destroys IgA antibodies; Main antibody found in mucosal secretions, such as tears, saliva, vaginal secretions, respiratory secretions, digestion secretions; e.g, N. gonorrhoeae and N. meningitidis
Acquisition of normal flora
Development in womb is essentially axenic Microbe free; During the birthing process, our first normal flora acquired; Intestinal bacteria acquired from first meals; Skin flora acquired from contact with parents and others
Kinases
Digest blood cots by breaking down fibrin, allowing bacteria to spread. e.g., streptokinase produced by Streptococcus pyogenes, e.g, staphylokinase produced by Staphylococcus aureus
Chain of Transmission
Direct contact between hospital staff and patients AND between patients themselves; Hospitals create unsavory environment for multiple microbe transmissions in immuno-suppressed patients Still home efficient than home treatment Indirect contact transmission through fomites and ventilation systems; Fomites include bedding, urinary catheters, IV catheters, needles, etc.
various routes zoonoses r acquired
Direct contact with animal or its waste; Eating animals; Bloodsucking arthropods Over 150 zoonose have been identified Rabies, Lyme disease, Malaria
Severity and Longevity of Disease Chronic
Disease develops slowly and bodies reaction may be less severe; however, it tends to last a long time. Tuberculosis, hepatitis B
Zoonoses
Diseases that are naturally spread from usual animal hosts to humans.
Clostridium perfringens
Gas Gangrene uses collagenase to spread thru muscle tissue
Common sexually transmitted disease
Gonorrhea; Neisseria gonorrhoeae; Syphilis; Treponema pallidum; Chlamydia; Chlamydia trachomatis; HIV; Herpes; Genital Warts
Both Organisms Benefit
E. coli of the large intestine synthesize vitamin K and some B vitamins (We use vitamins to assist with clotting and as co-enzymes E. coli get a free meal in our gut. We provide the bacteria with food)
urinary tract catheterization
E. coli responsible for nosocomial infection
Portal of entry
Entrance site of pathogenic microorganisms, including the skin, mucous membranes, and placenta.
Extracellular enzymes
Enzymes that enable pathogens to dissolve structural chemicals in the body and maintain an infection, invade further, and avoid body defenses. Example: Keratinase, an enzyme produced by the fungi that cause ringworm, enzymatically digests keratin - the main component of skin, hair, and nails.
Virulence factors
Enzymes, toxins, and other factors that affect the relative ability of a pathogen to infect and cause disease.
Types of nosocomial infections
Exogenous: Pathogen acquired from the health care environment Endogenous: Pathogen arises from normal flora (microbiota) due to factors within the health care setting, such as compromised immune system; Opportunistic pathogens Iatrogenic: Results from modern medical procedures, such as catheterization
Collagenase
Exotoxin that breaks down collagen, which is the chief structural protein in connective tissue
Two types of toxins
Exotoxins; Endotoxins
The Role of Adhesion in Infection
Once microbe gain access to the body, they need to adhere to cells in order to successfully establish colonies within host
Decline
Final stage of disease; The body gradually returns to normal as the patient's immune response and/or medical treatment vanquish the pathogens. The immune response and its products peak during this stage.
Incubation period
First stage of disease; the time between infection and occurrence of the first symptoms or signs of disease. Length depends on the virulence of the infective agent, the infective dose, the state of health of the host's immune system, the nature of the pathogen and its reproduction time, and the site of infection.
Which of the following statements is the best definition of a pandemic disease?
It is an epidemic that occurs on more than once continent at the same time.
Endotoxin is the part of the cell wall of a Gram-negative bacterium know as ___.
Lipid A
Reservoirs of infection
Living and nonliving continous sources of infectious disease.
Reservoir of infection
Living or nonliving continuous source of infectious disease
Conjuctiva
Membrane that covers the eyeballs and eyelids; Many viruses are introduced into the conjuctiva by contaminated fingers and then washed into the nasal cavity with tests; This is a typical route for the flu virus and common cold
Gastrointestinal (GI) Tract
Microbes gain entrance thru contaminated food and water or fingers and hands; poor personal hygiene. Most microbes that enter the G.I. Tract are destroyed by HCL & enzymes of stomach or bile & enzymes of small intestine. Those that survive can cause disease; eliminated thru feces, and transmitted to other hosts
Subcutaneous (Parenteral) Route
Microorganisms are deposited into the tissues below the skin or mucus membranes. Punctures; Injections; Bites; Scratches; Surgery; Splitting of skin due to swelling or dryness
Opportunistic pathogens
Microorganisms that cause disease when the immune system is suppressed, when microbial antagonism is reduced, or when introduced into an abnormal area of the body.
Respiratory Tract
Most frequently traveled portal of entry; Microbes inhaled into mouth or nose in droplets of moisture or dust particles; Line with mucous membranes, which provide a warm, moist, hospitable environment
Human Carriers
Most important reservoir; it Can be with noticeable symptoms/signs or carriers
Microbes live in Symbiotic relationships.. what are the types?
Mutualism (both members benefit) Parasitism (parasite benefits while the host is harmed) Commensalism (One member benefits while the other is relatively unaffected)
Microbial antagonism
Normal condition in which established microbiota use up available nutrients and space, reducing the ability of arriving pathogens to colonize.
track occurrence of diseases using two measures: Incidence & Prevalence
Number of new cases of a disease in a given area during a given period of time Number of total cases of a disease in a given area during a given period of time Example: The incidence of HIV in the US in 2004 was 40,000; prevalence was 900,000. This means that 40,000 people became infected with HIV that year. This means that in 2004, 900,000 in the U.S. had the HIV virus
Commensalism
One benefits, one is unaffected; Many microbes that inhabit eyes, ears, and genitals; many of the microbes in the intestine. Bacteria benefit: nutrients from secretions and dead cells; protection/place to live Host unaffected: no apparent advantage to us Competitive exclusion may play a role (keeping other harmful microbes away)
Normal flora (aka normal microbiota)
Organisms that colonize the body's surfaces without normally causing disease 10x more bacterial cells than body cells Each square cm of skin contains about 3 million bacteria! Your intestines contain 400-1000 kinds of bacteria!
Adhesion
Pathogens attach to cells via a variety of structures or attachment proteins called adhesion factors. Some bacteria and viruses lose the ability to make a adhesion factors called adhesions and thereby become avirulent.
Resident microbiota
Remain a part of the normal microbiota of a person throughout life. Found on the skin, mucous membrane (of the digestive tract), upper respiratory tract, and the distal portions of the urethra and vagina. Considered commensal - feed on extracellular wastes and dead cells without causing harm to the host.
Transient microbiota
Remain in the body for only a few hours, days, or months before disappearing. Cannot persist in the host due to the competition between indigenous microbiota, elimination by the body's defenses, or chemical and physical changes that dislodge them.
Contact transmission, Direct:
Requires contact between infected and susceptible host. "person to person" (touching, kissing, sex) warts, herpes, gonorrhea. Some zoonoses spread by toucing, scratches, bites, etc. Ringworm, rabies
5 major pathways
Respiratory Tract; Gastrointestinal tract Genitourinary tract; Skin Subcutaneous or intramuscular; (Parenteral) route
surgical wounds
S. aureus responsible for nosocomial infection
Common diseases contracted via the G.I. Tract
Salmonellosis, Salmonella sp., Shigellosis, Shigella sp., Cholera, Vibrio cholorea, Ulcers, Helicobacter pylori, Botulism, Clostridium botulinum
Prodromal period
Second stage of disease; A short time of generalized, mild symptoms that precedes illness. Not all infectious agents have this stage.
Extracellular enzymes
Secreted by the pathogen, Dissolve structural chemicals in the body, Help pathogen maintain infection, invade, and avoid body defenses. Examples: Coagulases, Kinases, Collagenase, Hyaluronidase, IgA Proteases
Portals of exit
Sites through which microorganisms leave the body; examples: nose, mouth, urethra
Portals of Entry
Sites through which pathogens enter the body
Reservoirs of infection
Sites where pathogens are maintained as a source of infection, Most pathogens cannot survive for long outside their host
Indirect contact transmission
Spread of pathogens from one host to another via inanimate objects called fomites; examples: needles, toothbrushes, paper tissues, money, medical equipment, and drinking glasses.
Nonliving Reservoirs
Soil, water, and food can be reservoirs of infection Often due to contamination by feces or urine Clostridium botulinum enters soil from manure Salmonella typhi (typhoid fever) enters water from feces
Nonliving reservoir of infection
Soil, water, food, or inanimate object that is a continuous source of infection
Antiphagocytic chemicals
Some bacteria release chemicals that protect themselves from digestion after being enveloped by phagocytes; Some bacteria make chemicals that help resist a cell becoming phagocytized in the first place; Waxy cell wall of Mycobacterium tuberculosis resists phagocytosis; Some bacteria can release leukocidins, which actually destroy white blood cells
Exceptions to Koch's Postulates
Some microbes cannot be grown on artificial media; e.g., Treponema pallidum (syphillis) and Mycobaterium leprea (leprosy) Different microbes can cause same symptoms (hence same disease); Nephritis (kidneys), pneumonia, meningitis Same pathogen can cause multiple diseases depending on location and host; Mycobacterium tuberculosis can cause diseases of lungs, skin, bones, etc. Ethical considerations; You can't just go around injecting people and animals with disease. For example, humans are the only host for HIV...so Koch's postulates have never been applies to prove that HIV causes AIDS
frequency of Disease
Sporadic disease: disease that occurs occasionally in a population; usually a few scattered cases; e.g., typhoid fever Endemic disease: disease that normally occurs continuously in a population at predictable incidence rates e.g., common cold, malaria (in some parts of the world) Epidemic disease: disease occurs at a greater frequency than what is usual within a population; Note: within a localized area Pandemic disease: worldwide epidemic. AIDS; H1N1 (swine) flu of 2009
Contact transmission; inDirect:
Spread by fomites. For example: HIV and heptatitis B spread thru contaminated needles
Foodborne transmission
Spread of pathogenic microorganisms in or on foods that are poorly processed, undercooked, or improperly refrigerated.
Bodily fluid transmission
Spread of pathogenic microorganisms via blood, urine, saliva, or other bodily fluids.
Waterborne transmission
Spread of pathogenic microorganisms via water.
respiratory tract
Streptococcus responsible for nosocomial infection
Normal microbiota
The group of microbes that normally inhabit the surfaces of the body without causing disease, also known as indigenous microbiota.
An animal was infected with a virus. A mosquito bit the animal, was contaminated with the virus, and proceeded to bite and infect a person. which was the vector?
The mosquito
Incidence
The number of new cases of a disease in a given area or population during a given period of time; # of new cases/ # of people at risk.
Pandemic
The occurrence of an epidemic on more than one continent simultaneously.
Contamination
The presence of microbes in/on the body thru several portals of entry; Some microbial contaminants remain residents of the body and become part of normal flora, while others remain only a short amount of time as transient flora; Others...cause infection
Contamination
The presence of microorganisms in or on the body or other site.
Contact transmission
The spread of pathogens from one host to another by direct contact, indirect contact, or respiratory droplets.
Waterborne:
spread thru water; Especially for many GI diseases Fecal-oral route is a major source of diseases worldwide
high risk procedures for nosocomial infections
Urinary tract catheterization, surgical wounds, and respiratory tract.
when pathogenic bacteria win and disease results:
Vaginitis: results when normal flora population is decreased and pH reaches neutrality; promotes excessive growth of Candida albicans (yeast) Clostridium difficile normally limited by normal flora of intestine; antibiotics can decrease normal flora allowing C. difficile to flourish and cause GI infections (diarrhea or worse!)
Indirect Contact Transmission
When pathogens are transmitted via inanimate objects (fomites)
nutritional
result from lack of some essential nutrients in diet
Fecal-oral Infection
result from sewage contaminated drinking water or from ingesting fecal contaminants.
Disease
results if the invading pathogen alters normal body functions (loss of homeostasis)
Exotoxins
secreted by pathogens into their environment
Analytical epidemiology
seeks to determine the probable cause of a disease.
Portals of entry of pathogens into the body
skin, mucous membranes, the placenta, and the parenteral route, by which microbes are directly deposited into deeper tissues.
exotoxins
soluble protein substances produced (mainly) inside Gram-positive bacteria during normal metabolic processes, which are then secreted into host tissues.
Biofilm
some bacteria interact to produce a sticky web of cells and polysaccharides that adheres to a surface.
opportunists
some of the normal flora, can under special circumstances, produce disease are called
Airborne:
spread of pathogens farther than 1 meter to the respiratory mucous membranes of a new host via an aerosol (cloud of small droplets and particles suspended in the air) Generated from coughing, sneezing, generated from air conditioners, sweeping, changing bed sheets, etc.
Bodily Fluid Transmission
spread of pathogens via blood, urine, saliva, or other fluids