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156 terms

Microbiology: Unit 4, Part 1: Epidemiology

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Definition: The cause the disease
Etiology
Definition: Manner in which the disease develops
Pathogenesis
Definition: Structural and functional changes
Results of the disease
Definition: Penetration of the body's non-specific defense mechanisms
Infection
Definition: Growth of organisms within or on the body's surface
Colonization
Definition: A negative change in the state of health of an individual
Disease
What is the first stage of a microbial infection?
Colonization
Where do pathogens usually colonize?
In host tissues that aren't in contact with the external environment
Definition: Organisms that regularly inhabit the human body; may or may not be capable of causing disease
Normal Flora
Definition: Organisms that only occasionally come into contact with the human body; the most frequent cause of disease
Transient Flora
Types of symbiosis between bacteria and humans
Mutualism, commensalism, parasitism
Definition: Both organisms and bacteria benefit from the relationship
Mutualism
Definition: One organism benefits, but the other remains neutral
Commensalism
Definition: One member benefits, but the other is harmed
Parasitism
Definition: An organism that must exist in a parasitic relationship
Obligate parasite
Definition: An organism that usually does not require a parasitic relationship, but will establish one when the opportunity arises
Facultative parasite
Main categories of disease
Infectious, nutritional deficiency, congenital, inherited, metabolic, degenerative, neoplastic, immunologic
Definition: A condition that makes the body more susceptible to a disease or alters the course of the disease
Predisposing Factors
List the predisposing factors
Gender, genetic background, climate, age, nutritional habits, unhealthy environment
Definition: A continual source of infection
Reservoir of infection
Definition: Includes individuals who currently have the disease or are carriers from previous infections
Human reservoirs
Definition: Diseases carried by animals, but can be transmitted to humans called "zoonoses"
Animal reservoirs
Type of disease transmission: directly from one host to another through intercourse, handshaking, kissing, etc OR some time of close association between the hosts such as droplet infection from mouth or nose
Direct contact
Diseases transmitted by direct contact?
Tuberculosis, measles, diphtheria, common cold, smallpox
Most infectious organisms cannot survive ________ of the body.
outside
Definition: Transmission of pathogens by food, water, and contaminated objects
Indirect contact
Definition: Non living objects that spread infection
Fomites
Most diseases spread by indirect contact enter the body by the _____, and can survive ________ the body for extended periods of time.
Mouth, outside
Definition: A very important group of disease vectors that carry pathogens from one host to another. Two general methods are used.
Arthropod vectors
What are the two general methods used by arthropod vectors?
Mechanical and biological
Type of vector method: Carrying organism on body parts, especially feet that contaminate food
Mechanical
Type of vector method: Insect bites infected person and ingests blood. Typically, the organism multiplies, the is spread when vector bites an uninfected person
Biological
Any disease spread from one host to another by any method
Communicable diseases
A disease caused by members of the normal flora or by organisms introduced directly into the body
Noncommunicable disease
A disease easily spread from one host to another
Contagious disease
The fraction of a population that contracts the disease during a particular length of time
Incidence
The fraction of the population having the disease at any given time
Prevalence
A disease that develops rapidly, but lasts only a short period of time
Acute disease
A disease that develops more slowly, but is continuous or reoccurs for long periods of time
Chronic disease
A disease that occurs occasionally
Sporadic disease
A disease that is constantly present within a population
Endemic disease
A disease acquired by an unusually large number of people in a given area with a short period of time
Epidemic disease
Epidemic usually produced from spread by contaminated source
Common-source epidemic
Epidemic where disease results from spread by individuals
Person-to-person epidemic
World wide epidemic
Pandemic
Type of Infection:Pathogens limited to a relatively small area of the body
Local infection
Type of Infection: Pathogens or their products spread throughout the body
Systemic Infection
Type of Infection: Presence of bacteria in the blood
Bacteremia
Type of Infection: Bacteria that actually multiply in the blood
Septicemia
Type of Infection: An acute infection that causes an initial illness
Primary infection
Type of Infection: Caused by an opportunistic pathogen after a primary infection has weakened the immune system
Secondary infection
Type of Infection: Infection that does not cause any signs or symptoms
Inapparent orsubclinical infection
Symptoms
Any negative change that is not visible or measurable (such as pain, nausea, weakness, etc)
Signs
Any negative change that is visible or measurable (such as diarrhea, fever, inflammation, edema, etc)
The science that deals with when and where the disease occurred and how it is transmitted
Epidemiology
Epi means
Upon
Demos means
People
Logos means
The study of
The main premise of epidemiology
Disease does not occur at random, but rather in patterns that reflect the operation of underlying factors.
The primary goal of epidemiology
To measure the relationships between "exposures" and health outcomes which may provide a basis for public health initiatives and policies
The study of the distribution and determinants of disease frequency in human populations
Epidemiology
The study of the distribution and determinants of health-related states or events in specific populations, and the application of this study is to control health problems
Epidemiology
Epidemiology: Methodology steps
Defining a health problem, determine the extent of diseases in the community, study the natural history of the disease, identify associations and potential etiology (causes) of a disease and risk factors for disease, and evaluate new preventative and therapeutic measures and new modes of health care delivery
Epidemiology: Steps to the science of public health
Identify risk factors associated with the problem, develop and test community level interventions to control or prevent the causes of the problem, Implement interventions to improve the health of the population, monitor those interventions to assess their effectiveness
Conditions for a disease outbreak
Agent and susceptible hosts are present in sufficient number and the agent can be effectively conveyed from a source to susceptible hosts
Causes of disease outbreaks
1. Increase in amount or virulence of agent
2. Recent introduction of the agent into a new setting
3. Enhanced mode of transmission, exposing more susceptible individuals
4. Factors that increase host exposure or involve introduction through new portals of entry
The time interval from infection to development of infectious period
Latent period
The time during which the host can infect another host
Infectious period
The time from infection to development of symptomatic disease
Incubation period
The period in which signs and symptoms of the disease are present
Symptomatic period
Which portal of entry: Easiest and most frequently traveled route; inhalation of moisture droplets and other air-borne particles
Respiratory tract
Portal of entry: Very common portal of entry; from food, drink, and fingers
Gastrointestinal Tract
Portal of entry: Most microbes cannot penetrate this when it is unbroken. Infection through hair follicles and sweat glands. Infection through mucous membranes is much easier.
Skin and mucous membranes
How can infection particles penetrate the skin?
Hair follicles and sweat glands
Portal of entry: Deposited directly under the skin and mucous membranes by injury (bites, cuts, surgery, injection)
Parenteral route
What is the most dangerous portal of entry and why?
The parenteral route because it provides direct input into the bloodstream
Which enzymes break down blood clots?
Streptokinase and staphylokinase
All species of salmonella are ________ (pathogenic/nonpathogenic).
Pathogenic
What is the only way to penetrate unbroken skin?
Mechanical penetration (by enzymes)
Pathogenicity
The ability of a pathogenic organism to cause disease in a host
Virulence
The degree of pathogenicity; how potentially successful a pathogen is
Expressed virulence
LD₅₀ and ID₅₀
LD₅₀
A dose that will kill 50% of inoculated hosts within a given time (deaths)
ID₅₀
The dose required to produce demonstratable infection in 50% of hosts (infections)
The ability to invade tissues
Invasiveness
Pathogenic Properties of bacteria
Invasiveness, mechanisms of colonization (adherence and initial multiplication), ability to bypass or overcome host defense mechanisms, and the production of extra cellular substances which facilitate invasion
Pathogenic bacteria cause disease by two basic functions: _______ & __________
Invasiveness and Physiological processes by toxins
Colonies due to invasiveness are evidence of
The ability to establish residence in host and cause structural damage through metabolic activities
Effects of invasiveness
Significant damage in immediate vicinity of infection
Invasiveness and tissue damage is facilitated by
glycocalyx, toxins, and components of the cell wall
Function in invasiveness: Capsules
Resist phagocytosis by white blood cells
Function in invasiveness: Components of cell wall
M-protein is a heat-resistant and acid-resistant protein, A-protein contributes antiphygocytotic abilities
Enzymes that contribute to invasiveness
Leukocidins, Hemolysins, and Coagulase
Function of Leukocidins
Destroy pathogens (one of the keys to specific response)
Functions of Hemolysins
Cause lysis of red blood cells (very dangerous)
Function of Coagulases
Coagulate fibrinogens in blood to form clot around bacteria to help prevent phagocytosis (not good in healthy cells)
A slimy layer external to the cell wall; will greatly decrease the ability of macrophages to engulf the bacterium
Glycocalyx
What does a glycocalyx provide?
Protection for the bacterium
What does the glycocalyx prevent?
Attachment of receptor sites
Main categories of glycocalyxes
Capsule (small/organized) and Slime layer (loose, unorganized)
What does the "physiological processes by toxins" refer to?
Toxins transported by blood and lymph that can cause damage far from the site of infection
True of false: Toxins only cause damage at the site of infection
FALSE. Toxins can cause damage far from the site of infection
To be affected by toxins, do you have to consume the bacteria?
No, just the toxins
Metabolic by-products or structural components that happen to have a negative impact on other organisms. Not produced intentionally for the purpose of damaging other cells
Toxins
What is the difference between toxins and venoms?
Toxins are by-products that are not created to harm other cells (excretion); Venoms are intentionally created for damaging and killing (secretion)
Toxins that are a structural part in the cell wall of gram negative bacteria. The bacterium must be consumed to be affected by the toxin. All produce same signs and symptoms (fever, weakness, generalized aches, possibly shocka and death, etc)
Endotoxins
Two key characteristics about Endotoxins
Only gram negative and bacterium must be consumed in order to cause harm
True or false: Bacterium must be consumed and broken down for endotoxins to cause signs and symptoms
True
Toxins that are excreted by mostly gram positive bacteria into the environment. You do not have to inject the bacterium to ingest the toxin.
Exotoxins
Two key characteristics about exotoxins
Mostly gram positive and the bacterium does not have to be ingested in order to ingest the toxin
Two types of Exotoxins
Entertoxins and Neurotoxins
Toxins that affect the gastrointestinal system (food poisoning, etc)
Entertoxins (think of Entercocci to remember this!)
Toxins that have varying effects on the nervous system
Neurotoxins
Clostridium botulinum
Neurotoxin, most deadly toxin known to man, paralyzes muscles in skin, found in dirt and so improperly canned foods, inactivated by normal heat, most common in a home environment than an industrial environment
Superantigens are _______ and lead to _______.
An over immune response and lead to death
What do cytotoxins do?
Kill or severely damage host cells
Do exotoxins require a high concentration to cause severe damage?
No, a low concentration will cause severe damage.
Gram reaction of Endotoxins
Gram negative
Chemical nature of Endotoxins
Lippopolysaccharide
Relationship to cell of Endotoxins
Part of outer membrane
Are Endotoxins denatured by autoclaving/boiling?
No
Are endotoxins antigenic?
Yes
What is the toxicity of endotoxins?
Low
Is the lethal dose of endotoxins larger or smaller than that of endotoxins?
Considerably larger
Do endotoxins have a high or low degree of specificity?
Low
Do endotoxins have enzymatic activity?
No
No endotoxins cause fever?
Yes
Gram reaction of Exotoxins?
Gram positive
chemical nature of Exotoxins?
Protein
relationship to the cell of exotoxins?
Extracellular, diffusible
Are exotoxins denatured by boiling/autoclaving?
Usually
Are exotoxins antigenic?
Yes
Do exotoxins form toxoids?
Yes
Do endotoxins form toxoids?
No
Toxicity of exotoxins?
High
Lethal dose of exotoxins compared to endotoxins?
Small
Degree of specificity of exotoxins
High degree
Is there enzymatic activity in exotoxins?
Usually
Do exotoxins cause fever?
Occassionally
Any observable changes produced by substances coded for viruses
Cytopathic Effects of Viruses
What is extremely important in creating a plan for combating a disease?
Patterns of Disease
With a disease, you are usually not contagious until....?
Signs and symptoms occur
With a disease, you are usually contagious until.....?
Signs and symptoms cease to occur
Patterns of Disease:Time interval between the infection and the first appearance of signs or symptoms
Period of Incubation
Patterns of Disease:Time characterized by FIRST signs or symptoms (fairly short)
Prodromal Period
Patterns of Disease:Time that the disease is most severe (The time that you are noticeably sick)
Period of illness
What is significant about the Prodromal period?
It is when you first begin to infect others
What is significant about he Period of Illness?
It is the height of contagion
Patterns of Disease: Time in which there is a decrease of signs and symptoms (when you begin to feel better, but still have signs and symptoms and can still infect others)
Period of decline
Patterns of Disease: Return to predisease state (almost better, some recovery related weakness may be present, time of rapid recovery)
Period of Convalescence
Most common portals of entry AND exit
Respiratory tract and gastrointestinal tract
Which portal of exit contributes to the following diseases: Tuberculosis, whooping cough, pneumonia, meningitis, measles, mumps, and influenza
The respiratory tract
Which portal of exit contributes to the following diseases:Cholera, typhoid fever, bacillary dysentery, poliomyelitis
Gastrointestinal tract
Name 3 portals of EXIT, besides the most common 2
Urogenital tract, drainage from wounds, and insect bites
True or false: Many diseases can enter through one part of the body and affect another part
True
Dissolve fibrin and blood clots formed by body to isolate bacterial infections
Kinases