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

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