Chapter 14: Infection, Infectious Diseases, and Epidemiology

Question 1

What are Symbiotic Relationships and what are the three types?

Answer 1

Symbiosis- to live together

Types of symbiosis:

Mutualism (both members benefit)

Commensalism (one member benefits where the other is unaffected)

Parasitism- one member negatively affects the other Any parasite that causes disease is called a pathogen

Question 2

What are some examples of Symbiosis?

Answer 2

Mutualism- bacteria in the human colon

Commensalism- staphylococcus on skin

Parasitism- M. tuberculosis in lung

Question 3

What are the terms used to describe normal microbiota?

Answer 3

Also termed normal flora and indigenous microbiota

Organisms that colonize the body’s surfaces without normally causing disease

Two types:

Resident microbiota (always present, part of normal microbiota throughout life, mostly commensal)

Transient microbiota (temporary, cannot persist due to competition, elimination by body’s defense cells, chemical/physical changes in body)

Question 4

How is normal microbiota acquired?

Answer 4

Development in womb free of microorganisms (axenic)

Microbiota begin to develop during birthing process

Much of one’s resident microbiota established during the first months of life

Question 5

What is an opportunistic pathogen?

Answer 5

Normal microbiota that cause disease under certain circumstances

Question 6

How does a bacteria become an opportunistic pathogen?

Answer 6

Introduction of normal microbiota into unusual site in body Immune suppression

Changes in normal microbiota

Changes in relative abundance may allow opportunists to thrive and cause disease

Question 7

What is a reservoir of infection and what are the three types?

Answer 7

Sites where pathogens are maintained as a source of infection

3 Types: Animal Reservoir Human Carriers Nonliving Reservoir

Question 8

What are animal reservoirs? What are zoonoses?

Answer 8

Zoonoses- diseases naturally spread from animal host to humans (anthrax, plague, rabies)

Acquire zoonoses through various routes Direct contact, eating animals, bloodsucking arthropods

Humans are usually dead-end host to zoonotic pathogens

Question 9

What are human carriers and what are the characteristics of a human carrier?

Answer 9

Infected individuals who are asymptomatic but infect others

Some individuals eventually develop illness with others never get sick

Healthy carriers may have defensive systems that protect them

Question 10

What are and types of nonliving reservoirs?

Answer 10

Soil, water, and food can be reservoirs of infection

Presence of microorganisms often due to contamination by feces or urine

Meat, milk, and vegetables also harbor pathogens

Question 11

Define Contamination

Answer 11

The mere presence of microbes in or on the body

Question 12

Define Infection

Answer 12

When organisms evades body’s external defenses, multiplies, and becomes established in the body

Question 13

What are the portals of entry?

Answer 13

Sites through which pathogens enter the body

4 Major Routes:

Skin Mucous Membranes Placenta Parental Route

Question 14

Skin

Answer 14

Outer layer of dead skin cells acts as a carrier to pathogens

Some pathogens can enter through openings or cuts

Others enter by burrowing into or digesting outer layers of skin

Question 15

Mucous Membranes

Answer 15

Line the body cavities that are open to the environment

Provide a moist, warm environment that is hospitable to pathogens

Respiratory tract is the most common site of entry (entry through nose, mouth, or eyes)

Gastrointestinal tract may also be a route of entry (must be able to survive acidic pH of stomach)

Question 16

Placenta

Answer 16

Developing embryo forms an organ called a placenta through which it obtains nutrients from the mother

Typically forms effective barrier to pathogens

Pathogens may be able to cross the placenta and infect the fetus, cause spontaneous abortion, birth defects, and premature birth

E.g. Listeria, Treponema pallidum, Toxoplasma gondii

Occurs in about 2% of pregnancies

Question 17

Parental Route

Answer 17

Not a true portal of entry

Means by which portal of entry can be circumvented

Pathogens deposited directly into tissues beneath the skin or mucous membranes

Question 18

What is the role of adhesion in infection?

Answer 18

Adhesion- process by which microorganisms attach themselves to cells

Required to successfully establish colonies within the host

Use adhesion factors- Specialized structures (Adhesion disks, hooks, suckers)

Ligands: Adhesins in bacteria or attachment proteins in viruses

Question 19

Ligands: Adhesins and Attachment Proteins

Answer 19

Attachment proteins help in adhesion

Found on viruses and many bacteria

Viral or bacterial ligand bind to host cell receptors, interaction can determine host cell specificity

Changing/blocking a ligand or its receptor can prevent infection Inability to make attachment proteins or adhesins renders microorganisms avirulent

Some bacterial pathogens attach to each other to form a biofilm

Question 20

The Nature of Infectious Disease

Answer 20

Infection and disease are not the same thing

Infection- invasion of the host by a pathogen

Disease results if the invading pathogen alters normal body function, also referred to as morbidity and is any change in a state of health

Question 21

What is the difference between signs and symptoms?

Answer 21

Symptoms- subjective characteristics of the disease felt only by the patient

Signs- objective manifestations of disease observed by others

Syndrome- group of symptoms and signs that characterize an abnormal condition

Asymptomatic, or subclinical infections, lack symptoms but may still have signs of infection

Question 22

What is Etiology?

Answer 22

Etiology is the study of the cause of disease

Pasteur- Germ Theory of Disease (disease caused by infections of pathogenic microorganisms)

Robert Koch- developed a set of postulates to a prove that a particular pathogen causes a particular disease

Question 23

Koch’s Postulates

Answer 23

4 Postulates to follow:

1. The causative agent must be found in every case of the disease
2. The agent must be isoalted and grown outside of the host
3. The agent must be reintroduced into a healthy host and a change in health of the host must occur
4. The causative agent must be found to be causing the changes of healthy in the experimental host

Question 24

What are the exceptions to Koch’s Postulates?

Answer 24

Some pathogens cannot be cultured in the lab

Diseases may be caused by a combination fo pathogens and other cofactors

Ethical considerations prevent applying Koch’s postulates (require introduction of possible pathogen into a human)

Difficult to establish a single cause of disease (meningities, hepatitis, etc.)

Pathogens may be ignored as potential causes of disease

Question 25

Pathogenicity vs. Virulence

Answer 25

Pathogenicity- the ability to cause disease

Virulence- degree of pathogenicity

Virulence factors contribue to virulence, they include:

Enzymes, toxins, adhesion factors, biofilms, and antiphagocytic factors

Question 26

What are extracellular enzymes?

Answer 26

Enzymes secreted by the pathogen that dissolve structural chemicals in the body

Help the pathogen maintain infection, invade, and avoid body defenses

Examples:

Hyaluronidase and Collagenase- break down hyaluronic acid (glue that holds cells together) and collagen cells, help to invade deeper into cells

Coagulase and Kinase- helps to form blood clots and kinase helps to break them

Question 27

What are the effects of toxins?

Answer 27

Chemicals that harm tissues or trigger host immunity responses that cause damage

Toxemia- refers to toxins in the blood stream that are carried beyond the site of infection

Two types of toxins:

Exotoxins- secreted from living cells, cytotoxins, neurotoxins, and enterotoxins

Endotoxins- portion of outer cell wall membrane released upon cell death (Lipid A) of gram negatvie bacteria

Treated with antitoxins

Question 28

What are the effects of antiphagocytic factors?

Answer 28

Factors that precent phagocytosis by the host’s phagocytosis

Bacterial capsule- composed of chemicals not recognized as foreign, slippery, difficult for phagocytes to engulf bacteria

Antiphagocytic chemicals- prevent fusion of lysosome and phagocytic vesicles

Leukocidins directly destroy phagocytic white blood cells

Question 29

What are the five stages of infectious disease?

Answer 29

1. Incubation period- sign between the infection and first signs of symptoms
2. Prodromal period- a short time of generlaized, mild symptoms that precede illness
3. Disease- immune system at lowest point, most severe stage of illness
4. Decline- immune system and body at peak, body gradually returns to normal
5. Convalescence- repair of tissues, recovery

Question 30

What are the portals of exit for a pathogen?

Answer 30

Portal of exit is where a pathogen leaves the body

Most portals of exit are the same as the portals of entry (mucous membranes, skin)

Pathogens often leave hosts in materials the body secretes or excretes including: tears, nose secretions, saliva, sputum, milk, bood, urine

Question 31

What is tranmission and what are the three types of transmission?

Answer 31

Transmission is the movement of a pathogen from a reservoir or a portal of exit to another host’s portal of entry

3 Types:

Contact transmission- spread person to person (direct, indirect, or droplet)

Vehicle transmission- spread to a large area (airborne, waterborne, or foodborne)

Vector transmission- Biological (Anopheles) or mechanical (Musca) (animals that transmit diseases from one host to another)

Question 32

What are the ways in which diseases may be classified?

Answer 32

The body system they affect

Taxonomic categories

Their longevity and severity

How they are spread to their host

The effects they have on populations

Question 33

What are the terms used to classify a disease by its longevity and severity?

Answer 33

Acute disease- rapid onset, lasts a short time

Chronic- slow onset, lasts an extended period of time

Subacute disease- in between chronic and acute

Latent disease- pathogen remains inactive for a long time before becoming active

Communicable- comes from another infected host

Contagious- easily transmissible between hosts

Question 34

What is epidemiology? What are the terms used to describe the frequnecy of disease?

Answer 34

Epidemiology is the study of the spread of a disease throguh a population

Frequency of a disease is measured by:

Incidence- number of new cases that have developed in a given area during a certain time period

Prevalence- numebr of total cases of disease in a given area during a certain time period

Occurrence also evaluated in terms of frequency and geographic distribution

Question 35

What are the differences between endemic, sporadic, epidemic, and pandemic?

Answer 35

Endemic- normal occurrence of a disease in a given area

Sporadic- few given cases of a disease

Epidemic- frequency of a given disease in ana area rises

Pandemic- frequency of a disease is higher in several continents

Question 36

What are the types of nosocomial infections?

Answer 36

Three types of nosocomial infections:

Exogenus- pathogen acquire from the health care environment

Endogenous- pathogen arises from normal microbiotia due to the facotrs within the health care setting (opportunistic pathogens)

Iatrogenic- results from modern medical procedures (heart valves, joints, catheters, etc)

Question 37

How do you control nosocomial infections?

Answer 37

Precautions designed to reduce factors that result in disease

Hand washing is the most effective way to reduce nosocomial infections

Question 38

What public health agencies are involved with epidemiology?

Answer 38

Agencies at the local, state, national, and global level share information concerning disease

The United States Public Health Service, World Health Organization (WHO)

Public health agencies work to limit disease transmission- monitor water and food safety

Public health agencies campaign to educate the public on healthful choices to limit disease