Chapter 14 — Infection, Infectious Disease, and Epidemiology

What is resident microbiota?

Microorganisms that normally colonize body surfaces and can persist there without normally causing disease.

What is transient microbiota?

Microorganisms that remain in the body for a short period but cannot persist because of competition, body defenses, or chemical and physical changes.

What are opportunistic pathogens?

Normal microbiota that cause disease under certain circumstances, such as entering a non-resident body area or affecting an immunocompromised person.

What factors contribute to a person's microbiome?

Route of birth, diet, genetics, early antibiotic treatment, lifestyle, and geographical location.

What did the microbiota transplant studies in germ-free mice demonstrate?

Mice given microbiota from obese or lean human twins took on characteristics of the donor microbiota.

What happened when mice with obese and lean microbiota were housed together on an appropriate diet?

Lean microbiota invaded mice with obese microbiota, and those mice did not develop increased adiposity; obese microbiota did not effectively colonize lean mice.

What are zoonoses?

Diseases that naturally spread from an animal host to humans.

How can zoonoses be transmitted?

Direct contact with animals or their waste, eating animals or contaminated animal products, and bites from bloodsucking arthropods.

Which animals are listed as reservoirs for common zoonoses?

Dogs, sheep, cattle, monkeys, cats, domestic animals, domestic livestock, rodents, deer, birds, reptiles, bats, skunks, foxes, and deer mice.

What are the three major portals of entry for pathogens?

Skin, mucous membranes, and placenta.

How can pathogens enter through the skin?

Through openings or cuts, or by burrowing into or digesting the outer layers of skin.

What are mucous membranes, and why can they be portals of entry?

They line body cavities open to the environment and provide moist, warm environments where pathogens can enter.

What is the most common site of entry through mucous membranes?

The respiratory tract, with entry through the nose, mouth, or eyes.

What must gastrointestinal pathogens survive to cause infection?

The acidic pH of the stomach.

How does the placenta protect against pathogens?

It typically forms an effective barrier, although some pathogens can cross it and infect the fetus.

What is adhesion?

The process by which microorganisms attach to host cells using specialized structures or attachment molecules.

What happens if a microorganism cannot produce attachment proteins or adhesins?

It becomes avirulent according to the lecture slides.

What is the difference between signs and symptoms?

Symptoms are subjective experiences felt by the patient; signs are objective findings observed or measured by others.

What is a syndrome?

A group of signs and symptoms that characterize a disease or abnormal condition.

What are Koch's postulates?

1. Find the pathogen in every case of the disease. 2. Isolate it in pure culture. 3. Use it to infect a healthy host and reproduce the disease. 4. Re-isolate the same pathogen from the newly infected host.

What is pathogenicity versus virulence?

Pathogenicity is the ability of a microorganism to cause disease; virulence is the degree of pathogenicity.

What are the major virulence factors?

Adhesion factors, biofilms, extracellular enzymes, toxins, and antiphagocytic factors.

What are antiphagocytic factors?

Factors that protect pathogens from being engulfed by phagocytes; capsules can be slippery and difficult for phagocytes to engulf.

What do extracellular enzymes do?

They help pathogens maintain infection, invade tissues, and avoid body defenses.

What is toxemia?

The presence of toxins in the bloodstream.

What is the difference between endotoxins and exotoxins?

Endotoxins are lipid A, part of lipopolysaccharide in the outer cell wall of Gram-negative bacteria; exotoxins are proteins released as metabolic products by Gram-positive or Gram-negative bacteria.

How do endotoxins and exotoxins differ in toxicity?

Endotoxins are less toxic and can cause aches and fevers; exotoxins are very toxic and can be fatal.

What are the five stages of infectious disease?

Incubation, prodromal period, illness, decline, and convalescence.

What are the three general modes of infectious disease transmission?

Contact, vehicle, and vector transmission.

What are the types of contact transmission?

Direct contact, indirect contact through fomites, and droplet transmission.

What is vehicle transmission?

Transmission through nonliving materials such as air, water, food, or bodily fluids.

What is the difference between biological and mechanical vectors?

Biological vectors host part of the pathogen's life cycle; mechanical vectors passively carry pathogens on their bodies.

What is incidence?

The number of new cases of a disease in a given area during a given period of time.

What is prevalence?

The total number of cases of a disease in a given area during a given period of time.

What is the difference between endemic, sporadic, epidemic, and pandemic?

Endemic: consistently present in a region. Sporadic: occurs irregularly and infrequently. Epidemic: sudden, significant increase in cases, usually localized. Pandemic: disease spread over a wide area, such as multiple countries.

What is an exogenous nosocomial infection?

A healthcare-associated infection caused by a pathogen acquired from the healthcare environment.

What is an endogenous nosocomial infection?

A healthcare-associated infection caused by a pathogen arising from the patient's own normal microbiota.

What is the U.S. Public Health Service?

A national public health agency; the CDC is one of its branches.

What is the World Health Organization (WHO)?

An organization that coordinates public health efforts worldwide.

How does the skin protect the body against pathogens?

The skin acts as a physical barrier; pathogens may enter through cuts, openings, or by burrowing into or digesting its outer layers.

What is a superinfection?

An infection that occurs when antimicrobial drugs suppress some normal microbiota, allowing other microorganisms to thrive.

What is an iatrogenic infection?

A healthcare-associated infection that results from modern medical procedures.

What is foodborne transmission?

Spread of pathogens in or on contaminated food.

What is waterborne transmission?

Vehicle transmission commonly involving fecal-oral spread of pathogens through contaminated water.

What is airborne transmission?

Vehicle transmission in which pathogens travel more than one meter through an aerosol.

How do mucous membranes protect the body against pathogens?

They line body cavities that open to the environment, but their moist, warm conditions can also provide an environment for pathogens.

How does the placenta protect against pathogens?

It typically forms an effective barrier, although some pathogens can cross it and infect the fetus.

What are biofilms?

Communities of microorganisms attached to a surface and often surrounded by a protective material.

What are the three types of infectious disease reservoirs?

Animal reservoirs, human carriers, and nonliving reservoirs such as soil, water, and food.

What are human carriers?

People who carry and can transmit pathogens, even when they do not show symptoms.