BIOM-3070 Week 4 - Infection, Infectious Diseases and Epidemiology

Symbiosis

The "living together" of microbes and their host; types are mutualism, commensalism, amensalism, and parasitism

Mutualism

Type of symbiosis where both the microbe and the host benefit

Commensalism

Type of symbiosis where one partner benefits and the other is unaffected

Amensalism

Type of symbiosis where one partner is harmed and the other is unaffected

Parasitism

Type of symbiosis where one partner benefits at the host's expense; the main type studied in this course

Normal microbiota (normal flora)

Microbes that colonize the body's surfaces without normally causing disease; also called indigenous microbiota

Resident microbiota

Normal microbiota that stay with you throughout life; mostly commensal

Transient microbiota

Normal microbiota that remain in the body only a short time; they cannot persist because of competition, body defenses, or body changes

Microbiome acquisition

Babies are born essentially sterile; the microbiome begins during the birth process and resident microbiota are established during the first months of life

Opportunistic pathogen

A normal-microbiota microbe that causes disease under certain circumstances

When normal microbiota become opportunistic pathogens

When they are introduced into an unusual body site, when the immune system is suppressed, when normal microbiota levels/types change, or under stressful conditions

Reservoir of infection

A site where pathogens are maintained as a source of infection

Animal reservoir

Reservoir type in which pathogens are maintained in animals; diseases passed to humans are zoonoses

Zoonoses

Diseases that naturally spread from animal hosts to humans; acquired by direct contact or waste, eating animals, or bloodsucking arthropod vectors; humans are usually dead-end hosts, making them difficult to eradicate

Human carrier

An infected individual with no symptoms who can still infect others; some later become ill, others never do

Nonliving reservoir

Soil, water, and food acting as pathogen sources; presence of microbes is often due to contamination by feces or urine

Contamination

The mere presence of microbes in or on the body

Infection

When an organism evades the body's external defenses, multiplies, and becomes established in the body

Disease (morbidity)

What results when an invading pathogen alters normal body functions

Portal of entry

A site through which pathogens enter the body; the three major ones are skin, mucous membranes, and the placenta

Skin as a portal of entry

Its outer layer of dead cells is a barrier; pathogens enter through cuts or openings, or by burrowing in or digesting the outer layers

Mucous membranes as a portal of entry

They line body cavities open to the environment and give a moist, warm home; the respiratory tract is the most common entry site (nose, mouth, eyes); GI entry must survive stomach acid

Placenta as a portal of entry

Usually an effective barrier, but crossers such as Listeria monocytogenes can cause spontaneous abortion, birth defects, or premature birth

Parenteral route

Not a true portal of entry: pathogens are deposited directly into tissues beneath skin or mucous membranes, bypassing the usual portals (e.g. surgery, non-sterile needles)

Adhesion

The process by which microorganisms attach themselves to host cells; required to establish colonies successfully in the host

Adhesion factors (adhesins / ligands)

Attachment proteins on viruses and bacteria that bind host-cell receptors; the binding determines host-cell specificity; without them a microbe is avirulent

Avirulent

Unable to cause infection, e.g. when a microorganism cannot make attachment proteins (adhesins)

Symptom

A subjective characteristic of disease, felt only by the patient

Sign

An objective manifestation of disease that can be observed or measured by others

Syndrome

The set of symptoms and signs that characterize a disease or abnormal condition

Asymptomatic (subclinical) infection

An infection that lacks symptoms, though it may still have signs of infection

Etiology

The study of the cause of disease

Pathogenicity

The ability of a microorganism to cause disease

Virulence

The degree of pathogenicity of a microorganism

Virulence factors

Traits contributing to virulence: adhesion factors, biofilms, extracellular enzymes, toxins, and antiphagocytic factors

Stages of infectious disease (in order)

Incubation period, prodromal period, illness, decline, convalescence

Incubation period

Disease stage after infection with no symptoms yet; the first of the five stages

Prodromal period

Disease stage with early, vague symptoms; the second of the five stages