2 Disease Transmission, Progression, and Immunity

Vocabulary terms and definitions covering microbial habitats, symbiotic relationships, disease types, transmission mechanisms, pathogenesis, immunity, and epidemiology based on the lecture notes.

Microbiome

All the microorganisms and their genetic material living in a specific environment, such as the gut, skin, or a pond.

Extremophiles

Microbes that live in extreme environments.

Thermophiles

Microbes that live in very hot places, such as hot springs and deep-sea vents.

Psychrophiles

Microbes that live in very cold places, such as glaciers, snow, and permafrost.

Rhizosphere

The soil directly around plant roots where plants release sugars to attract bacteria that help absorb nutrients like nitrogen and phosphorus.

Community

A group of different microorganisms living together in the same environment.

Microbial ecology

The study of microbial populations and how they interact with each other and their environment.

Symbiosis

A close relationship between different species.

Mutualism

A symbiotic relationship where both organisms benefit.

Commensalism

A symbiotic relationship where one organism benefits while the other is not affected.

Parasitism

A symbiotic relationship where one organism benefits while the host is harmed.

Resident microbiota

Microbes that normally live in or on the body long-term, such as normal bacteria in the gut, skin, or vagina.

Transient microbiota

Microbes that are only present temporarily and may include pathogens picked up from touching contaminated surfaces.

Infectious disease

A disease caused by a pathogen, such as influenza.

Communicable disease

An infectious disease that can spread from person to person.

Contagious disease

A communicable disease that spreads easily, such as measles.

Iatrogenic disease

A disease caused by a medical procedure, such as an infection from a contaminated catheter.

Nosocomial disease

An infection acquired in a healthcare setting, such as hospital-acquired pneumonia or a surgical-site infection.

Zoonotic disease

A disease spread from animals to humans, such as rabies or Lyme disease.

Noncommunicable infectious disease

A disease caused by a pathogen but not spread person-to-person, such as tetanus from soil entering a wound.

Noninfectious disease

A disease not caused by a pathogen; it may be caused by genetics, environmental factors, or immune problems.

Portal of exit

The route a pathogen uses to leave an infected host and spread, such as the mouth, nose, urinary tract, or blood.

Vector

An animal that carries a pathogen from one host to another.

Mechanical vector

An animal that carries a pathogen on the outside of its body without becoming infected.

Biological vector

An animal in which a pathogen lives or reproduces before being transmitted to another host.

Direct contact transmission

Spread of a pathogen through physical contact, such as touching, kissing, or sexual contact.

Vertical direct contact transmission

Mother-to-child transmission during pregnancy, birth, or breastfeeding.

Horizontal direct contact transmission

Person-to-person transmission that is not from mother to child.

Droplet transmission

Respiratory droplets spread by coughing or sneezing over a short distance, usually within $1\text{ meter}$.

Indirect contact transmission

Spread of a pathogen through a contaminated object, called a fomite.

Fomite

A nonliving contaminated object, such as a doorknob, needle, or towel, that can transmit pathogens.

Vehicle transmission

Spread of a pathogen through a nonliving material such as food, water, or air.

Reservoir

The normal place where a pathogen lives and survives; can be living (humans, animals) or nonliving (soil, water).

Passive carrier

A person who is not infected but carries a pathogen and can transfer it, such as a healthcare worker with contaminated hands.

Active carrier

An infected individual who can spread a pathogen, whether they show symptoms or not.

Asymptomatic carrier

An individual who is infected and contagious but has no symptoms.

Definitive host

The host in which a parasite reaches sexual maturity.

Intermediate host

The host in which a parasite is immature or reproduces asexually.

Portal of entry

The body site where a pathogen enters, such as the skin, mucous membranes, or respiratory tract.

TORCH pathogens

A group of pathogens that can cross the placenta: Toxoplasmosis, Other (syphilis, chickenpox, etc.), Rubella, Cytomegalovirus, and Herpes.

Adhesion

The process when a pathogen attaches to host cells using surface molecules called adhesins.

Adhesins

Surface molecules that help pathogens bind to receptors on host cells; they are considered virulence factors.

Biofilms

Groups of bacteria attached to a surface and covered by a sticky protective layer called EPS, which protects them from immune defenses.

Invasion

When a pathogen spreads from the entry site into local tissue, deeper tissues, or the body.

Virulence factors

Traits that help pathogens cause disease by attaching, invading, damaging tissue, or avoiding immune defenses.

Intracellular pathogens

Pathogens that enter and reproduce inside host cells.

Phagocytosis

The process by which a phagocyte or white blood cell engulfs a pathogen.

Local infection

An infection that stays near the entry site, such as a boil or bladder UTI.

Focal infection

An infection that starts in one area but where pathogens or toxins spread to another site.

Systemic infection

An infection that spreads throughout the body, such as chickenpox.

Primary infection

The first infection caused by a pathogen.

Secondary infection

An infection that occurs because the first infection or treatment weakened the host's defenses.

Sign

An objective and measurable indication of disease, such as fever or abnormal blood pressure.

Symptom

A subjective feeling of disease felt by the patient, such as pain or nausea.

Syndrome

A specific group of signs and symptoms that occur together with a disease.

Incubation period

The period after a pathogen enters the body but before it causes signs or symptoms.

Prodromal period

The stage of disease where general signs and symptoms like fever, pain, or inflammation begin.

Period of illness

The stage where signs and symptoms of a disease are most obvious and severe.

Period of decline

The stage where pathogen numbers and symptoms decrease, leaving the patient weak and at risk for secondary infection.

Period of convalescence

The final stage where the body returns toward normal function.

Acute disease

A disease that develops quickly and lasts a short time, such as influenza.

Chronic disease

A disease that lasts months, years, or a lifetime, such as chronic gastritis or hepatitis B.

Latent disease

A disease where the pathogen becomes dormant without active replication and can reactivate later.

Antimicrobial peptides (AMPs)

Cell-made chemicals that damage microbial membranes, DNA, RNA, or cell-wall synthesis.

Acute-phase proteins

Proteins mainly made by the liver during inflammation that help inhibit or destroy microbes.

Complement system

A group of proteins that help with opsonization, inflammation, chemotaxis, and cytolysis.

Cytokines

Chemical messages released by cells to communicate and coordinate immune responses.

Chemokines

Cytokines that attract white blood cells to a site of infection, injury, or inflammation.

Interferons

Cytokines released by virus-infected cells that warn nearby cells and slow viral replication.

Histamine

An inflammatory chemical released by mast cells and basophils that increases blood flow and vessel permeability.

Leukotrienes

Strong inflammatory chemicals released by mast cells that can cause coughing, vomiting, or diarrhea.

Hematopoiesis

The process of making blood cells in the bone marrow.

Neutrophils

Granulocytes that are usually the first to arrive at bacterial infections to phagocytose and kill bacteria.

Natural killer cells

Agranulocytes that kill abnormal cells, including virus-infected and cancer cells, by causing apoptosis.

Macrophages

Phagocytes found in tissues that engulf pathogens and release cytokines.

PAMPs

Pathogen-associated molecular patterns; common microbial structures like peptidoglycan or LPS recognized by immune cells.

Morbidity

The state of being diseased.

Prevalence

The total number or proportion of people with a disease at one point in time.

Incidence

The number or proportion of new cases of a disease during a certain time.

Sporadic disease

A disease that occurs occasionally and in scattered locations, such as tetanus or the plague.

Endemic disease

A disease that is constantly present, usually at a low level, in a certain location.

Epidemic disease

A disease with more cases than expected in a short time in one area.

Pandemic disease

An epidemic spread worldwide, such as HIV/AIDS or COVID-19.

Emerging infectious disease

A disease that is new in humans or has been increasing in prevalence during the previous $20\text{ years}$.

Contact tracing

The process of finding and notifying people exposed to an infected person to interrupt the spread of disease.

Common source spread

A pattern where many people are infected from one shared source, such as contaminated food or water.

Propagated spread

A pattern where a disease spreads person-to-person without a single shared source.

Index case

The infected person first identified in a contact-tracing investigation.

Quarantine

The separation of people known or suspected to have been exposed to a contagious disease to monitor for illness.