MicroBio Vocabulary Terms

Infectious Disease

A clinically evident illness caused by the invasion and multiplication of pathogenic microorganisms (such as bacteria, viruses, fungi or parasites) in a host

Infection

The entry, establishment, and multiplication of microorganisms in the tissues of a host, which may or may not lead to disease

Asymptomatic Infection

An infection in which the host harbors a pathogen but shows no clinical signs or symptoms, although they may still transmit the organism

Colonization

The presence and growth of microorganisms on body surfaces (such as skin or mucosa) without causing tissue invasion or symptoms

One step in biofilm formation, possible virulence factor (E. coli)

Opportunistic Pathogen

A microorganism that usually does not cause disease in a health host but can cause infection when host defenses are compromised or normal flora is disrupted

Obligate Pathogen

A microorganism that almost always causes disease when it is present and cannot persist for long in the host or environment without causing pathology

Obligate Intracellular Pathogen

A pathogen that must live and replicate inside host cells because it cannot reproduce or carry out essential metabolic processes outside them

Viruses

Facultative Intracellular Pathogen

A bacterium that can survive and replicate both inside host cells and in the extracellular environment

The bacterium can hide from immune response inside host cells

Virulence Factor

Any microbial component or strategy (such as toxins, enzymes, adhesins or capsules) that contribute to the ability of a pathogen to cause disease

Localized Infection

An infection limited to one specific site or tissue in the body, without systemic spread

Systemic Infection

An infection that spreads through the bloodstream or lymphatics to multiple organs or tissues in the body

Nosocomial Infection

An infection acquired in a hospital or other healthcare facility that was not present or incubating at the time of admission

Acute Infectious Disease

An infection with a rapid onset of symptoms and a relatively short clinical course

Chronic Infectious Disease

An infection that develops more slowly and persists for months or years, often with periods of remission and relapse

Ex: HVS

Latent Infection

An infection in which the pathogen persists in the host in a dormant state with no symptoms, but can reactivate later to cause disease

Factors that reactivate it are stress, UV, antibiotics

Ex: Varicella-Zoster virus

Persistent Infection

A long-lasting infection in which the pathogen is continuously present in the host, sometimes at low levels, with or without ongoing symptoms

Typical in hospitals, immunocompromised patients

Incubation Period

Time between exposure to a pathogen and the onset of the first signs or symptoms

During this phase, the pathogen is multiplying and the host’s innate and adaptive immune responses are being activated but there is still no clinical disease

Prodromal Period

Early phase of an illness with nonspecific, mild symptoms (ex: malaise, low-grade fever) that appear as the immune response starts to intensify and tissue damage begins

Symptoms are often vague and diagnosis may be uncertain

Acute Phase

Period during which signs and symptoms are most intense and the pathogen load and inflammatory response are at their peak

Clinical manifestations are fully developed and the effect of antimicrobial or supportive treatment is usually most evident in reducing symptoms and pathogen burden

Convalescence Period

Recovery phase after the acute illness during which pathogen levels fall, the immune response contracts, and damaged tissues are repaired

Symptoms gradually resolve and the host returns to normal health, although some patients may still be infectious or feel residual fatigue

Clinical Cure

Resolution of the signs and symptoms of an infection as judged by the patient and clinician

Microbiological Cure

Eradication of the causative pathogen from the body, confirmed by negative microbiological tests

Symptom

A subjective complaint reported by the patient

Specific Symptom

A symptom that strongly suggests a particular disease

Ex: bloody diarrhea in Shigellosis

Nonspecific Symptom

A symptom that occurs in many different conditions

Ex: Fever, low-grade fever

Syndrome

A set or pattern of signs and symptoms that tend to occur together and characterize a particular disease or condition

Active Carrier

An infected individual who shows clinical signs and symptoms of disease and can transmit the pathogen to others, typically because they are shedding large numbers of microorganisms (Ex: in respiratory secretions, stools, or lesions)

Healthy Carrier

An individual who harbors a pathogen and can transmit it to others but has no clinical signs or symptoms

Infection is often controlled by the immune system, so the person feels well but still sheds the microorganism (Ex: in stool, saliva, or nasal secretions)

Chronic Carrier

A person who continues to harbor and shed a pathogen for months or years after apparent recovery from the acute infection

Focus (Source, Reservoir)

The site or environment where a pathogen normally lives, multiples and from which it can spread to susceptible hosts

Reservoirs can be human, animal or environmental

Biological Vector

An arthropod or other living organism that not only transports a pathogen but also supports part of its life cycle or replication before transmitting it to a new host

Vehicle

A non-living medium (food, water, or blood products) that passively carries pathogens from one host to another

Fomite

An inanimate object or surface that can become contaminated and serve as a source of indirect transmission of pathogens

Horizontal Transmission

Transmission of a pathogen between individuals of the same generation

Ex: Direct contact, droplets, sexual contact, vectors, or contaminated objects

Vertical Transmission

Transmission of a pathogen from parent to offspring, typically from mother to child, before, during, or shortly after birth

Congenital Transmission

Vertical transmission of a pathogen from mother to fetus across the placenta during pregnancy, leading to infection present at birth

Perinatal Transmission

Transmission of a pathogen from mother to child shortly before, during, or immediately after delivery (ex: during passage through the birth canal)

Postnatal Transmission

Transmission of a pathogen from mother or environment to the newborn after birth, for example through breast milk, close contact or respiratory droplets

Zoonosis

An infectious disease that is naturally transmitted between animals and humans

Immunization

Process of inducing or boosting protective immunity against a specific pathogen, usually by vaccination

Vaccination

Act of administering a vaccine containing antigens or attenuated/inactivated organisms to induce immunity

Antimicrobial Treatment

The use of drugs such as antibiotics, antivirals, antifungals, or antiparasitics to prevent or treat infections caused by microorganisms

Prophylaxis

Any intervention, such as vaccines or antimicrobial drugs, given to prevent infection or disease before exposure or early after exposure

Pathogenesis

The mechanisms and processes by which a pathogen cause disease in the host, from initial entry to tissue damage and clinical manifestations

Virulence

The relative ability of a microorganism to cause disease, often reflected in the severity of the infection it produces

Mechanism of Pathogenicity

The specific strategies and steps used by a microorganism to invade the host, evade defenses, damage tissues, and produce disease

Epidemiology

The study of the distribution, determinants, and control of health-related events, including infectious disease in populations

Incidence

The number of new cases of a disease that occur in a defined population during a specified period of time

Prevalence

The total number of cases of a disease (new and pre-existing) present in a defined population at a given point in time or over a specified period

Epidemic

An occurrence of disease cases in a community or region that is clearly in excess of the expected baseline level

Endemic

The constant presence or usual baseline level of a disease or infectious agent in a particular geographic area or population

Ex: Malaria in Africa

Pandemic

An epidemic that has spread over several countries or continents, usually affecting a large number of people

Ex: Covid-19 in 2020

Outbreak

A sudden increase in the number of cases of a disease in a particular time and place, often limited in scale but above the expected level

Ex: Adenovirus infection in one school