Ultimate Epidemiology Glossary

Acquired immunity - Immunity that is acquired either by contact with infection or through vaccination. An example of this is chicken pox.

Antibody - (aka immunoglobulin) A Y-shaped gamma globulin protein on the surface of B cells (lymphocytes that mature in the bone marrow) that are secreted into blood or lymph in response to an antigenic stimulus such as bacteria, virus, parasite, or transplanted organ. It deactivates the antigen by attaching to it. Each antibody latches exclusively onto a specific antigen, which it then deactivates. Large heavy chains and small light chains are characteristic of an antibody.

Antigen - Substance when introduced into the body stimulates production of an antibody. Antigens can include toxins, bacteria, foreign blood cells, and cells of transplanted organs.

Anthelmintics - Drugs that expel or destroy parasitic worms from the body.

Arbovirus – Any of the various rNA viruses transferred predominantly via arthropods, such as mosquitoes and ticks. Diseases transmitted in this manner include yellow fever, encephalitis, malaria, and dengue.

Bacteremia - The presence of bacteria in the blood, generally transient in nature. Bacteria can enter the bloodstream through wounds, infections, injections, or surgical procedures. 

BIDE – Birth, Immigration, Death, Emigration. The 4 demographic parameters that determine population growth.

Breakpoint – Point of discontinuity, adjustment, or termination occurring in reference to susceptibility and resistance to antibacterials.

Carrier - a person, animal, or plant that retains and propagates a specific agent as a microorganism, causing an infectious disease from which it has recovered and to which it is immune. Also an entity that possesses a unique gene which is capable of transmitting to offspring but not of showing its typical expression.

Co-evolution -Two or more species that have a close ecological relationship and evolve together, adapting to the other’s changes and influencing each other’s evolution. The species are not necessarily mutually dependent on one another for survival. It can be either a predator-prey, host-parasite, or mutual relationship. 

Contact rate - The rate at which susceptibles, those having little resistance to a specific infectious disease, meet infecteds, host with an infection. It is usually measured as individuals per unit time.

Contagious distribution – Bacterial and fungal diversity.

Crude birth rate - The number of live births divided by the average population multiplied by 1000.

Crude death rate - The number of deaths in a year divided by the population size multiplied by 1000.

Definitive host - The host in which a parasite evolves into an adult or the sexually mature stage. This is also known as the final host.

Density-dependent – A factor that influences individuals in a population to a degree that varies in response to how dense the population is.

Direct life cycle - The life cycle in which a parasite is transmitted directly from one host to the next without an intermediate host or vector of another species.

Disease - an impairment of the normal state of the living animal or plant body or one of its parts that interrupts or modifies the performance of the vital functions and is a response to environmental factors, such as malnutrition, industrial hazards, or climate, to specific infective agents, such as worms, bacteria or viruses, to inherent defects of the organism as in genetic anomalies or to combinations of these factors.

Epidemic - Affecting or tending to affect an atypically large number of individuals within a population, community, or region at the same time.

Epidemic fadeout - Parasite extinction occurring because numbers are so low immediately following an epidemic.

Herd immunity - Resistance of a group to a pathogen due to immunity of a large proportion of the group to that pathogen.

Holoendemic - Affecting all or characterized by the infection of essentially all of the inhabitants of a particular region.

Immunity - A condition of being able to resist a particular disease especially through preventing development of a pathogenic microorganism or by counteracting the effects of the pathogen.

Immunogenicity - The state of generating an immune response.

Immunopathology - A branch of medicine dealing with immune responses associated with disease. Also the pathology of an organism, organ system, or disease with respect to the immune system, immunity, and immune responses.

Immunosuppression - Suppression of natural immune responses.

Infection - The state produced by the establishment of an infective agent in or on a suitable host.

Infectious period - The time period during which those infected are able to transmit an infection to any susceptible host or vector they contact. The infectious period may not necessarily be associated with symptoms of the disease.

Inoculum - Material used for inoculation.

Latent period - The period between exposure to a disease-causing agent or process and the appearance of symptoms.

Mass action transmission - Transmission of infection which occurs at a rate directly proportional to the number or density of both susceptibles and infecteds present.

Maternal immunity - Protection against disease that is acquired by a fetus through the passage of maternal antibodies via the placenta.

Mesoendemic – An endemic disease that affects a moderate proportion of the population at risk.

Mortality rate - The proportion of deaths in a population or to a specific number of the population. The ratio of deaths in an area to the population of that area as expressed per 1000 per year.

Pandemic - Occurring over a wide geographic area and affecting an exceptionally high proportion of the population.

Panzootic - A disease affecting animals of many species, especially over a wide area.

Parasite - An organism living in, with, or on another organism in parasitism.

Pathogen - Specific causative agent, such as bacteria or virus, of disease.

Prevalence - Percentage of a population that is affected with a particular disease at a given time.

Serology - Science dealing with serums, specifically their reactions and properties.

Seroprevalence - The frequency of individuals in a population that have a particular element, i.e. antibodies to HIV, in their blood serum.

Serotype - A group of intimately related microorganisms distinguished by a common set of antigens.

Stochastic model - A mathematical model involving random variables in order to estimate probability distributions of potential outcomes. Relating to or characterized by random chance or probability.

Transmission - An act, process, or instance of transmitting.

Transmission breakpoint -A critical average worm burden below which is the mating frequency is too low to maintain a dioecious (hermaphroditic) parasite species, for example, the tapeworm.

Transmission threshold - Occurs for a parasite when the basic reproductive rate R0 =1. Below this threshold level the disease is unable to maintain itself within the host population..

Vaccine - A preparation of either nonliving microorganisms, live, weakened organisms, or live, fully virulent organisms, generally given as an inoculation, that is administered to produce or artificially increase immunity to a specific disease over a period of time.

Viraemia - The presence of virus in the blood of a host.

Virion - A single virus particle, complete with a coat protein.

Virulence - The relative capacity of a pathogen to overcome body defenses.

Zoonosis - A disease communicable from animals to humans under natural conditions. An example includes Salmonella and reptiles.