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Glossary

This glossary has been compiled to help familiarize readers with some basic terminology used in such disciplines as climatology, ecology, medicine, and public health. It is not meant to be a comprehensive or definitive glossary for any of these fields.

Agent (of disease): Factor such as a microorganism whose presence is essential for the occurrence of a disease.

Albedo: Measure of the reflecting power of an object (e.g., Earth), expressed as the proportion of incident light it reflects.

Anthropogenic: Caused or produced by humans.

Anthroponosis: Infection that causes disease in nonhuman hosts but that can be perpetuated solely in human hosts (e.g., malaria).

Association: Statistical dependence between two or more events, characteristics, or other variables. The presence of an association does not necessarily imply a causal relationship.

Case fatality ratio: Cumulative incidence of death in a group of individuals who develop a particular disease over a specific time period.

Climate: Average meteorological conditions over a specified time period, usu-



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Page 110 Glossary This glossary has been compiled to help familiarize readers with some basic terminology used in such disciplines as climatology, ecology, medicine, and public health. It is not meant to be a comprehensive or definitive glossary for any of these fields. Agent (of disease): Factor such as a microorganism whose presence is essential for the occurrence of a disease. Albedo: Measure of the reflecting power of an object (e.g., Earth), expressed as the proportion of incident light it reflects. Anthropogenic: Caused or produced by humans. Anthroponosis: Infection that causes disease in nonhuman hosts but that can be perpetuated solely in human hosts (e.g., malaria). Association: Statistical dependence between two or more events, characteristics, or other variables. The presence of an association does not necessarily imply a causal relationship. Case fatality ratio: Cumulative incidence of death in a group of individuals who develop a particular disease over a specific time period. Climate: Average meteorological conditions over a specified time period, usu-

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Page 111 ally at least a month, resulting from interactions among the atmosphere, oceans, and land surface. Climate variations occur over a wide range of spatial and temporal scales. Disease, communicable: Illness caused by a specific infectious agent; arises through transmission of that agent or its products from an infected person, animal, or reservoir to a susceptible host. Dose-response relationship: Relationship in which a change in the amount, intensity, or duration of exposure is associated with a change in the risk of a specified outcome. Ecosystem: Mutually interrelated communities of species and abiotic components, existing as a system with specific interactions and exchange of matter, energy, and information. El Niño: A warming of the surface waters of the tropical Pacific that occurs every three to five years, temporarily affecting weather worldwide. Endemic: Restricted or peculiar to a locality or region. Endemic infection refers to a sustained, relatively stable pattern of infection in a specified population. Epidemic: Appearance of an abnormally high number of cases of infection in a given population. Epidemiology: Study of the distribution and determinants of health-related states or events in specified populations. Epidemiology is the basic quantitative science of public health. Epizootic: An epidemic in an animal host population. Extrinsic incubation period: Time required for the development of a disease agent in a vector from the time of uptake of the agent to the time when the vector is infective. Herd immunity: Mechanism by which an infection may be eradicated from a population, although some susceptibles still remain, because the remainder of the population is immune and thus transmission is reduced. Host (disease): Person or other living animal that affords subsistence or lodgment to an infectious agent under natural conditions. Immunity: Condition of protection against infectious disease conferred either

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Page 112 by the immune response generated by immunization or previous infection, or by other non-immunological factors. Incidence: Number of cases of a disease commencing, or of persons falling ill, during a given period of time in a specified population. Incidence rate is the number of new cases of a specific disease diagnosed or reported during a defined interval of time divided by the number of all persons in a defined population during the same time. Infection: Presence of a parasite in a host, where it may or may not cause disease. Infection, reservoir of: Any person, animal, arthropod, plant, soil or combination of these in which an infectious agent normally lives and multiplies, on which it depends primarily for survival, and where it reproduces itself in such a manner that it can be transmitted to a susceptible host. Infectivity: Characteristic of the disease agent that embodies the capability to enter, survive, and multiply in the human host. Meta-analysis: Process of using statistical methods to combine the results of different studies. Miasma theory: An explanation for the origin of epidemics, based on the notion that when the air was of a so-called bad quality, persons breathing it would become ill. Microclimate: In climatology, defined as localized climate, incorporating physical processes in the lowest 100 to 2,000 meters of the atmosphere. In ecology, defined as climatic conditions in the environmental space occupied by a species, a community of species, or an ecosystem. Mitigation: Initiatives that reduce the risk from natural and man-made hazards. With respect to climate change, mitigation usually refers to actions taken to reduce the emissions or enhance the sinks of greenhouse gases. Model, mathematical: Representation of a system, process, or relationship in mathematical form in which equations are used to simulate the behavior of the system or process under study. Morbidity: State of ill health produced by a disease; rate of occurrence of disease in a population.

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Page 113 Outbreak: Localized occurrence as opposed to a generalized epidemic. Pandemic: Epidemic that occurs over a very wide area. Pathogen: Organism capable of causing disease. Pathogenicity: Frequency with which an organism produces disease. Pathogenicity of an infectious agent is measured by the ratio of the number of persons developing clinical illness to the number exposed to infection. Prevalence: Proportion of persons in a population that is currently affected by a particular disease. Prevalence rate is the number of cases of a specific disease at a particular point in time divided by the population at that time living in the same region. Risk: Probability that an event will occur; a measure of the degree of loss expected by the occurrence of an event. Risk assessment: Qualitative or quantitative estimation of the likelihood of adverse effects that may result from exposure to specific health hazards. Scenario building: Method of predicting the future that relies on a series of assumptions about alternative possibilities, rather than on simple extrapolation or existing trends. Southern Oscillation: A large-scale atmospheric and hydrospheric fluctuation centered in the equatorial Pacific Ocean; exhibits a nearly annual pressure anomaly, alternatively high over the Indian Ocean and high over the South Pacific; the variation in pressure is accompanied by variations in wind strengths, ocean currents, sea surface temperatures, and precipitation in the surrounding areas. Susceptibility: Probability that an individual or population will be affected by an external hazard, such as infection by a pathogen. Teleconnections: Statistical relationship between the El Niño/Southern Oscillation (ENSO) cycle and rainfall or temperature anomalies observed in a particular geographical location. Transmission: Process by which a pathogen passes from a source of infection to a new host. Vector: An organism, such as an insect, that transmits a pathogen from one host to another.

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Page 114 Vectorial capacity: Average number of potentially infective bites transmitted by one vector species from one infective host in one day. Virulence: Degree of pathogenicity; disease-evoking power of a microorganism in a given host. Numerically, the ratio of the number of cases of overt disease in the total number infected. Vulnerability: Extent to which a population is liable to be harmed by a hazard event. Depends on the population's exposure to the hazard and its capacity to adapt or otherwise mitigate adverse impacts. Weather: Condition of the atmosphere at a particular place and time measured in terms of wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation. In most places, weather can change from hour to hour, from day to day, and from season to season. Zoonosis: Infection that causes disease in human populations but that can be perpetuated solely in nonhuman host animals (e.g., bubonic plague).