Important Definition Epidemiology 

Antibody: A protein produced by an animal's immunological system in response to exposure to a foreign substance (antigen). Sometimes anti­bodies are produced against the individual's own proteins, causing autoimmune disease. Antibodies display specificity to particular antigens.

• Antigen: A substance (usually a protein) that induces a specific immune response.

• Biosecurity: Management-practice activities that reduce the opportunities for infectious agents to gain access to, or spread within, a food animal production unit.

• Carrier:  an animal that is infected with an infectious agent without displaying clinical signs, and that can be a source of infection to other animals;

• Case: an animal in a population or study group identified as having a particular disease or other health-related event that is being investigated.

• Case-control study: an observational study in which a group of diseased animals (cases) is compared with a group of non-diseased animals (controls) with respect to exposure to a cause.

• Cohort study: an observational study in which a group of animals exposed to a hypothesized cause is compared with a group not so exposed, with respect to development of a disease.

• Commensals: microbes found on the skin or within the body that do not usually cause disease.

• Cross-sectional study: an observational study in which animals are classified according to presence or absence of disease, and presence or absence of exposure to a causal factor, at a particular point in time.

• Determinant: a factor that affects the health of a population.

• Endemic: It is the occurrence of a diseases in a herd at an expected level

1. the predictable level of occurrence of disease, infection, antibody, etc.;

2. the usual presence of disease, infection, antibody, etc.

• Epidemic: an occurrence of disease in excess of its anticipated frequency

• Epidemiology (veterinary): the investigation of disease, other health-related events, and production in animal populations and the making of inferences from the investigation to improve the health and productivity of the populations

• Extrinsic incubation period: the time between the entry of an infectious agent into an arthropod vector and the time at which the arthropod becomes infectious.

• Fomites (singular: fomes): inanimate communicators of infection.

• Horizontal (lateral) transmission: transmission of an infection from an individual to any other individual in a population, but excluding vertical transmission

• Inapparent infection: an infection that does not produce clinical signs.

• Incidence: the number of new cases that occur over a specified period of time. It is usually expressed in relation to the population at risk and the time during which the population is observed.

• Longitudinal study: a study that records events over a period of time.

• Monitoring: the routine collection of information on disease, productivity and other characteristics possibly related to them in a population.

• Morbidity: the amount of disease in a population (commonly defined in terms of incidence or prevalence).

• Mortality: a measure of the number of deaths in a population.

• Multifactorial disease: a disease that depends on the presence of several factors for its induction. Most diseases are multifactorial, although some may have one major component cause (e.g., foot­and-mouth disease virus is the cause of foot-and­mouth disease), in which case they are commonly termed 'unifactorial'.

• Nidality: the characteristic of an infectious agent to occur in distinct nidi associated with particular geographic, climatic and ecological conditions.

• Nidus (plural: nidi): a focus of infection.

• Pandemic: a geographically widespread (sometimes global) epidemic. Occurrence of a disease in a wide geographical area.

• Pathogen: an organism that produces disease.

• Pathogenicity: the ability of an infectious agent to cause disease.

• Point (common) source epidemic: an epidemic resulting from exposure of animals to a single common cause.

• Prevalence: the number of occurrences of disease, infection, antibody presence, and so on in a population, usually relating to a particular point in time; it is commonly expressed as the proportion of the population at risk.

• Reservoir: an animate or inanimate object on or in which an infectious agent usually lives, and which therefore is often a source of infection by the agent.

• Sample: a selected part of a population.

• Screening: the identification of unrecognized disease or defect in an apparently healthy population

• Sensitivity (of a test): the proportion of diseased animals (true positive animals) that are detected by a test.

• Specificity: the proportion of non­diseased (true negatives) animals that are detected by a test.

• Sporadic: the irregular, unpredictable occurrence of disease or infection. Occurrence of a disease irregularly and haphazardly.

• Surveillance (veterinary): the on-going systematic collection and collation of useful information about disease, infection, intoxication or welfare in a defined animal population, closely integrated with timely analysis and interpretation of this information, and dissemination of relevant results to those requiring them, including those responsible for control measures.

• Surveillance is the collection, collation, analysis and dissemination of data.

• Survey: an investigation involving the collection of information and in which a causal hypothesis usually is not tested (d. Study). It may suggest aspects worthy of study.

• Vector: a living organism (frequently an arthropod) that communicates an infectious agent from an infected to a susceptible animal.

• Vertical transmission: transmission of an infection from one individual to its offspring. Virulence: the disease-evoking power of an infectious agent in a particular host.