SK320, U1, Introduction

The study of the underlying cause of a disease

Disease caused by an infectious agent that can be transmitted from person to person; by contact, formites, air, water etc.

Data collected over a short period to give a snapshot of disease occurrence in a specific place at a specific time. Can be compared if collected like-for-like.

Social characteristics often recorded in population statistics; age, sex, ethnic group, education level etc.

A measure of how much quality of life a population has lost to a disease through premature death, chronic disease and disability. (?The sum of mortality and morbidity due to a disease)

Infectious diseases that are permanently present in a population because there is always a sufficient reservoir of susceptible individuals.

An outbreak of an infectious disease in a community or region, characterised by a sharp increase in the number of cases. (See pandemic also)

• An estimate of the number of healthy (disease-free) years that individuals born in a particular year, based on current trends in health, can expect to live.
• This figure is then used to calculate HALE, for populations as a whole, for each sex and for different age groups.

An animal that has pathogenic microbes or multicellular parasites living in or on its body, or which belongs to a species that commonly harbours them.

• Adaptations in an individual's immune system that lead to increased resistance to subsequent infections with a particular pathogen after initial exposure to it. 
• A person is immune if these adaptations prevent them from succumbing to the disease again.

The scientific study of the cells and molecules of the immune system and their actions in the body, particularly but not exclusively in response to infection.

The number of new cases of a disease arising in a given period, usually a year, expressed as a proportion of the population at risk (incidence rate).

• Principles which determine whether a microorganism or infectious agent caused a disease;
• 1. The organism is regularly found in the lesions of the disease.
• 2. It can be isolated in a pure culture on artificial media.
• 3. Inoculation of the culture produces a similar disease in experimental animals.
• 4. The organism can be recovered from lesions in these animals.

One in which pathogens persist in or on a host's body, but without producing symptoms; during the latent period, the host may or may not be infectious.

Data collected routinely from the same place or region at successive intervals (often annually), in order to identify changing trends in the occurrence of disease over time.

Microscopic organisms (bacteria, fungi, protists), together with viruses and infectious prions, whether pathogenic of harmless; also known as microorganisms.

A measure of the deaths in a population at risk, usually expressed as a rate of the population.

An epidemic on a world-wide scale

A single-celled or multicellular organism that lives in or on the body of a larger organism (it's host), deriving benefits from this arrangement and causing harm to the host.

A disease-causing microbe; pathogenic bacteria, fungi, viruses and prions.

A usually fatal epidemic disease, especially used to describe plague.

The proportion of the population with a particular infection or disease at a particular point in time, or during a given period.

Non-human hosts of a zoonotic pathogen

The complete elimination by the host's immune response of the pathogen responsible for an infectious disease (e.g. the influenza virus is eliminated from the body as the illness resolves)

Routinely collected statistics, stored in regional national or international databases, on episodes of specific diseases, disorders or disabilities (morbidity) and on deaths from specific causes (mortality). Data from many sources.

Anyone in a population who is not immune to a particular pathogen or parasite, and is thus capable of developing the infectious disease that is causes.

Infectious diseases which can be prevented or reduced to a low incidence level, by vaccination programmes that include a sufficiently high proportion of a population; globally the term generally includes diptheria, whooping cough, tetanus, mumps, polio, TB.

Infectious diseases caused by pathogens or parasites transmitted to humans via insects (mosquitoes, tsetse flies), or other invertebrates (snails). Infected individuals are not infectious to other people; some vector-borne diseases also have a reservoir of infection in non-human vertebrates (they are zoonoses).

• Infectious disease caused by pathogens or parasites transmitted to humans from their principal reservoir in another vertebrate species (rodents, monkeys, antelope, poultry, cattle).
• Transmission can occur through direct contact or via an intermediate vector (flies or lice). 
• Once established in a human population, the causative agents of some zoonoses (pneumonic plague, pulmonary TB), can also be transmited directly between humans.