Lecture 1: Epidemiology

Emerging infectious disease

Illnesses which are transmissible between people, from animals to people, from food, or in some cases inanimate objects such as hospital equipment, and that have the power to cause death or severe disease.

Communicable disease

Diseases that can be transmitted from one person to another.

Non-communicable disease

Diseases that cannot be transmitted between people.

Epidemic

A sudden increase in the number of cases of a disease above what is normally expected in a population.

Endemic

A disease or condition regularly found and consistently present in a particular geographic area.

Acute disease

A disease with a rapid onset and/or a short course.

Chronic disease

A long-lasting disease that can be controlled but not cured.

Infectious disease components

Agent, Transmission, Host, Environment.

Infectious disease agent

Includes viruses, bacteria, rickettsia, protozoan, helminthes, fungi, and arthropods.

Reservoir

A suitable environment to 'store' an agent, including humans, animals, vectors, or inanimate items.

Persistence

Ability of an organism to survive outside the host and resist destruction.

Latency

Stage of an agent in which it is not infectious, usually allowing it to survive outside the host.

Vector

Usually an arthropod that can directly or mechanically transmit an agent from host to host or environment to host.

Intermediate host

Some agents require a developmental stage in one or two species before they can infect the final host.

Virulence

Strains and species of the same organism have differing abilities to cause disease.

Direct transmission

Human to human; can involve an environmental component.

Autoinfection

Person contaminates themselves directly from their external orifices.

Indirect transmission

The agent can survive 'outside' the human host.

Zoonosis

Infections that are naturally transmitted between vertebrate animals and humans.

Domestic zoonosis

Infections from 'invited' animals which live in close proximity to humans.

Synanthropic zoonosis

Infections from animals that live in close association with humans but aren't invited.

Exoanthropic zoonosis

Infections from animals not in close association with humans.

Carrier state

Can be involved in both direct and indirect disease transmission.

Asymptomatic carrier

Demonstrate no outward clinical signs throughout the infection.

Prodromal carrier

Infectious but unaware they are in the early stages of infection.

Convalescent carrier

Continue to be infectious after clinical disease has passed.

Host susceptibility factors

Genetic, Age, Sex, Pregnancy, Resistance.

Environmental factors

Can influence both the transmission and host susceptibility of a disease.