Published by Australian Academy of Science
Glossary | Bird flu – the pandemic clock is ticking

antibiotic. A substance produced by bacteria or fungi that destroys or prevents the growth of other bacteria and fungi. Antibiotics are not effective against viruses.

antibody. A protein produced by the body’s immune system in response to a foreign substance (antigen). An antibody reacts specifically with the antigen that induced its formation and inactivates the antigen. Our bodies fight off an infection by producing antibodies.

antigen. Any foreign substance, usually a protein, that stimulates the body's immune system to produce antibodies. (The name antigen reflects its role in stimulating an immune response – antibody generating.)

antivirals. Drugs that are used to prevent or cure a disease caused by a virus, by interfering with the ability of the virus to multiply in number or spread from cell to cell.

carrier. Is a person who is infected with an agent that causes a disease who shows no sign of illness. Asymptomatic carriers shed the causative agent, such as a virus or bacteria, and so can pass the disease on to others. The most famous asymptomatic carrier was Mary Mallon, or Typhoid Mary.

contagious. A contagious disease is easily spread from one person to another by contact with the infectious agent that causes the disease. The agent may be in droplets of aerosols made by coughing or sneezing, contaminated food utensils, water or food.

cytokine. A hormone-like molecule, produced by one cell, that has an effect on another cell. Some types of cytokines are normally produced in low concentration by the immune system as part of the body’s defence mechanism. Some cytokines are toxic at high concentrations and cause disease symptoms such as fever.

enzyme. A protein that acts as a catalyst. Every chemical reaction in living organisms is facilitated by an enzyme.

epidemiology. The study of diseases or conditions in human populations and the factors that influence their incidence and prevalence.

gene. The basic unit of inheritance. A gene is a segment of DNA that specifies the structure of a protein or an RNA molecule.

genetic mutation. A change in the genetic material (DNA, or RNA in the case of some viruses) resulting in new or rearranged hereditary determinants. Mutations are rare, random events in which the base sequence of the nucleic acid molecule is changed. The frequency of mutations may be increased by chemicals or radiation.

haemagglutinin. A protein which forms a rod-shaped spike on the surface of influenza virus. The name haemagglutinin is given because the spikes are capable of adhering to red blood cells, causing them to be agglutinated (clumped).

host. An organism on or in which a parasite lives.

immune system. The cells, tissues and organs that assist the body to resist infection and disease by producing anitbodies and/or altered cells that inhibit the multiplication of the infectious agent.

neuraminidase. An enzyme which forms a mushroom-shaped projection on the surface of an influenza virus particle. The enzyme assists in the release of newly-formed virus particles from the surface of an infected cell.

nucleic acid. A large molecule made up of a sequence of phosphorylated nitrogen-containing bases. DNA and RNA are both nucleic acids.

pandemic. The worldwide outbreak of a disease.

prophylactic. A medical procedure or practice that prevents or protects against a disease or condition (eg, vaccines, antibiotics, drugs).

protein. A large molecule composed of a linear sequence of amino acids. This linear sequence is a protein's primary structure. Short sequences within the protein molecule can interact to form regular folds (eg, alpha helix and beta pleated sheet) called the secondary structure. Further folding from interaction between sites in the secondary structure forms the tertiary structure of the protein.

Proteins are essential to the structure and function of cells. They account for more than 50 per cent of the dry weight of most cells, and are involved in most cell processes. Examples of proteins include enzymes, collagen in tendons and ligaments and some hormones. More information can be found at Protein structure and diversity (Molecular Biology Notebook, Rothamsted Research, UK).

public health. The aspect of medical activity directed towards improving the health of the whole community.

species. Living things of the same kind that are potentially capable of breeding and producing fertile offspring. Theoretically, plants or animals of different species cannot interbreed. However, occasionally this does not hold true.

vaccine. A preparation consisting of antigens of a disease-causing organism which, when introduced into the body, stimulates the production of specific antibodies or altered cells. This produces an immunity to the disease-causing organism. The antigen in the preparation can be whole disease-causing organisms (killed or weakened) or parts of these organisms.

virulent. Highly lethal; causing severe illness or death.

virus. A submicroscopic infectious agent consisting of a nucleic acid (DNA or RNA) molecule surrounded by a protein coat. Viruses cannot replicate outside a living cell. More information can be found at How viruses work (How Stuff Works, USA).

zoonoses. Diseases that are transferable to humans from animals.