Acute infection - shows their symptoms immediately and dissipates quickly.

Antibody - proteins created in blood and tissue by the immune system to help neutralize and destroy possible threats.

Antigen - a toxin or enzyme which stimulates reactions from a body's immune system.

Antigenicity - The ability of an antigen to combine with antibodies and T-cell receptors to invoke a reaction from the immune system.

Autoimmune diseases – diseases caused when the immune system turns on itself because it fails to recognize its own cells.

B lymphocyte cells - bursa-dependent; manufactured in the bone; identify antigens and produce antibodies.

Bacteriophages - viruses that infect and kill harmful bacteria.

Base pair - a twin pair of nucleotides contained in a nucleic acid strand, which are linked together by hydrogen bonds.

Body fluids - fluids of the body, including circulating blood and lymph, the chyle, the gastric, pancreatic, and intestinal juices, the saliva, bile, urine, aqueous humor, and muscle serum

Budding - mature viruses leave a cell slowly, a few at a time, not killing the host cell in the process.

Bursa - a tissue space lined by joint tissue; bursas are found in between tendon and bone, skin and bone and muscles.

Carrier - one who carries a virus either in form of an infection or while it is in incubation.

Caspid - The protein outer covering of a virus made up of capsomeres; stimulates the body's immune response.

Cell - a small, enclosed unit containing the DNA, proteins, and chemicals needed for all life functions.

Chromosomes - a DNA containing body that holds most or all of the genes of an individual life form.

Chronic infection - recurring viral infections that cause damage of cells over a long period of time by disrupting their functions.

CNS - the central nervous system, which is comprised of nerves, the brain and the spinal cord.

Connective tissue - tissue that surrounds other more highly ordered tissues and organs; blood, cartilage and bone.

Cytoskeleton - protein filaments that extend through the cytoplasm of cells and enable them to move and change shape.

DNA - deoxyribonucleic acid, the basic component of all living matter, which is contained in the chromosomes of a cell's nucleus; transmits hereditary information and contains gene sequences.

Differentiated - a type of cell, which specializes in one specific task or has one specific purpose.

Dormant - being in a state of suspended animation, not actively growing but protected from the environment.