Definitions of terms as used in this manual
|
Absorption |
The movement of a fluid or a dissolved substance across a membrane. |
|
Adsorption |
The process whereby a layer of molecules, atoms or ions attach to the surface of a red blood cells. |
|
Agglutination |
A specific reaction whereby viruses link together microscopic foreign particles such as red blood cells. This causes visible clumping. |
|
Antibody |
A protein produced by the immune system in response to an antigen. The antigen can be an infectious agent for example Newcastle disease virus. |
|
Antigen |
Any substance, usually a protein, that causes an antibody response when introduced into the body. Antigens also react with antibodies in serological tests. |
|
Bifurcates |
Divides into two branches. |
|
Biosecurity |
Precautions taken to minimize the risk of introducing an infectious agent into a population. |
|
Elution |
The detachment of virus from the receptors on the surface of red blood cells. |
|
50% Embryo Infectious Dose (EID50) |
Reciprocal of that dilution of virus per unit volume that results in infection of 50 percent of the inoculated embryos. See Section 13 |
|
50% Embryo Lethal Dose (ELD50) |
Reciprocal of that dilution of virus per unit volume that results in the death of 50 percent of inoculated embryos. |
|
Endpoint |
The point in an assay where the highest dilution of the substance being tested produces a positive result. |
|
Haemagglutination (HA) |
The agglutination or clumping of red blood cells by virus. A diffuse film is formed on the well of a microwell plate as the virus-red blood cell complex settles under gravity. |
|
Haemagglutination Inhibition (HI) |
Mixing a serum sample with Newcastle disease virus antigen resulting in specific binding between anti-Newcastle disease virus antibodies in the serum and the Newcastle disease virus. The binding sites on the virus particles that attach to red blood cells are no longer free for binding and haemagglutination is therefore inhibited. The red blood cells roll to the bottom of the V-bottom wells of microwell plates and form a distinct button. |
|
Haemagglutination Inhibition Titre |
The reciprocal of the highest or last two-fold dilution where haemagglutination inhibition is detected. |
|
Haemolysis |
The destruction of red blood cells and release of haemoglobin. |
|
Hyperaemia |
Increased blood supply to a part of a body. The blood remains in vessels and does not haemorrhage. |
|
Isotonic |
A solution that causes no change in the state or tone of cells for example red blood cells when they are stored in DGV storage solution. |
|
I-2 Master seed |
A collection of uniform aliquots of the I-2 strain of Newcastle disease virus from which all other seed passages are derived. |
|
I-2 Working seed |
A collection of uniform aliquots of the I-2 strain of Newcastle disease virus produced by passage of the I-2 master seed. Used to prepare the I-2 Newcastle disease vaccine. |
|
Labile |
Unstable and readily changes. |
|
50% Lethal dose (LD50) |
Reciprocal of that dilution of virus per unit volume that results in the death of 50 percent of inoculated susceptible chickens. |
|
Lysis |
Disintegration. |
|
Lentogenic |
Low virulence. |
|
Mesogenic |
Moderate virulence. |
|
Mean death time (MDT) |
The time taken for a minimal lethal dose of Newcastle disease virus to kill chicken embryos. |
|
Passage |
The subculture of Newcastle disease virus in embryonated eggs. |
|
Pathotype |
A term used to designate virulence of isolates of Newcastle disease virus. |
|
Proteases |
Enzymes that digest proteins. |
|
Pleomorphism |
Occurring in many shapes. |
|
Seed lot |
A term used in vaccine production to describe a system where the original master seed virus is multiplied, harvested and stored in aliquots. This is referred to as the working seed. These aliquots are then multiplied to produce vaccine. This system minimizes the number of passages of virus needed to produce vaccine and reduces the risk of genetic change and of contamination. |
|
Thermolabile |
Sensitive to and changed by heat. |
|
Thermostable |
Exhibiting a relative resistance to inactivation on exposure to elevated temperatures. |
|
Titration |
A procedure used to measure the concentration of a substance in a solution. |
|
Velogenic |
High virulence. |
