Source: IDEXX Poultry & Livestock Catalog and ELISA Technical Guide
The ELISA (enzyme-linked immunosorbent assay) is a rapid test used for detecting and quantifying antibodies or antigens against viruses, bacteria and other materials. This method can be used to detect many infectious agents affecting poultry and livestock.
In ELISA technology, the solid phase consists of a 96-well polystyrene plate, although other materials can be used. The function of the solid phase is immobilized either antigens or antibodies in the sample, as they bind to the solid phase. After incubation, the plates are washed to remove any unbound material. Conjugate is then added to the plate and allowed to incubate.
The conjugate consists of either an antigen or antibody that has been labeled with an enzyme. Depending upon the assay format, the immunologically reactive portion of the conjugate binds with either the solid phase or the sample. The enzyme portion of the conjugate enables detection.
The plates are washed again and an enzyme substrate (hydrogen peroxide and a chromogen) is added and allowed to incubate. Colour develops in the presence of bound enzyme and the optical density is read with an ELISA plate reader.
ELISAs are divided into three main formats – indirect, blocking (competitive) and antigen-capture (direct).
In the indirect format, the sample antibody is sandwiched between the antigen coated on the plate and an enzyme-labeled, anti-species globulin conjugate. The addition of an enzyme substrate-chromogen reagent causes colour to develop. This colour is directly proportional to the amount of bound sample antibody. The more antibody present in the sample, the stronger the colour development in the test wells. This format is suitable for determining total antibody level in samples.
Blocking (Competitive) Format
In this format, the specific sample antibodies compete with, or block, the enzyme-labeled, specific antibody in the conjugate. The addition of an enzyme substrate-chromogen reagent causes colour to develop. This colour is inversely proportional to the amount of bound sample antibody. The more antibodies present in the sample, the less colour development in the test wells.
Antigen-Capture (Direct) Format
In the antigen-capture format, the antigen in the sample is sandwiched between antibodies coated on the plate and an enzyme-labeled conjugate. The antibody conjugate can either monoclonal or polyclonal. The addition of an enzyme substrate-chromogen reagent causes colour to develop. This colour is directly proportional to the amount of the target antigen present in the sample.
VFAD offers the following ELISA screening tests:
• Avian Encephalomyelitis (AE)
• Avian Influenza Virus
• Avian Leukosis Virus Subgroup J
• Chicken Anaemia Virus (CAV)
• Infectious Bronchitis Virus (IBV)
• Infectious Bursal/Gumboro Disease Virus (IBD)
• Infectious Laryngotracheitis (ILT)/Herpesvirus
• Mycoplasma gallisepticum (MG)
• Mycoplasma synoviae (MS)
• Newcastle Disease Virus (NDV)
• Ornithobacterium rhinotracheale (ORT)
• Pasteurella multocida
• Reovirus/Avian Viral Arthritis
• Salmonella Group B and Salmonella Group D
• Swollen Head Syndrome (SHS)/Avian Pneumovirus (APV)
• Foot and Mouth Disease Virus-Cattle, Sheep, Goats & Pigs
• Aujeszky’s Disease
• Classical Swine Fever Virus (CSF)
• Foot and Mouth Disease Virus-Swine (FMD)
• Mycoplasma hyopneumoniae
• Porcine Reproductive and Respiratory Syndrome Virus (PRRS)
• Porcine Circovirus Type-2 (PCV2)
• Swine Influenza Virus
• Total Aflatoxin