Practice tip — March and April 2001

Practice tip

Maximizing the Diagnostics Potential of SIV Antigen Capture

Harry Snelson, DVM

Manager, Technical Services, Schering-Plough Animal Health

When faced with clinical respiratory disease in swine, it is es-sentialto rapidly establish the cause so that appropriate treatment can be implemented. One method currently available to diagnose swine influenza uses an ELISA test, produced for human diagnostic laboratories, to detect all type A influenza viral antigens. This kit, manufactured by Becton-Dickinson, is easy to use with either nasal swabs or tissue samples and requires no special equipment, and testing can be performed at the farm or in the office. The cost per sample is approximately $15, and the test takes less than 30 minutes to perform. Test kits can be ordered from numerous distributors, or from Centaur, PO Box 25667, Overland Park, Kansas 66225-5667, 913-390-6184. The price varies according to the number of tests ordered. Kits have a shelf life of 6 to 9 months.

Nasal swab samples are a relatively easy antemortem diagnostic method. Collection technique and selection of the proper animal to swab is critical in maximizing the test’s usefulness. The following tips should enhance the test kit’s diagnostic potential.

• Swab only febrile animals with temperatures of at least 40C (104F). The ability to capture viral antigen with this test is significantly reduced in non-febrile animals.
• Select animals exhibiting a clear, mucoid, non-purulent nasal discharge.
• Use polyester or Dacron tipped swabs (no cotton swabs). Swabs can be purchased from numerous suppliers (Fisher Scientific, 800-766-7000).
• If possible, clean any organic matter from the snout prior to sampling.
• Aseptically swab the walls of the nasal cavity. Swabbing should be done aggressively but gently to minimize the presence of blood on the swab. Blood and organic matter may decrease the accuracy of the test.
• Swab samples should be placed in a sterile blood collection tube containing a small amount of liquid medium (sterile saline, phosphate buffered saline solution (PBS), or non-chlorinated tap water) to keep the swabs moist, with a maximum of 2 swabs per blood tube. The swabs should be kept cool (on ice or refrigerated) if not tested immediately, but should be tested as soon as possible after collection.
• If testing tissue samples, Dr. Gene Erickson at Rollins Animal Disease Diagnostic Laboratory (Raleigh, North Carolina) recommends that the sample be chopped finely using a scalpel blade, not a blender, to avoid sample liquefaction. The sample should then be placed in a small amount of liquid medium or PBS in a Whirl-pak^(TM) bag, and the suspension should be allowed to settle before the test sample is collected from the supernatant.
• Sample at least ten animals exhibiting the signs outlined above.

This test is an effective and rapid method of respiratory disease diagnosis for your producers. A positive result enables you to quickly start appropriate treatment and management alterations. When an outbreak of swine influenza occurs in a herd, this test will be most successful at identifying positive animals when the suggestions listed above are followed carefully, and when nursery-to-finish animals, rather than adult breeding swine, are selected for testing.