DNA PCR Technology:Its Importance In Avian and Exotic Medicine

When it comes to performing diagnostic tests on avian and exotic animal patients, deciding which tests to perform under differing circumstances can be very confusing and challenging. Now, labs offer different tests for the same disease; for example, if you want to test a bird for chlamydiosis (psittacosis, Parrot Fever), you have the choice of performing chlamydial isolation (the gold standard, but may get false negatives), EBA titer (measures IGM, best for early infection), IFA titer (measures IGG, better for chronic infections and follow-up testing), DNA PCR testing (of a pooled choanal/cloacal swab, which detects the organism in the secretions), and DNA PCR testing of the blood (which detects the organism in the bloodstream). Choosing the correct test is very important in obtaining an accurate diagnosis, since there are many variables that can affect the outcome.
While most veterinary laboratories offer DNA PCR testing, there is often some confusion as to when this technology should be used in place of other testing methods. To better understand when and why to use DNA PCR tests, let's go over the basics of how this test works. PCR stands for polymerase chain reaction. PCR testing can be used to amplify the production of highly specific DNA fragments of Chlamydial, Mycoplasmal or viral genomes. This makes PCR testing both highly sensitive and highly specific. PCR testing can also be used to identify the sex of a bird, as well, by amplifying a portion of the W or Z chromosome, however the primers for sexing are generally species-specific. (The most widely used DNA method for sexing is called restricted fragment length polymorphism, RFPL, which is also extremely accurate).
By amplifying specific portions of the genome of a disease in combination with an avian probe, it is possible to identify specific disease strains. The major disadvantage to this technology is its extreme sensitivity. It is possible to contaminate a blood sample with organism particles from the skin or a toenail. For this reason, it is vital that the blood sample be procured aseptically and from a clean venipuncture stick. A toenail clip should never be used for the blood sample, since it is impossible to adequately disinfect the toe and nail to prevent contamination of the specimen, which may result in false-positive results. Tubes used for sample submission should be stored to prevent potential contamination. Often, bullet tubes are used, and these are supplied with the caps open. It is possible for environmental dust from a clinic to contaminate these tubes, which may also result in false positive test results. Make sure to store these tubes in sealed plastic bags, and close the caps for storage, as well.