28th Annual Meeting and Symposium of the
Desert Tortoise Council, February 21-23, 2003
Abstracts

Validation of the ELISA test for Herpesvirus Exposure Detection in Desert Tortoises: Options and Limitations

Francesco C. Origgi¹, April Johnson², and Elliott R. Jacobson^2
1Human Virology Unit, HSR Scientific Institute, Milano, Italy
²Department of Small Animal Clinical Sciences, University of Florida, Gainesville, FL

An Enzyme Linked Immunosorbent Assay (ELISA) was applied to the serological diagnosis of tortoise herpesvirus exposure in Greek and Hermann's tortoises (Testudo graeca and Testudo hermanni). Subsequently, it was validated through a transmission study in Greek tortoises. The ELISA was statistically as reliable as serum neutralization test (SN), which is traditionally considered to be the gold standard test for serological diagnosis of viral infection. Recently, the ELISA test was used to determine exposure of desert tortoises (Gopherus agassizii) to tortoise herpesvirus. Despite preliminary data that suggested a positive correlation between the ELISA test results and those obtained by polymerase chain reaction (PCR) specific for tortoise herpesvirus sequences, the ELISA test still needs to be validated for use in desert tortoises. Ideally, a transmission study in desert tortoises would be the best approach for validation. The principal obstacle to this possible approach is the lack of a herpesvirus isolate from a desert tortoise. Until a desert tortoise isolate is available for use as an antigen in the test, another approach could entail the use of Western blots in parallel with the ELISA test. While Western blots are known to have a lower sensitivity than ELISA tests, they have a higher specificity. This diagnostic protocol is commonly used in human medicine to confirm that a positive ELISA is truly positive. The use of PCR on plasma samples could be a further confirmatory test. However its use would be limited to those infected tortoises that are also viremic.