Hemorrhagic Diseases of White-tailed Deer (continued)
Detection
A sensitive in vitro host system identified for EHDV is BHK-21 cells. If the virus has been suitably amplified by one passage in cell culture, it can be detected/characterized by the immunoperoxidase assay; otherwise a second passage in BHK-21 cells may be necessary.
Once the virus is isolated, it is further characterized and identified in an immunoperoxidase assay using monoclonal antibodies. This assay will determine if the orbivirus isolated is BTV or EHDV. Further confirmation of virus serotype can then be performed by virus neutralization tests.
In addition, a rapid test for viral nucleic acid detection (BTV or EHDV) can be performed using the real time polymerase chain reaction (RT-PCR) on the original samples submitted. This test is highly sensitive and specific and results can be obtained after few hours.
Serological tests can be used during an outbreak to determine the etiology, after the initial outbreak, to determine the spread of the disease, and as part of a continuous surveillance program. However, where the disease is endemic little or no value can be obtained from a single serological testing.
In an outbreak, serum (submitted along with tissues and whole blood) would be tested for BTV/EHDV antibodies by the AGID test or by a competitive ELISA. The AGID is not highly specific and occasionally, the presence of crossreacting antibodies to orbiviruses results in false positive results. However, the competitive ELISA can determine if the animals have been exposed to BTV and exclude EHDV or vice versa, and it is therefore the test of choice.