New and Improved Diagnostic Testing Capabilities for EHD/BTV Now Available at the Texas Veterinary Medical Diagnostic Laboratory
The Significance of Hemorrhagic Disease in White‐Tailed Deer
Hemorrhagic Disease is an important infectious disease of white‐tailed deer (WTD). Outbreaks occur almost every year in Texas. It is caused by either of two closely related viruses, epizootic hemorrhagic disease (EHD) virus or bluetongue virus (BTV). Most cases of hemorrhagic disease observed in WTD can be attributed to EHDV serotype 1 or 2. However, since the recent occurrence of new serotypes in Texas, the current prevalence of EHD or BTV serotypes in
WTD populations is not clear.
The mode of transmission of EHD/BTV in nature is via a Culicoides biting fly or midge. Hemorrhagic disease should be suspected in instances of unexplained deer mortality during late summer or early fall, especially if any of the characteristic signs or lesions are noted. Clinical signs of EHD and BTV are very similar. Because of its very high mortality rate, EHD can have a significant effect upon the deer population in a given area, reducing numbers drastically. A combination of case history, characteristic signs and lesions, detection of nucleic acid and the isolation of the virus are necessary for a diagnosis of EHD. A strong tentative diagnosis can be made on the basis of gross and histological lesions characterized by hemorrhage in several organs.
The Development and Improvement of EHD/BTV Diagnostics at TVMDL
The Texas Veterinary Medical Diagnostic Laboratory (TVMDL) has developed and improved diagnostic techniques for the rapid identification, isolation and typing of EHD/BTV. Virus isolations are routinely performed using tissue culture. TVMDL has modified the isolation protocol to increase the efficiency of isolation and viral growth. The laboratory is developing primary cell cultures from WTD origin in order to evaluate their performance. Fresh specimens are essential for virus isolation because the viruses are killed as tissues decompose. Preferred specimens for virus isolation are refrigerated whole blood in anticoagulant containers and refrigerated or spleen, lymph node, liver, kidney, lung, and bone marrow. Isolation success is very poor with improperly preserved tissues and from deer dead more than 24 hours.
Real time Polymerase chain reaction (PCR) is a method that allows exponential amplification of short DNA sequences within a longer double stranded DNA molecule. This assay enables both detection in real time and quantification of a specific sequence in a DNA sample. TVMDL has developed a new Real‐Time PCR assay that detects all eight serotypes of EHD virus. This will facilitate disease surveillance and alert if other serotypes exotic to US may be present.
Together with real time PCR, TVMDL has recently acquired a specialized instrument that determines the order of the nucleotide bases along a DNA and provides the capability for typing EHD virus isolates. Continuous monitoring and characterization of EHD viral isolates currently circulating will allow to gain a greater understanding of the epidemiology and evolution of Hemorrhagic Disease in WTD and its’ potential for spread in the US.
For more information, contact:
Tammy Beckham, DVM, Ph.D. Director
Texas Veterinary Medical Diagnostic Laboratory
Tel. 979‐845‐3414
tbeckham@tvmdl.tamu.edu
http://tvmdl.tamu.edu
Alfonso Clavijo, DVM, Ph.D.
Assistant Agency Director for Diagnostic Programs
Texas Veterinary Medical Diagnostic Laboratory Tel. 979‐845‐3414
aclavijo@tvmdl.tamu.edu
http://tvmdl.tamu.edu
Don Davis, Ph.D.
Associate Professor Department of Pathobiology
College of Veterinary Medicine and Biomedical Science
Texas A&M University
Tel. 979‐845‐5174
DDavis@cvm.tamu.edu
http://www.cvm.tamu.edu/