A team of faculty and staff at Colorado State University’s Veterinary Diagnostic Laboratories, and the Colorado Division of Wildlife, recently completed the first in-depth field validation and assessment of the Bio-Rad rapid test for chronic wasting disease in deer and elk. Detailed in the July issue of the Journal of Veterinary Diagnostic Investigation, the team analyzed more than 25,000 tissue samples and determined that the Bio-Rad test is an excellent rapid test for screening large numbers of samples to detect CWD in deer and elk populations.
According to researchers, Bio-Rad Laboratories’ enzyme-linked immunosorbent assay, or brELISA, is an effective and efficient CWD rapid test procedure for diagnosing brain and lymphoid tissue samples. The rapid brELISA takes five hours to complete compared to the three to five days necessary for the previously used Immunohistochemistry test, or IHC. Diagnosticians at the Veterinary Diagnostic Laboratory can test 990 tissue samples per day with the rapid test compared to 260 per day with the IHC.
Additionally, the new study shows that the rapid test is comparable in accuracy to IHC, considered the "gold standard" of CWD testing.
"IHC is a costly, labor-intensive and time-consuming technique necessitating skilled histology technicians and pathologists to diagnose CWD," said Barbara Powers, director of Colorado State’s Veterinary Diagnostic Laboratory. "The rapid brELISA designed for large-volume sample screening is a very effective and practical solution to meet the increased demand for CWD testing and surveillance. It is faster, requires fewer personnel, allows for automation and larger daily volumes of samples, and is less expensive."
The two-phase study was a collaborative effort among Colorado State’s Veterinary Diagnostic Laboratories, the Colorado Division of Wildlife, the Colorado Department of Agriculture and the Colorado Veterinary Medical Association. Biologists and veterinarians collected nearly 30,000 samples from more than 27,000 deer and elk and examined them for CWD during the entire 2002 hunting seasons in Colorado. The objectives of the study were to determine how the testing performance of brELISA compared with the proven IHC in detecting CWD, and then to evaluate the use of the rapid test in a large-scale CWD surveillance program.
"Field validation studies provide an opportunity to obtain valuable information regarding the accuracy of new tests and to examine the pitfalls facing analysis on a large scale," said Powers.
For the initial validation phase, Veterinary Diagnostic Laboratory researchers examined 4,175 samples independently by brELISA and IHC. Overall agreement between the two tests was nearly 100 percent for lymph nodes. Based on these results, the Bio-Rad rapid test to detect CWD in deer and elk was granted a license by the United States Department of Agriculture for use nationwide in November of last year.
During the phase 2 field application, researchers studied the effectiveness of the rapid test on a large-scale; an additional 20,875 tissue samples were tested for CWD. For this phase, the Immunohistochemistry test was only used to confirm positive brELISA results. The rapid brELISA proved to be equally as sensitive, specific and reliable in the larger field application as in the validation tests.
The Colorado Division of Wildlife and diagnosticians at Colorado State’s Veterinary Diagnostic Laboratory, with facilities in Fort Collins, Grand Junction and Rocky Ford, expect to test up to 40,000 deer and elk samples for CWD in 2003 using the Bio-Rad rapid CWD test. In addition, Bio-Rad’s second generation CWD test, recently approved by the USDA, was also validated at Colorado State’s Veterinary Diagnositc Laboratory. The new test, called the TeSeE test kit, was designed to run on an automated Bio-Rad designed robotic system that automates a portion of the testing procedure, speeds up sample preparation and enables laboratories to provide faster results using fewer technicians. Colorado State’s Veterinary Diagnostic Laboratory was the first laboratory in the world to use the new robotic system to screen CWD samples.
A testing system for CWD was established last year for the collection of hunter-killed samples of elk and deer. Colorado hunters may submit deer and elk carcasses to the Division of Wildlife at sample collection sites or to participating veterinarians from the Colorado Veterinary Medical Association. Tissue samples are extracted and sent to Colorado State for diagnosis using the rapid rest for detection of possible CWD infection.