Thanks to Artie McDonald for sending in the lead about this article.
CAE, Caprine Arthritis Encephalitis, a virus, has long been a thorn in the side of meat and milk producers. This disease impacts the bottom line through lost production due to arthritis, progressive paresis, and other neurologic and musculoskeletal disfunction. Testing has traditionally been directed toward detection of serum antibodies produced by the goat's immune system.
The University of Colorado has recently completed a comparison of serologic diagnosis (using the usual AGID testing kits) to genome level testing for CAE. This new test is known as polymerase chain reaction or "PCR". The following information is extracted and developed from their web site article on this issue http://www.cvmbs.colostate.edu/dlab/webdocs/general/lablines7.pdf.
Please note that the link above provides a PDF file and that a pdf reader such as the free Adobe Acrobat Reader must be installed on your computer to view the file.
The investigation team sampled groups of animals from four infected sheep herds and performed both tests.
An animal was considered positive only if either PCR or AGID gave positive results.
Number of Animals in Results Categories Comparing AGID to PCR for OPP/CAE Diagnosis
PCR Test Results
PCR detected 4 sheep that were AGID negative.
AGID detected 5 sheep that were PCR negative.
The study criteria resulted in a PCR sensitivity of 89 percent and an AGID sensitivity of 91 percent.
Neither test detected all infected animals.
The recommendations of the report writer, Jim Collins, are
- For eradication and control purposes, both tests should be used.
- AGID screening could be performed first since it is less expensive, followed by PCR testing of the negative animals.
- Multiple testing of animals (at least two) should be performed with either test over a period of several months.
Fees and sample submission guidelines:
AGID test: $5.00 - Submit one ml (cc) serum.
PCR test: $22.00 - Submit blood in EDTA tube.
Now... past all the technical stuff - Opinion of the editor:
The new test seems to be an adjunct to, not a replacement for, the existing method. The study sample size was just barely sufficient to obtain statistically significant results.
The significance of the results could be placed in question by the "justifications" given for the false negatives of both methods.
The existing test, though less expensive, was more accurate than the new evaluation method.
- The four (4) AGID false negatives were justified by stating that the subject animals had reduced antibody levels due to age.
- The five (5) PCR false negatives were justified by stating that other viruses might have the same genetic sequences.
It seems inappropriate to this writer that a test should be touted as an improvement in method over one which performed better in the laboratory study.
The use of the PCR test as a secondary level of testing seems valid for highly suspect herds where the anticipated level of infection is high.
In commercial herds that have a lower risk the cost of "back up" testing with the PCR method would be prohibitive except for the most highly valued animals.
Breeding stock, show animals, and dairy production goats, however, present an entirely different level of concern. The purchase of these higher valued animals should be accompanied by every possible assurance that they are free from disease of any kind. I would recommend that such animals be tested utilizing both methods before purchase. If the seller does not provide the service the buyer would be wise to shoulder the cost themselves.
The results of the study belie the title of the University of Colorado report. "Eradication of OPP or CAE..." does not seem a good choice for the title of a report showing no improvement over pervious methods. With 26 of 73 highly suspect study animals showing negative results in both tests we have a long journey ahead of us before we achieve "eradication".