To the Irish March 17 was St. Patrick’s Day, but for me it was a major milestone for VMRD and for me personally. We received a USDA product license for our Caprine Arthritis-Encephalitis Virus Antibody Test Kit, cELISA, the culmination of many years of careful research and development. This assay in my opinion is the best serodiagnostic test in the world today for CAEV infection of goats.
If one types the acronym "CAEV" on the search line of PubMed, 251 citations appear going back to 1980. Many of them describe diagnostic tests for CAEV serology. So why do I think VMRD’s new cELISA is the best? It has to do with the long history of the research organizations and people involved in the development of this assay. If one types in names of people I know who were directly involved in development of this assay and CAEV, a total of 89 citations appear. The point is that those involved in the development of this assay have played a major role in what is known and published about CAE.
Tim Crawford started the CAE project in the early 1970s when he was alerted to a rheumatoid arthritis-like disease in a herd of Toggenberg goats by the owner, a savvy physician’s wife named Betty Gustafson. Linda Cork, under Tim’s tutelage and whose committee included such distinguished scientists as Bill Hadlow and John Gorham, worked on leukoencephalitis which occurred among young goats in the same herd. It was thought to be viral because lesions could be produced with a filtrate injected intra-cerebrally. However, no virus was isolated.
The other clinical presentation in the index herd was chronic arthritis. It was not necessarily thought that the two conditions were related. Tim obtained grants from the Kroc Foundation and NIH to try to determine the etiology of the arthritis in part because it was clinically and histologically quite similar to rheumatoid arthritis. I was his graduate student on the project and Travis McGuire was a member of my graduate committee.
After multiple explants of goat synovial membranes from affected animals, syncytia were observed in a flask of cells taken from a Toggenberg Buck named Victory (G63). Cytopathic effect and indirect immunofluorescence indicated that we had isolated a viral agent. Reverse transcriptase assays performed by Phil Cheevers, buoyant density and electron microscopy confirmed that it was a retrovirus. Paula Klevjer-Andersen worked out the in-vitro biology of the isolate. The isolate was called 79-63 virus. In vivo experiments with the isolate confirmed Koch’s Postulates. The pathogenesis and immune responses of experimentally-induced disease were worked out. (3&4)
The clinical disease was characterized and an agar gel immunodiffusion assay was developed to determine seroprevalence. Morbidity of clinical arthritis in adult goats was much higher than the leukoencephalitis of kid goats so we changed the name to CAE. All of this happened before 1981.
Scrolling forward to 2001-2003, two publications came out of Don Knowles’ laboratory describing reactivity of monoclonal antibodies to the gp135 surface envelope glycoprotein (SU) of CAEV isolate 79-63 (CAEV-63) and use of VMRD’s cELISA which is based upon two of those monoclonal antibodies (7).
The cELISA’s performance was compared to gp135/90 SU/TM protein immunoprecipitation (IP) which is considered the gold standard for detection of antibodies to CAEV viral antigens. Two hundred goat sera collected from the United States were tested by IP and the cELISA. Sensitivity and specificity of the cELISA against IP were 100% and 96.4%, respectively. To analyze the possibility that the cELISA was more sensitive and not less specific than IP, sequential sera from eight experimentally-infected goats were tested by both assays. The cELISA detected antibody in seven of the eight goats before IP, indicating that it is more sensitive than IP.
A field study was carried out by three independent university-associated veterinary diagnostic laboratories located in the eastern, central and western areas of the United States. Four hundred sixteen samples obtained by the participating laboratories were tested by these laboratories with the cELISA and compared to results from a USDA-licensed agar gel immunodiffusion (AGID). Discorrelates were refereed by IP.
Against AGID, the cELISA had 14 false negatives and 20 false positives. Twenty-four of these samples had sufficient volume for IP analysis. Immunoprecipitation results agreed with the cELISA on 23 of the samples. The single sample agreeing with AGID was a negative, but remember that the cELISA was more sensitive than IP on the experimental infections.
A panel of 50 samples (24 positive and 26 negative) was also tested by the laboratories to determine tester interdependency. All three laboratories scored 100% correct results, indicating the field robustness of the cELISA.
Questions or Comments on this article? Scott Adams, President of VMRD, Inc., may be reached by e-mail at scott@vmrd.com
References:
1Cork LC, Hadlow WJ, Crawford TB, Gorham JR, Piper RC. Infectious leukoencephalomyelitis of young goats. J Infect Dis. 1974 Feb;129(2):134-41.
2 Crawford TB, Adams DS, Cheevers WP, Cork LC. Chronic arthritis in goats caused by a retrovirus. Science. 1980 Feb 29;207(4434):997-9.
3 Adams DS, Crawford TB, Klevjer-Anderson P. A pathogenetic study of the early connective tissue lesions of viral caprine arthritis-encephalitis. Am J Pathol. 1980 May;99(2):257-78.
4 Adams DS, Crawford TB, Banks KL, McGuire TC, Perryman LE. Immune responses of goats persistently infected with caprine arthritis-encephalitis virus. Infect Immun. 1980 May;28(2):421-7.
5 Crawford TB, Adams DS. Caprine arthritis-encephalitis: clinical features and presence of antibody in selected goat populations. J Am Vet Med Assoc. 1981 Apr 1;178(7):713-9.
6 Ozyoruk F, Cheevers WP, Hullinger GA, McGuire TC, Hutton M, Knowles DP. Monoclonal antibodies to conformational epitopes of the surface glycoprotein of caprine arthritis-encephalitis virus: potential application to competitive-inhibition enzyme-linked immunosorbent assay for detecting antibodies in goat sera. Clin Diagn Lab Immunol. 2001 Jan;8(1):44-51.
7 Herrmann LM, Cheevers WP, McGuire TC, Adams DS, Hutton MM, Gavin WG, Knowles DP. Competitive-inhibition enzyme-linked immunosorbent assay for detection of serum antibodies to caprine arthritis-encephalitis virus: diagnostic tool for successful eradication. Clin Diagn Lab Immunol. 2003 Mar;10(2):267-71.
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