HOST IMMUNOGENETICS PREDICT CLINICAL DISEASES IN OVINE PROGRESSIVE PNEUMONIA VIRUS INFECTED SHEEP
Location: Animal Diseases Research
Title: Evaluation of a Caprine Arthritis-Encephalitis Virus/Maedi-Visna Virus Indirect Enzyme-Linked Immunosorbent Assay in the Serological Diagnosis of Ovine Progressive Pneumonia Virus in U.S. Sheep
Submitted to: Clinical and Vaccine Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 5, 2009
Publication Date: February 1, 2010
Citation: Hoesing, L.M., Broughton-Neiswanger, .L., Gouine, K., White, S.N., Mousel, M.R., Lewis, G.S., Marshall, K.L., Knowles Jr, D.P. 2010. Evaluation of a Caprine Arthritis-Encephalitis Virus/Maedi-Visna Virus Indirect Enzyme-Linked Immunosorbent Assay in the Serological Diagnosis of Ovine Progressive Pneumonia Virus in U.S. Sheep. Clinical and Vaccine Immunology. 17(2):307-310.
Interpretive Summary: A new diagnostic test for the detection of the small ruminant lentiviral infections including ovine progressive pneumonia virus (OPPV), maedi-visna virus (MVV), and caprine arthritis-encephalitis virus (CAEV) was evaluated in U.S. sheep. This new diagnostic test named the CAEV/MVV indirect enzyme-linked immunosorbent assay (iELISA) offers quick result turnaround time (90 minutes), low numbers of false positive and negative results, and can be acquired in the U.S. with a permit. Therefore, we evaluated this CAEV/MVV iELISA on 299 U.S. sheep sera using the agar gel immunodiffusion (AGID) and radio-immunoprecipitation (IP) assays as gold standards. Our results showed that the CAEV/MVV iELISA had a sensitivity (Sn) of 88.2% and a specificity (Sp) of 95.4% as compared to either the AGID or the radio-IP assay. Furthermore, we evaluated this CAEV/MVV iELISA against a U.S. commercially available CAEV competitive ELISA (cELISA) on 405 Idaho sheep sera, and these results yielded a positive concordance of 92.9% and a negative concordance of 99.3%. Reduced similarity between the MVV strain EV1, which is utilized in the CAEV/MVV iELISA, and U.S. OPPV strains is thought to contribute to the overall reduced Sn and reduced positive concordance of the CAEV/MVV iELISA. This CAEV/MVV iELISA does not have adequate Sn in U.S. sheep sera, and therefore, it should not be utilized as a stand-alone diagnostic test for OPPV in U.S. sheep.
Serological diagnostic testing of sheep and goats using enzyme immunosorbent assays (ELISAs) is the most common method of determining small ruminant lentivirus (SRLV) infection. A caprine arthritis-encephalitis virus (CAEV)/maedi-visna virus (MVV) indirect (i) ELISA, which utilizes MVV EV1 capsid and a transmembrane peptide, was validated on U.S. sheep sera using OPPV WLC1 in radio-immunoprecipitation (IP) and OPPV WLC1 in agar gel immunodiffusion (AGID) as the comparable standards. By calculating a new cut-off percent value of 30.4 for U.S. sheep sera based upon the comparable standards, the sensitivity of the iELISA increased from 74% (95% confidence interval (CI)=7.6) to 88.2 (CI=5.4) whereas the specificity slightly decreased from 98.3 (CI=2.0) to 95.4 (CI=3.1). Furthermore, the positive and negative concordance of the iELISA using the new cut-off as compared to a CAEV cELISA on sera from an Idaho flock were 92.9% (CI=43.1%) and 99.3% (CI=1.4%). Of the 19 cELISA positive/iELISA negative discrepant samples, seventeen were confirmed as positive using OPPV WLC1 antigen on western blot analyses; whereas, the one cELISA negative/iELISA positive discrepant sample was confirmed as negative on western blot analyses. A lower mean percent nucleotide identity in gag encoding capsid between Idaho sheep and MVV EV1 (83.5±0.4) as compared to Idaho sheep and WLC1 (89.5±0.5) suggests that strain differences account for the lower sensitivity of the iELISA using U.S. sheep sera. This study indicates the importance in determining the breadth of viral strains in countries or geographical regions prior to developing a potential worldwide-accepted serological assay for small ruminant lentiviruses.