Location: Animal Disease Research2011 Annual Report
1a. Objectives (from AD-416)
(1) Determine the genetic organization and expression of Ovine MHC Class I, IIa, and IIb loci, (2) Determine and validate that specific MHC Class I and/or MCH Class II alleles associate with OPPV clinical disease phenotypes and, (3) Determine the functional significance and subsequent immune responses of MHC alleles that associate with OPPV clinical disease phenotypes.
1b. Approach (from AD-416)
OPPV is a sheep lentivirus that infects 24% of U.S. sheep flocks and causes economic losses to the sheep producer due to mastitis, dypsnea, and lameness. Serological diagnostic tests which test for the presence of anti-OPPV antibodies have provided a highly sensitive and specific means of testing but have not shown statistical correlations with pathology or other clinical markers of disease. Therefore, an OPPV test that predicts or determines which infected sheep will proceed to clinical disease progression is highly sought. Our laboratory is currently evaluating two different tests for the prediction or determination of OPPV clinical disease. One test is a quantitative PCR test utilizing real time technology, which targets a conserved region of the transmembrane protein of OPP provirus, and the second test is an immunogenetics test for MHC Class II DRB1. With one or both of these tests, we hope to provide a diagnostic OPPV test that determines or predicts whether the sheep will progress to OPPV clinical signs. In addition, these types of tests will significantly reduce the number of other tests necessary for determining infection and possibly lower the transmission potential in a flock. Therefore, these new tests offer significant long-term economic advantages for the producer over conventional serological diagnostic tests. Replacing 5348-32000-025-00D, April 2007.
3. Progress Report
In previous progress reports, Major Histocompatiblity Complex (MHC) class II DR Beta 1 (DRB1) and chemokine (C-C motif) receptor 5 (CCR5) gene variants associated with the control of ovine progressive pneumonia virus (OPPV) levels in the blood of sheep. Currently, MHC class II DRB1 gene variants are being evaluated in cell culture for OPPV controlling effects. Extending from these earlier gene variant studies, a whole genome scan was conducted on approximately 1200 sheep to investigate the association of various genetic markers with OPPV infection and control of OPPV levels. One marker associates with increased susceptibility to OPPV infection, and we are collaborating with two other ARS locations, U.S. Meat Animal Research Center and the U.S. Sheep Experiment Station, in writing, verifying and releasing this information. The next phase for this genetic research is to create a cell culture and live animal infection model that tests these genetic markers for OPPV susceptibility or resistance. In this report, we generated an aerosol nebulization experimental infection model in sheep. This aerosol nebulization infection model has similar sensitivity to the intravenous infection model, but better represents a natural transmission and challenge model. Sheep infected with OPPV are life-long carriers of the virus and serve as potential reservoirs in the transmission of OPPV. Therefore, identifying the main mode of OPPV transmission could help break the transmission and infection cycle. In this report, we also showed that maternal transmission accounts for 10-14% of transmission whereas non-maternal transmission account for the remaining 86-90%. Therefore, this result with other literature supports that separation of infected adults from uninfected adults serves as a good way of limiting transmission and infection. In this report, we also initiated a study with the University of Idaho Caine Veterinary Teaching Center (see 5348-32000-029-01S) to examine and quantitate bacterial flora, including Mannheimia haemolytica, in the nasal secretions of domestic sheep. New project 5348-32000-031-00D to start 10-1-11.
1. Maternal and non-maternal transmission of ovine progressive pneumonia virus (OPPV) was investigated in an Idaho ewe flock. Historically, OPPV was thought to be mainly transmitted to lambs by maternal means. To investigate this, viral sequences were compared between 35-40 dam-daughter sets. Interestingly, ARS scientists at Pullman, WA and Dubois, ID found that maternal transmission accounted for only 10-14% of transmission whereas non-maternal transmission accounted for the remaining 86-90% of transmission. Removal of lambs from OPPV infected dams to thwart infection in the flock is laborious and may not decrease transmission if the lambs are placed back into the flock after weaning. This data suggests that separation of adult OPPV infected ewes from uninfected ewes may significantly reduce transmission.
Broughton-Neiswanger, L.E., White, S.N., Knowles Jr, D.P., Mousel, M.R., Lewis, G.S., Herndon, D.R., Hoesing, L.M. 2010. Non-maternal transmission is the major mode of ovine lentivirus transmission in a ewe flock: A molecular epidemiology study. Infection, Genetics and Evolution. 10(7):998-1007.