|Knowles Jr, Donald|
Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2006
Publication Date: 5/25/2007
Citation: Hoesing, L.M., Palmer, G.H., Knowles Jr, D.P. 2007. Evidence of proviral clearance following postpartum transmission of an ovine lentivirus. Virology. 362(1):226-234
Interpretive Summary: Lactogenic transmission has been considered the main source of ovine progressive pneumonia virus. This study investigated the efficiency of lactogenic transmission of ovine progressive pneumonia virus (OPPV) using 10 naturally OPPV-infected 6-year old gravid ewes. It was found that although the 10 OPPV-infected ewes were capable of transmitting virus to their respective 22 lambs, the 22 respective lambs cleared cell associated virus and for 4 years, none of the lambs have established persistent infection. Interestingly, a 3 year old unrelated ewe was placed with the OPPV infected ewes after lactation and developed persistent infection after 2+ years which showed that the OPPV was fully infectious. The passive transfer of anti-OPPV maternal antibody in the colostrum to the lambs may have contributed to the clearance of cell-associated OPPV in the lambs. In addition, cross neutralizing antibody was present in the colostrum which suggests that maternal antibody in the colostrum may lower the cell-free viral infectious dose that is necessary for establishment of persistent infection. In summary, this study showed that 6 year old ewes were able to efficiently transmit OPPV to lambs; however, persistent infection was not established. Future experiments will address age related antibody production and the types of antibody that may be necessary for viral clearance.
Technical Abstract: Lentiviral transmission by transfer of infected colostrum and/or milk is considered to be highly efficient. In this study, postpartum transmission of ovine progressive pneumonia virus (OPPV) from 10 naturally infected ewes to their 23 lambs was followed from the perinatal period throughout a four year period. The lambs were allowed to suckle from their dam from birth through 32 weeks of age. Virus was tracked by virus isolation, quantitative PCR (qPCR), and anti-OPPV antibody responses as measured by cELISA. Cell-associated OPPV was isolated from colostrum/milk cells in 7 out of 10 ewes and provirus envelope (env) loads ranged 8 to 106 copies/'g DNA in colostrum/milk cells from the 10 ewes using qPCR. Provirus env loads were also detected in the peripheral circulation of 21 lambs at 8 weeks and two lambs at 22 weeks. The qPCR product at 8 weeks was confirmed as the transmembrane (tm) gene of OPPV by cloning and sequencing. Both cELISA titers ranging from 325 to 3125 and cross-neutralizing antibody titers ranging from 6 to 162 to seven different OPPV strains were found in the colostrum of the 10 ewes. Furthermore, cELISA titers in serum from lambs remained detectable through 32 weeks following the clearance of provirus at 24 weeks. After 32 weeks, both provirus and anti-OPPV antibody responses have subsequently remained undetectable through 4 years of age. These data suggest the clearance of cell-associated lentiviruses from lamb circulation after passive transfer of antibody via colostrum.