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Title: Non-maternal transmission is the major mode of ovine lentivirus transmission in a ewe flock: A molecular epidemiology study

item BROUGHTON-NEISWANGER, LIAM - Washington State University
item White, Stephen
item Knowles Jr, Donald
item Mousel, Michelle
item Lewis, Gregory
item Herndon, David
item Hoesing, Lynn

Submitted to: Infection, Genetics and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2010
Publication Date: 10/1/2010
Citation: 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.

Interpretive Summary: Ovine progressive pneumonia virus (OPPV) is a persistent lentivirus causing a slow, progressive disease in ewes resulting in insidious losses to the sheep producer. Elucidating the major routes of OPPV transmission is key to eradication and vaccine design. It is unknown whether maternal or horizontonal transmission of OPPV contributes more to overall transmission. Using DNA analyses of viral sequences in OPPV infected dam-daughter pairs of an Idaho ewe flock, it was determined that maternal transmission contributes 10-14.3% while horizontal transmission contributes 85.7-90% to overall transmission. These data indicate that maternal transmission which includes in utero, antepartum, and post parturition (contact and colostrum/milk) routes is a minor component of overall transmission of this particular ewe flock. The rate of evolution of OPPV within an animal was also determined and comparable to rates of evolution in other lentiviruses such as human immunodeficiency virus. Future studies are planned to evaluate different routes of horizontal transmission for their contribution to overall transmission.

Technical Abstract: Transmission of ovine progressive pneumonia virus (OPPV), a lentivirus of sheep, occurs through both maternal and non-maternal means. Currently, the contribution of each route to the overall flock OPPV prevalence is poorly understood since previous serological epidemiologic studies lacked the ability to accurately track routes of transmission within an infected flock. In this study, the amount of maternal OPP transmission was assessed in a naturally infected ewe flock by applying molecular analyses to proviral sequences derived from peripheral blood leukocytes of OPP positive dam-daughter pairs (N=40). Both proviral envelope (env) and long terminal repeat (ltr) sequences, separately and combined, were utilized in the following two sequence analysis methods: phylogenetic analysis and pairwise distance calculations. True maternal transmission events were defined as agreement in 2 out of the 2 sequence analysis methods. Using this criterion, proviral env sequences resulted in a 14.3% maternal transmission frequency, and proviral ltr sequences resulted in a 10% maternal transmission frequency. Both proportions of maternal transmission varied significantly from equality (P <0.0001). This indicates that the remaining 85.7-90% of daughters are infected via non-maternal transmission. This is also the first study to calculate the OPP proviral rate of change for env and ltr genes. Accurately defining the routes of OPPV transmission provides critical epidemiological data supporting management intended to reduce flock transmission and viral dose.