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United States Department of Agriculture

Agricultural Research Service

Title: Tracking horizontal transmission of ovine lentivirus by quantitative PCR and envelope sequencing

Authors
item Neiswanger, Liam
item Hoesing, Lynn

Submitted to: Keystone Symposia
Publication Type: Abstract Only
Publication Acceptance Date: November 27, 2006
Publication Date: N/A

Interpretive Summary: Most transmission of ovine lentivirus (OvLV) occurs horizontally, but there is no direct evidence that horizontal transmission occurs from unrelated ewes to other lambs/ewes or from ewes to progeny. One way to assess the source of horizontal transmission is to evaluate OvLV strains by cloning and sequencing the envelope gene from a flock of sheep over time. One unrelated five-year old OvLV negative ewe (112-45) that had two years of previous direct contact with ten OvLV positive seven-year old ewes was placed into a flock consisting of nineteen OvLV negative three-year old ewes born from the same ten OvLV positive seven-year old ewes. After five and ten months, 112-45 and LMH35 (one of the nineteen ewes) became serologically or PCR positive, respectively. Env that was previously cloned and sequenced from colostrum cells of the original ten OvLV positive ewes was compared to env obtained from peripheral blood mononuclear cells (PBMC) of both 112-45 and LMH35 at various time points. Phylogenetic analysis revealed that env obtained from PBMC of 112-45 grouped with a clade from one the original OvLV positive ewes, LMH19; whereas env obtained from LMH35 grouped in a clade with env from OvLV positive ewe, LMH11. LMH11 is the natural mother of LMH35 suggesting that there may be a 4-year undetectable infection phase for OvLV followed by horizontal transmission via colostrum. This study shows that OvLV transmits from both unrelated ewes to ewes and from related ewes to progeny using the envelope gene as a measure of transmission. The envelope gene is highly variable in OvLV infected sheep and by examining this viral gene from different sheep, this allows tracking of viral strains.

Technical Abstract: Most transmission of ovine lentivirus (OvLV) occurs horizontally since in utero transmission is considered inefficient. However, there is no direct evidence that horizontal transmission occurs from unrelated ewes to other lambs/ewes or from ewes to progeny. One way to assess the source of horizontal transmission is to evaluate the OvLV envelope (env) gene at various time points. One unrelated five-year old OvLV negative ewe (112-45) that had two years of previous direct contact with ten OvLV positive seven-year old ewes was placed into a flock consisting of nineteen OvLV negative three-year old ewes born from the same ten OvLV positive seven-year old ewes. After five months, 112-45 seroconverted and five months later, qPCR loads were detectable at 2±0.5 copies env/ug DNA. After another five months, one ewe (LMH35) seroconverted with corresponding qPCR loads of 483±39 copies env/ug DNA. Env that was previously cloned and sequenced from colostrum cells of the original ten OvLV positive ewes was compared to env obtained from peripheral blood mononuclear cells (PBMC) of both 112-45 and LMH35 at various time points. Phylogenetic analysis revealed that env obtained from PBMC of 112-45 grouped with a clade from one the original OvLV positive ewes, LMH19; whereas env obtained from LMH35 grouped in a clade with env from OvLV positive ewe, LMH11. LMH11 is the natural mother of LMH35 suggesting that there may be a 4-year undetectable infection phase for OvLV followed by horizontal transmission via colostrum. This study shows that OvLV transmits from both unrelated ewes to ewes and from related ewes to progeny.

Last Modified: 9/21/2014
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