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Detection of Bovine Leukemia Virus RNA in Blood Samples of Naturally Infected Dairy Cattle.

ABSTRACT: The viral expression in vivo, in bovine leukemia virus (BLV)-infected cattle, is considered to be restricted to extremely low levels, and the mitosis of infected B lymphocytes is regarded as the main mode of virus persistence within the infected host. In this study, the presence of BLV RNA in whole blood from seven asymptomatic cows naturally infected with BLV during one year, including a complete milking cycle and two delivery time points, was investigated by nested-PCR using the oligonucleotides complementary to the tax and pol gene. BLV RNA was detected in four cows at different time points, especially in high blood proviral load cows and around delivery time. This study describes for the first time the detection of free BLV RNA in blood from BLV-infected asymptomatic cows. The results obtained suggest the occurrence of persistent low-level expression of the tax and pol genes that could be a result of viral reactivation, within the asymptomatic period. This finding may be important in the pathogenesis of BLV infection, associated with the delivery period.

SUBMITTER: Alvarez I

PROVIDER: S-EPMC6789540 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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Detection of Bovine Leukemia Virus RNA in Blood Samples of Naturally Infected Dairy Cattle.

Alvarez Irene I Porta Natalia Gabriela NG Trono Karina K

Veterinary sciences 20190806 3

The viral expression in vivo, in bovine leukemia virus (BLV)-infected cattle, is considered to be restricted to extremely low levels, and the mitosis of infected B lymphocytes is regarded as the main mode of virus persistence within the infected host. In this study, the presence of BLV RNA in whole blood from seven asymptomatic cows naturally infected with BLV during one year, including a complete milking cycle and two delivery time points, was investigated by nested-PCR using the oligonucleotid ...[more]

PMID: 31390719

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Project description:Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis (EBL), a disease that has worldwide distribution. Whilst it has been eradicated in most of Western Europe and Scandinavia, it remains a problem in other regions, particularly Eastern Europe and South America. For this study, in 2013, 24 cattle from three farms in three regions of Moldova were screened by ELISA and nested PCR. Of these cattle, 14 which were PCR positive, and these were molecularly characterized based on the nucleotide sequence of the env gene and the deduced amino acid sequence of the encoded gp51 protein. Our results demonstrated a low level of genetic variability (0-2.9%) among BLV field strains from Moldova, in contrast to that observed for other retroviruses, including human immunodeficiency virus (HIV) (20-38%) Mason IL (Trudy vologod moloch Inst 146-164, 1970) and equine infectious anemia virus (EIAV) (~40%) Willems L et al (AIDS Res Hum Retroviruses 16(16):1787-1795, 2000), where the envelope gene exhibits high levels of variation Polat M et al (Retrovirology 13(1):4, 2016). Sequence comparisons and phylogenetic analysis revealed that BLV genotype 7 (G7) is predominant in Moldova and that the BLV population in Moldovan cattle is a mixture of at least three new sub-genotypes: G7D, G7E and G4C. Neutrality tests revealed that negative selection was the major force operating upon the 51-kDa BLV envelope surface glycoprotein subunit gp51, although one positively selected site within conformational epitope G was detected in the N-terminal part of gp51. Furthermore, two functional domains, linear epitope B and the zinc-binding domain, were found to have an elevated ratio of nonsynonymous to synonymous codon differences. Together, these data suggest that the evolutionary constraints on epitopes G and B and the zinc-binding domains of gp51 differ from those on the other domains, with a tendency towards formation of homogenous genetic groups, which is a common concept of global BLV diversification during virus transmission that may be associated with genetic drift.

Project description:BackgroundThe absence of virus expression during the chronic stage of bovine leukemia virus (BLV) infection and its reactivation upon ex vivo culture has become a long-lived Dogma. During the chronic stage of BLV infection the immune response limits viral replication and the mitotic division of latently infected cells, carrying BLV provirus, allows viral expansion and disease progression towards a lymphoproliferative disorder. Several stressor factors have been associated with animal production and handling. As natural mediator of stress, glucocorticoids are strong immunosuppressive agents; moreover, they can bind long-terminal repeat region of retroviruses and induce viral expression. In the present study, we present a case report describing the spontaneous reactivation of BLV infection in naturally infected cattle.Case presentationIn order to investigate if virus reactivation occurred in vivo during the course of BLV infection, we followed up for 328 days one Holstein cow (> 3 years) chronically infected with BLV which presented high-proviral loads. This animal was neither lactating nor pregnant. Furthermore, we investigated if a stressor stimulus, in this case the administration of a synthetic glucocorticoid (dexamethasone), could impact the course of BLV infection in three additional cattle. For the first time, we observed a high level of BLV transcripts in a total of four cattle chronically infected with BLV. The detection of viral transcripts corresponding to pol gene strongly suggests virus reactivation in these animals. Interestingly, this simultaneous virus reactivation was unrelated to dexamethasone treatment.ConclusionsWe reported for the first time spontaneous and high level of BLV transcriptional activation in cattle chronically infected with BLV. Although virus reactivation was unrelated to dexamethasone treatment, other stressor stimuli might have influenced this outcome. Future studies will be necessary to understand these observations, since the spontaneous virus reactivation presented here might have implications on BLV pathogenesis and transmission.

Dataset Information

Detection of Bovine Leukemia Virus RNA in Blood Samples of Naturally Infected Dairy Cattle.

Publications

Detection of Bovine Leukemia Virus RNA in Blood Samples of Naturally Infected Dairy Cattle.

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