In vivo transcription of bovine leukemia virus and bovine immunodeficiency-like virus

Bovine leukosis virus, bovine viral diarrhea, and bovine neosporosis seroprevalence in specialized dairy herds in Antioquia-Colombia

Enzootic bovine leukosis (EBL) is a chronic infectious disease caused by the bovine leukosis virus (BLV), a Deltaretrovirus. Bovine viral diarrhea (BVD) is an infectious disease caused by a pestivirus. Bovine neosporosis is caused by the obligate intracellular parasite Neospora caninum (Nc). These pathogens can have horizontal (postnatal) or vertical (transplacental) transmissions and affect the productive and reproductive performance of infected bovines. This work aimed to detect BLV, BVD, and Nc seroprevalence in specialized dairy cattle from the north, east, and Aburrá Valley regions of the Department of Antioquia, the highest in milk production regions in Antioquia. A total of 599 blood samples, obtained from 53 specialized dairy cattle herds, were evaluated by the ELISA test. The results revealed a seroprevalence of 41.13% for BLV (242/599), 28.48% (163/599) for Nc, and 22.7% (132/599) for BVD. Regarding the regional seroprevalence evaluation, BLV was found in 47.02% of the samples from the east, 36.87% from the north, and 46.02% from the Aburrá Valley. Nc was found in 31.03% of the samples from the east, 24.26% from the north, and 36.63% from Aburrá Valley. BVD was found in 21.62% of the samples from the east, 25.03% from the north region, and 10.39% of the samples from the Aburrá Valley. It is highlighted by these results that the north region, with the highest milk production in Antioquia, had the lowest BLV and Nc seroprevalences but the highest seroprevalence of BVD. BLV has increased in Antioquia in recent years, and as an immunosuppressive infection, opportunities for other pathogens are created by it. A significant statistical difference was found in the average prevalence of the pathogens according to the municipality, cattle breed, and region of origin of the sample. The seroprevalence of these pathogens in specialized dairy herds in Antioquia can be classified as medium-low. However, it is recommended that biosecurity practices should be maximized to avoid the spread of these pathogens due to the variability detected in the region, municipality, breed group, and herd age. The rapid and efficient diagnosis of these three pathogens through reliable methodologies will allow for the control of dissemination in dairy herds.

Milk Transmission of Mammalian Retroviruses

The transmission of viruses from one host to another typically occurs through horizontal or vertical pathways. The horizontal pathways include transmission amongst individuals, usually through bodily fluids or excretions, while vertical transmission transpires from mother to their offspring, either during pregnancy, childbirth, or breastfeeding. While there are more than 200 human pathogenic viruses to date, only a small number of them are known to be transmitted via breast milk, including cytomegalovirus (CMV), human immunodeficiency virus type 1 (HIV-1), and human T cell lymphotropic virus type 1 (HTLV-1), the latter two belonging to the family Retroviridae. Breast milk transmission is a common characteristic among mammalian retroviruses, but there is a lack of reports summarizing our knowledge regarding this route of transmission of mammalian retroviruses. Here, we provide an overview of the transmission of mammalian exogenous retroviruses with a focus on Orthoretrovirinae, and we highlight whether they have been described or suspected to be transmitted through breast milk, covering various species. We also elaborate on the production and composition of breast milk and discuss potential entry sites of exogenous mammalian retroviruses during oral transmission.

Acute myelomonocytic leukemia negative for alpha-naphthyl acetate esterase stain in a Holstein cow

A 4-year, 7-month-old Holstein cow presented with anorexia. Physical examination revealed masses in the interscapular region and vagina. Blast cells were detected in the masses and peripheral blood by fine needle aspiration cytology and hematological examination. By bone marrow aspiration, blast cells constituted up to 24.2% of all nucleated cells, and 22% and 2% of non-erythroid cells stained positive for myeloperoxidase and alpha-naphthyl acetate esterase (ANAE), respectively. Pathological examination revealed the mass lesions consisted of a proliferation of tumor cells, which were positive for monocytic markers (HLA-DR and Iba-1). The cow was diagnosed with acute myelomonocytic leukemia (AMML). Even when tumor cells are ANAE-negative, AMML cannot be completely ruled out and should be considered when diagnosing cattle with leukemia/lymphoma.

A clinical case of acute myelomonocytic leukemia in a Holstein cow

A 2-year, 3-month-old Holstein cow presented with anorexia and enlarged superficial lymph nodes. Fine needle aspiration cytology of the superficial lymph nodes revealed large blast cells. Hematological examination revealed anemia, neutropenia, and blast cells in peripheral blood. Blast cells were the predominant cell type in bone marrow aspirates. Of the non-erythroid cells, 26%, 58%, and 18% were positive for myeloperoxidase, α-naphthyl acetate esterase, and naphthol AS-D chloroacetate esterase, respectively. Pathological examination revealed the proliferation of neoplastic cells, which were positive for monocytic markers, in the affected lymph nodes. The cow was diagnosed with acute myelomonocytic leukemia based on these findings. This report highlights the importance of performing bone marrow aspiration cytology and cytochemical staining when diagnosing bovine myeloid leukemia.

Current Developments in the Epidemiology and Control of Enzootic Bovine Leukosis as Caused by Bovine Leukemia Virus

Enzootic Bovine Leukosis (EBL) caused by the bovine leukemia virus (BLV) has been eradicated in over 20 countries. In contrast, the U.S. and many other nations are experiencing increasing prevalence in the absence of efforts to control transmission. Recent studies have shown that BLV infection in dairy cattle has a greater impact beyond the long-recognized lymphoma development that occurs in <5% of infected cattle. Like other retroviruses, BLV appears to cause multiple immune system disruptions, affecting both cellular and humoral immunity, which are likely responsible for increasingly documented associations with decreased dairy production and decreased productive lifespan. Realization of these economic losses has increased interest in controlling BLV using technology that was unavailable decades ago, when many nations eradicated BLV via traditional antibody testing and slaughter methods. This traditional control is not economically feasible for many nations where the average herd antibody prevalence is rapidly approaching 50%. The ELISA screening of cattle with follow-up testing via qPCR for proviral load helps prioritize the most infectious cattle for segregation or culling. The efficacy of this approach has been demonstrated in at least four herds. Breeding cattle for resistance to BLV disease progression also appears to hold promise, and several laboratories are working on BLV vaccines. There are many research priorities for a wide variety of disciplines, especially including the need to investigate the reports linking BLV and human breast cancer.

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

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.

A sensitive luminescence syncytium induction assay (LuSIA) based on a reporter plasmid containing a mutation in the glucocorticoid response element in the long terminal repeat U3 region of bovine leukemia virus

BACKGROUND

Bovine leukemia virus (BLV) causes enzootic bovine leukosis, the most common neoplastic disease of cattle. Previously, we reported the luminescence syncytium induction assay (LuSIA), an assay for BLV infectivity based on CC81-BLU3G cells, which form syncytia expressing enhanced green fluorescent protein (EGFP) when co-cultured with BLV-infected cells. To develop a more sensitive LuSIA, we here focused on the glucocorticoid response element (GRE) within the U3 region of the BLV long terminal repeat (LTR).

METHODS

We changed five nucleotide sites of the GRE in a pBLU3-EGFP reporter plasmid containing the BLV-LTR U3 region promoter by site-directed mutagenesis and we then constructed a new reporter plasmid (pBLU3_GREM-EGFP) in which the EGFP reporter gene was expressed under control of the GRE-mutated LTR-U3 promoter. We also established a new CC81-derived reporter cell line harboring the GRE-mutated LTR-U3 promoter (CC81-GREMG). To evaluate the sensibility, the utility and the specificity of the LuSIA using CC81-GREMG, we co-cultured CC81-GREMG cells with BLV-persistently infected cells, free-viruses, white blood cells (WBCs) from BLV-infected cows, and bovine immunodeficiency-like virus (BIV)- and bovine foamy virus (BFV)-infected cells.

RESULTS

We successfully constructed a new reporter plasmid harboring a mutation in the GRE and established a new reporter cell line, CC81-GREMG; this line was stably transfected with pBLU3_GREM-EGFP in which the EGFP gene is expressed under control of the GRE-mutated LTR-U3 promoter and enabled direct visualization of BLV infectivity. The new LuSIA protocol using CC81-GREMG cells measures cell-to-cell infectivity and cell-free infectivity of BLV more sensitively than previous protocol using CC81-BLU3G. Furthermore, it did not respond to BIV and BFV infections, indicating that the LuSIA based on CC81-GREMG is specific for BLV infectivity. Moreover, we confirmed the utility of a new LuSIA based on CC81-GREMG cells using white blood cells (WBCs) from BLV-infected cows. Finally, the assay was useful for assessing the activity of neutralizing antibodies in plasma collected from BLV-infected cows.

CONCLUSION

The new LuSIA protocol is quantitative and more sensitive than the previous assay based on CC81-BLU3G cells and should facilitate development of several new BLV assays.

Experimental infection of sheep with Bovine leukemia virus (BLV): Minimum dose of BLV-FLK cells and cell-free BLV and neutralization activity of natural antibodies

Bovine leukemia virus (BLV) is an important cattle pathogen that causes major economic losses worldwide, especially in dairy farms. The use of animal models provides valuable insight into the pathogenesis of viral infections. Experimental infections of sheep have been conducted using blood from BLV-infected cattle, infectious BLV molecular clones or tumor-derived cells. The Fetal Lamb Kidney cell line, persistently infected with BLV (FLK-BLV), is one of the most commonly used long-term culture available for the permanent production of virus. FLK-BLV cells or the viral particles obtained from the cell-free culture supernatant could be used as a source of provirus or virus to experimentally infect sheep. In this report, we aimed to determine the minimum amount of FLK-BLV cells or cell-free supernatant containing BLV needed to produce infection in sheep. We also evaluated the amount of antibodies obtained from a naturally-infected cow required to neutralize this infection. We observed that both sheep experimentally inoculated with 5000 FLK-BLV cells became infected, as well as one of the sheep receiving 500 FLK-BLV cells. None of the animals inoculated with 50 FLK-BLV cells showed evidence of infection. The cell-free FLK-BLV supernatant proved to be infective in sheep up to a 1:1000 dilution. Specific BLV antibodies showed neutralizing activity as none of the sheep became infected. Conversely, the animals receiving a BLV-negative serum showed signs of BLV infection. These results contribute to the optimization of a sheep bioassay which could be useful to further characterize BLV infection.

Prospects in Innate Immune Responses as Potential Control Strategies against Non-Primate Lentiviruses

Lentiviruses are infectious agents of a number of animal species, including sheep, goats, horses, monkeys, cows, and cats, in addition to humans. As in the human case, the host immune response fails to control the establishment of chronic persistent infection that finally leads to a specific disease development. Despite intensive research on the development of lentivirus vaccines, it is still not clear which immune responses can protect against infection. Viral mutations resulting in escape from T-cell or antibody-mediated responses are the basis of the immune failure to control the infection. The innate immune response provides the first line of defense against viral infections in an antigen-independent manner. Antiviral innate responses are conducted by dendritic cells, macrophages, and natural killer cells, often targeted by lentiviruses, and intrinsic antiviral mechanisms exerted by all cells. Intrinsic responses depend on the recognition of the viral pathogen-associated molecular patterns (PAMPs) by pathogen recognition receptors (PRRs), and the signaling cascades leading to an antiviral state by inducing the expression of antiviral proteins, including restriction factors. This review describes the latest advances on innate immunity related to the infection by animal lentiviruses, centered on small ruminant lentiviruses (SRLV), equine infectious anemia virus (EIAV), and feline (FIV) and bovine immunodeficiency viruses (BIV), specifically focusing on the antiviral role of the major restriction factors described thus far.

Dynamics of perinatal bovine leukemia virus infection

Background

Bovine leukemia virus (BLV) is highly endemic in many countries, including Argentina. As prevention of the spread from infected animals is of primary importance in breaking the cycle of BLV transmission, it is important to know the pathophysiology of BLV infection in young animals, as they are the main source of animal movement. In this work, we determined the proviral load and antibody titers of infected newborn calves from birth to first parturition (36 months).

Results

All calves under study were born to infected dams with high proviral load (PVL) in blood and high antibody titers and detectable provirus in the colostrum. The PVL for five out of seven calves was low at birth. All animals reached PVLs of more than 1% infected peripheral blood mononuclear cells (PBMCs), three at 3 months, one at 6 months, and one at 12 months. High PVLs persisted until the end of the study, and, in two animals, exceeded one BLV copy per cell. Two other calves maintained a high PVL from birth until the end of the study. Antibody titers were 32 or higher in the first sample from six out of seven calves. These decayed at 3–6 months to 16 or lower, and then increased again after this point.

Conclusions

Calves infected during the first week of life could play an active role in early propagation of BLV to susceptible animals, since their PVL raised up during the first 12 months and persist as high for years. Early elimination could help to prevent transmission to young susceptible animals and to their own offspring. To our knowledge, this is the first study of the kinetics of BLV proviral load and antibody titers in newborn infected calves.

Bovine immunodeficiency virus: a lentiviral infection

The bovine immunodeficiency virus (BIV) is a lentivirus which is known to infect cattle worldwide. Though serological and genomic evidence of BIV in cattle has been found throughout the world, isolation of the virus has been reported only from few places. Very little is known about its impact on animal health status, pathogenesis and mode of transmission. BIV is considered generally non-pathogenic and is not known to cause any serious disease in cattle. BIV is genetically and antigenically related to Jembrana disease virus (JDV), the cause of an acute disease in Bali cattle (Bos javanicus) and human immunodeficiency virus, the cause of acquired immunodeficiency syndrome in human. Therefore, it is important to monitor the presence of BIV in cattle to keep vigil over its possible evolution in its natural host to emerge as pathogenic lentivirus like JDV. Differentiation of BIV infection in cattle from the acutely pathogenic JDV is important for diagnosis of the latter. Currently, BIV is considered as a safe model for understanding the complex genome of lentiviruses. Further research on BIV is indeed needed to elucidate its possible role in animal health as well as for insight into the molecular mechanisms adopted by related lentiviruses.

Estimation of bovine leukemia virus (BLV) proviral load harbored by lymphocyte subpopulations in BLV-infected cattle at the subclinical stage of enzootic bovine leucosis using BLV-CoCoMo-qPCR

Background

Bovine leukemia virus (BLV) is associated with enzootic bovine leukosis (EBL), which is the most common neoplastic disease of cattle. BLV infection may remain clinically silent at the aleukemic (AL) stage, cause persistent lymphocytosis (PL), or, more rarely, B cell lymphoma. BLV has been identified in B cells, CD2⁺ T cells, CD3⁺ T cells, CD4⁺ T cells, CD8⁺ T cells, γ/δ T cells, monocytes, and granulocytes in infected cattle that do not have tumors, although the most consistently infected cell is the CD5⁺ B cell. The mechanism by which BLV causes uncontrolled CD5⁺ B cell proliferation is unknown. Recently, we developed a new quantitative real-time polymerase chain reaction (PCR) method, BLV-CoCoMo-qPCR, which enabled us to demonstrate that the proviral load correlates not only with BLV infection, as assessed by syncytium formation, but also with BLV disease progression. The present study reports the distribution of BLV provirus in peripheral blood mononuclear cell subpopulations isolated from BLV-infected cows at the subclinical stage of EBL as examined by cell sorting and BLV-CoCoMo-qPCR.

Results

Phenotypic characterization of five BLV-infected but clinically normal cattle with a proviral load of > 100 copies per 1 × 10⁵ cells identified a high percentage of CD5⁺ IgM⁺ cells (but not CD5^- IgM⁺ B cells, CD4⁺ T cells, or CD8⁺T cells). These lymphocyte subpopulations were purified from three out of five cattle by cell sorting or using magnetic beads, and the BLV proviral load was estimated using BLV-CoCoMo-qPCR. The CD5⁺ IgM⁺ B cell population in all animals harbored a higher BLV proviral load than the other cell populations. The copy number of proviruses infecting CD5^- IgM⁺ B cells, CD4⁺ cells, and CD8⁺ T cells (per 1 ml of blood) was 1/34 to 1/4, 1/22 to 1/3, and 1/31 to 1/3, respectively, compared with that in CD5⁺ IgM⁺ B cells. Moreover, the BLV provirus remained integrated into the genomic DNA of CD5⁺ IgM⁺ B cells, CD5^- IgM⁺ B cells, CD4⁺ T cells, and CD8⁺ T cells, even in BLV-infected cattle with a proviral load of <100 copies per 10⁵ cells.

Conclusions

The results of the recent study showed that, although CD5⁺ IgM⁺ B cells were the main cell type targeted in BLV-infected but clinically normal cattle, CD5^- IgM⁺ B cells, CD4⁺ cells, and CD8⁺ T cells were infected to a greater extent than previously thought.

Prior bovine immunodeficiency virus infection does not inhibit subsequent superinfection by the acutely pathogenic Jembrana disease virus

In cattle the interaction between the two genetically and antigenically related bovine lentiviruses, the acutely pathogenic Jembrana disease virus (JDV) and the non-pathogenic Bovine immunodeficiency virus (BIV) has not been reported although both JDV and a BIV-like virus have been reported in the Bali cattle (Bos javanicus) population in Indonesia. The outcome of infection of Bali cattle with the R29 strain of BIV prior to superinfection 42 days later with JDV(TAB/87) was determined. All BIV-inoculated cattle were successfully infected and developed an antibody response to the TM and CA proteins. BIV infection did not prevent subsequent infection with JDV or ameliorate the clinical signs of Jembrana disease in the infected cattle. It did, however, modify the dynamics of the JDV infection with an earlier onset and end of the acute disease process, and a reduction in the duration of viremia that exceeded 10(6) genome copies/ml of plasma.

Bovine immunodeficiency virus produces a transient viraemic phase soon after infection in Bos javanicus

Infection of Bali cattle (Bos javanicus) in Indonesia with a non-pathogenic bovine lentivirus similar to Bovine immunodeficiency virus (BIV) is suspected but efforts to detect the virus have been unsuccessful. To define the kinetics of BIV infection in Bali cattle, 13 were infected with the R-29 strain of BIV and monitored for 60 days. No clinical effects were detected. Proviral DNA was detected in peripheral blood mononuclear cells from 4 to 60 days with peak titres 20 days post-infection (dpi). There was a transient viraemia from 4 to 14 dpi with a maximum titre of 1x10(4)genome copies/ml plasma. An antibody response to the transmembrane (TM) glycoprotein commenced 12 dpi but an antibody response to the capsid (CA) protein was detected in one animal only and not until 34 dpi. The results indicated that detection of BIV in infected Bali cattle would have a greater chance of success soon after infection and prior to the onset of a CA antibody response.

Mechanisms of leukemogenesis induced by bovine leukemia virus: prospects for novel anti-retroviral therapies in human

In 1871, the observation of yellowish nodules in the enlarged spleen of a cow was considered to be the first reported case of bovine leukemia. The etiological agent of this lymphoproliferative disease, bovine leukemia virus (BLV), belongs to the deltaretrovirus genus which also includes the related human T-lymphotropic virus type 1 (HTLV-1). This review summarizes current knowledge of this viral system, which is important as a model for leukemogenesis. Recently, the BLV model has also cast light onto novel prospects for therapies of HTLV induced diseases, for which no satisfactory treatment exists so far.