Risk factors associated with within-herd transmission of bovine leukemia virus on dairy farms in Japan

Analysis of factors associated with the first lumpy skin disease outbreaks in naïve cattle herds in different regions of Thailand

Introduction

Thailand experienced a nationwide outbreak of lumpy skin disease (LSD) in 2021, highlighting the need for effective prevention and control strategies. This study aimed to identify herd-level risk factors associated with LSD outbreaks in beef cattle herds across different regions of Thailand.

Methods

A case-control study was conducted in upper northeastern, northeastern, and central regions, where face-to-face interviews were conducted with farmers using a semi-structured questionnaire. Univariable and multivariable mixed effect logistic regression analyses were employed to determine the factors associated with LSD outbreaks. A total of 489 beef herds, including 161 LSD outbreak herds and 328 non-LSD herds, were investigated.

Results and discussion

Results showed that 66% of farmers have operated beef herds for more than five years. There were very few animal movements during the outbreak period. None of the cattle had been vaccinated with LSD vaccines. Insects that have the potential to act as vectors for LSD were observed in all herds. Thirty-four percent of farmers have implemented insect control measures. The final mixed effect logistic regression model identified herds operating for more than five years (odds ratio [OR]: 1.62, 95% confidence interval [CI]: 1.04-2.53) and the absence of insect control management on the herd (OR: 2.05, 95% CI: 1.29-3.25) to be associated with LSD outbreaks. The implementation of insect-vector control measures in areas at risk of LSD, especially for herds without vaccination against the disease, should be emphasized. This study provides the first report on risk factors for LSD outbreaks in naïve cattle herds in Thailand and offers useful information for the development of LSD prevention and control programs within the country's context.

The influence of risk factors on bovine leukemia virus infection and proviral load in egyptian cattle

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leucosis (EBL), which affects cattle globally. In Egypt, BLV control strategies have been ignored because of the shortage of BLV research studies and the silent infection in most animals. This study aimed to identify the risk factors associated with the prevalence of BLV among dairy and beef cattle from six different geographic and climatic provinces in Egypt. Additionally, risk factors affecting the BLV proviral load (PVL) among the positive cattle were targeted. The total BLV prevalence in cattle from six investigated Egyptian provinces was 24.2% (105/433), while the mean PVL (8651.6 copies /105 white blood cells) was absolutely high as estimated by the BLV-CoCoMo-quantitative polymerase chain reaction (qPCR)-2 assay. Analysis of the influence of risk factors (age, sex, breed, production type, farm size, and location) on BLV prevalence indicated that the Holstein breed (OR = 1.582, p = 0.007), beef cattle (OR = 1.088, p = 0.0001), large-size farms (OR = 1.26, p = 0.0001), and cattle from Damietta (OR = 1.43, p = 0.0001) and Cairo (OR = 1.16, p = 0.0001) were ultimately proven the most important risks for BLV infection. The risk factors were analyzed considering the BLV PVL levels in the BLV-positive cases. Significantly high PVL (HPVL) levels were observed in cattle > 5 years old (p < 0.0001), females (p = 0.0008), Holstein (p < 0.0001), dairy cows (p = 0.0053), large-size farms (p < 0.0001), and cattle from Damietta (p < 0.0001) compared to other categories. Contrary, no significant differences in PVL levels were reported between the Native and Mixed cattle breeds (p = 0.13). Ultimately, the logistic regression model indicated that the probability of carrying HPVL in cattle > 5 years is 1.27 (95% CI: 1.03-2.09, p < 0.001) times more likely compared to cattle < 2 years old. In conclusion, the findings were valuably correlating the BLV prevalence with PVL as an indicator of the risk of BLV infection.

BoLA-DRB3 Polymorphism Associated with Bovine Leukemia Virus Infection and Proviral Load in Holstein Cattle in Egypt

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis, the most prevalent neoplastic disease of cattle worldwide. The immune response to BLV and disease susceptibility and resistance in cattle are strongly correlated with the bovine leukocyte antigen (BoLA)-DRB3 allelic polymorphism. BLV infection continues to spread in Egypt, in part because the relationships between BLV infection, proviral load in Egypt, and BoLA-DRB3 polymorphism are unknown. Here, we identified 18 previously reported alleles in 121 Holstein cows using a polymerase chain reaction sequence-based typing method. Furthermore, BoLA-DRB3 gene polymorphisms in these animals were investigated for their influence on viral infection. BoLA-DRB3*015:01 and BoLA-DRB3*010:01 were identified as susceptible and resistant alleles, respectively, for BLV infection in the tested Holsteins. In addition, BoLA-DRB3*012:01 was associated with low PVL in previous reports but high PVL in Holstein cattle in Egypt. This study is the first to demonstrate that the BoLA-DRB3 polymorphism confers resistance and susceptibility to PVL and infections of BLV in Holstein cattle in Egypt. Our results can be useful for the disease control and eradication of BLV through genetic selection.

Seroprevalence and risk factors associated with bovine Leukemia virus infection in argentine beef cattle

Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis, an endemic disease in dairy cattle of Argentina. However, little is known about the seroprevalence of BLV in beef cattle. In this study, we conducted a cross-sectional study including farms from thirteen provinces of Argentina. A total of 5827 bovine serum samples were collected from 76 farms and analyzed using an in-house developed enzyme-linked immunosorbent assay. Information about herd management was collected through a questionnaire, and univariate and multivariate analyses were performed to detect risk factors associated with BLV infection. Herd-level seroprevalence was 71.05%, while the mean animal-level seroprevalence was 7.23% (median = 2.69%; min = 0, max = 75). Only two provinces had no positive BLV samples. The other eleven provinces showed more than 50% of their farms infected with BLV. The multivariate model revealed that BLV prevalence was significantly associated with the use of animals raised in the same farm for cattle replacement (P = 0.005), breeding cows by natural mating with a bull (P < 0.001), and weaning calves after 6 months of age (P = 0.011). This extensive study revealed that BLV seroprevalence in Argentine beef farms has increased during the last years and allowed identifying some management practices associated with BLV prevalence. These data deserve special attention because BLV infection in beef cattle seems to lead to a dissemination pattern similar to that observed during the last decades in dairy cattle, especially considering that Argentina is the sixth beef producer in the world, with about 5% of global beef production.

Seroprevalence and haemato-biochemical effects of bovine leucosis in buffalo, Punjab, Pakistan

Enzootic bovine leucosis is caused by bovine leukaemia virus (BLV), a Deltaretrovirus belonging to the family Retroviridae. BLV causes huge economic losses to the dairy industry in the form of decreased milk production, premature culling, and poor reproductive performance of the animals. The aim of the present study was to determine the seroprevalence of BLV infection in buffalo in two districts of Punjab, Pakistan. A total of 384 samples were collected and analysed using a commercial indirect enzyme-linked immunosorbent assay (ELISA) to investigate the seroprevalence of BLV through the detection of the anti-BLV gp51 antibody. A predesigned data questionnaire proforma was employed to find out the association of risk factors with disease. Overall, 18.2% of buffaloes were seropositive for BLV in the study population. The results revealed a significant association (P < 0.05) of age with BLV infection. Furthermore, milk yield and pregnancy had a significant association with the seroprevalence of BLV infection in buffalo whereas no significant association was found with sex, breeding, and health status. Biochemical and oxidative stress markers revealed a significant decrease in liver enzymes alanine transaminase (ALT) and aspartate transaminase (AST), glutathione peroxidase (GPX), and superoxide dismutase (SOD) in seropositive animals as compared to healthy animals. It is concluded that BLV has a considerable prevalence in buffalo in Punjab, Pakistan and there is a dire need to investigate the disease epidemiology at both national and international levels and strategies should be developed to implement an effective control program.

Application of the Luminescence Syncytium Induction Assay to Identify Chemical Compounds That Inhibit Bovine Leukemia Virus Replication

Bovine leukemia virus (BLV) infection causes endemic bovine leukemia and lymphoma, resulting in lower carcass weight and reduced milk production by the infected cattle, leading to economic losses. Without effective measures for treatment and prevention, high rates of BLV infection can cause problems worldwide. BLV research is limited by the lack of a model system to assay infection. To overcome this, we previously developed the luminescence syncytium induction assay (LuSIA), a highly sensitive and objectively quantifiable method for visualizing BLV infectivity. In this study, we applied LuSIA for the high-throughput screening of drugs that could inhibit BLV infection. We screened 625 compounds from a chemical library using LuSIA and identified two that markedly inhibited BLV replication. We then tested the chemical derivatives of those two compounds and identified BSI-625 and -679 as potent inhibitors of BLV replication with low cytotoxicity. Interestingly, BSI-625 and -679 appeared to inhibit different steps of the BLV lifecycle. Thus, LuSIA was applied to successfully identify inhibitors of BLV replication and may be useful for the development of anti-BLV drugs.

Endemicity of Coxiella burnetii infection among people and their livestock in pastoral communities in northern Kenya

Background

Coxiella burnetti can be transmitted to humans primarily through inhaling contaminated droplets released from infected animals or consumption of contaminated dairy products. Despite its zoonotic nature and the close association pastoralist communities have with their livestock, studies reporting simultaneous assessment of C. burnetti exposure and risk-factors among people and their livestock are scarce.

Objective

This study therefore estimated the seroprevalence of Q-fever and associated risk factors of exposure in people and their livestock.

Materials and methods

We conducted a cross-sectional study in pastoralist communities in Marsabit County in northern Kenya. A total of 1,074 women and 225 children were enrolled and provided blood samples for Q-fever testing. Additionally, 1,876 goats, 322 sheep and 189 camels from the same households were sampled. A structured questionnaire was administered to collect individual- and household/herd-level data. Indirect IgG ELISA kits were used to test the samples.

Results

Household-level seropositivity was 13.2% [95% CI: 11.2–15.3]; differences in seropositivity levels among women and children were statistically insignificant (p = 0.8531). Lactating women had higher odds of exposure, odds ratio (OR) = 2.4 [1.3–5.3], while the odds of exposure among children increased with age OR = 1.1 [1.0–1.1]. Herd-level seroprevalence was 83.7% [81.7–85.6]. Seropositivity among goats was 74.7% [72.7–76.7], while that among sheep and camels was 56.8% [51.2–62.3] and 38.6% [31.6–45.9], respectively. Goats and sheep had a higher risk of exposure OR = 5.4 [3.7–7.3] and 2.6 [1.8–3.4], respectively relative to camels. There was no statistically significant association between Q-fever seropositivity and nutrition status in women, p = 0.900 and children, p = 1.000. We found no significant association between exposure in people and their livestock at household level (p = 0.724) despite high animal exposure levels, suggesting that Q-fever exposure in humans may be occurring at a scale larger than households.

Conclusion

The one health approach used in this study revealed that Q-fever is endemic in this setting. Longitudinal studies of Q-fever burden and risk factors simultaneously assessed in human and animal populations as well as the socioeconomic impacts of the disease and further explore the role of environmental factors in Q-fever epidemiology are required. Such evidence may form the basis for designing Q-fever prevention and control strategies.

Identification of BoLA Alleles Associated with BLV Proviral Load in US Beef Cows

Bovine leukemia virus (BLV) causes enzootic bovine leukosis, the most common neoplastic disease in cattle. Previous work estimates that 78% of US beef operations and 38% of US beef cattle are seropositive for BLV. Infection by BLV in a herd is an economic concern for producers as evidence suggests that it causes an increase in cost and a subsequent decrease in profit to producers. Studies investigating BLV in dairy cattle have noted disease resistance or susceptibility, measured by a proviral load (PVL) associated with specific alleles of the bovine leukocyte antigen (BoLA) DRB3 gene. This study aims to investigate the associations between BoLA DRB3 alleles and BLV PVL in beef cattle. Samples were collected from 157 Midwest beef cows. BoLA DRB3 alleles were identified and compared with BLV PVL. One BoLA DRB3 allele, *026:01, was found to be associated with high PVL in relation to the average of the sampled population. In contrast, two alleles, *033:01 and *002:01, were found to be associated with low PVL. This study provides evidence of a relationship between BoLA DRB3 alleles and BLV PVL in US beef cows.

Dairy Cows Experimentally Infected With Bovine Leukemia Virus Showed an Increased Milk Production in Lactation Numbers 3–4: A 4-Year Longitudinal Study

Bovine leukemia virus (BLV) is widespread in global cattle populations, but the effects of its infection on milk quantity and quality have not been clearly elucidated in animal models. In this study, 30 healthy first-lactation cows were selected from ≈2,988 cows in a BLV-free farm with the same criteria of parity, age, lactation number, as well as milk yield, SCS, and composition (fat, protein, and lactose). Subsequently, these cows were randomly assigned to the intervention (n = 15) or control (n = 15) group, and reared in different cowsheds. Cows in the intervention group were inoculated with 1 × phosphate-buffered solution (PBS) resuspended in peripheral blood mononuclear cells (PBMC) from a BLV-positive cow, while the controls were inoculated with the inactivated PBMC from the same individual. From June 2016 to July 2021, milk weight (kg) was automatically recorded by milk sensors, and milk SCS and composition were originated from monthly performed dairy herd improvement (DHI) testing. Fluorescence resonance energy transfer (FRET)–qPCR and ELISA showed that cows in the intervention group were successfully infected with BLV, while cows in the control group were free of BLV for the entire period. At 45 days post-inoculation (DPI), the numbers of whole blood cells (WBCs) (P = 0.010), lymphocytes (LYMs) (P = 0.002), and monocytes (MNCs) (P = 0.001) and the expression levels of IFN-γ (P = 0.013), IL-10 (P = 0.031), and IL-12p70 (P = 0.008) increased significantly in the BLV infected cows compared to the non-infected. In lactation numbers 2–4, the intervention group had significantly higher overall milk yield (P < 0.001), fat (P = 0.031), and protein (P = 0.050) than the control group, while milk SCS (P = 0.038) and lactose (P = 0.036) decreased significantly. Further analysis indicated that BLV infection was associated with increased milk yield at each lactation stage in lactation numbers 3–4 (P = 0.021 or P < 0.001), but not with SCS and milk composition. Together, this 4-year longitudinal study revealed that artificial inoculation of BLV increased the milk yield in cows in this BLV challenge model.

Molecular Characterization of Bovine Leukemia Virus with the Evidence of a New Genotype Circulating in Cattle from Kazakhstan

Bovine leukemia virus (BLV) is a retrovirus that causes enzootic bovine leukosis (EBL) and has worldwide distribution. Infections with BLV have been reported in cattle from Kazakhstan but the virus has not yet been thoroughly characterized. In this study, we detect and estimate the level of BLV proviral DNA by qPCR in DNA samples from 119 cattle naturally infected with BLV, from 18 farms located in four different geographical regions of Kazakhstan. Furthermore, we conducted the phylogenetic and molecular analysis of 41 BLV env-gp51 gene sequences from BLV infected cattle. Phylogenetic analysis showed the affiliation of sequences to two already known genotypes G4 and G7 and also to a new genotype, classified as genotype G12. In addition, a multivariate method was employed for analysis of the association between proviral load and different variables such as the geographical location of the herd, cattle breeds, age of animals, and the presence of particular BLV genotypes. In summary, the results of this study provide the first evidence on molecular characterization of BLV circulating in cattle from Kazakhstan.

Potential Risk Factors Associated with Infection with Bovine Leukaemia Virus in Dairy and Beef Cattle in Taiwan

Bovine leukaemia virus (BLV), which is classified as a Deltaretrovirus, is the aetiologic agent of enzootic bovine leukosis (EBL), a chronic lymphoproliferative disorder with a worldwide distribution. EBL is widespread in dairy herds and causes a direct economic impact due to reduced milk production and the early culling of BLV-infected cattle. The BLV infection status in Taiwan remains largely unknown; a high prevalence of BLV in dairy cows was recently revealed. The present study further investigated BLV infections in beef cattle. Surprisingly, the prevalence of BLV proviral DNA was as low as 11.8% (23/195), which is significantly lower than that noted in dairy cows, which was 42.5% (102/240) (p < 0.001). Factors associated with BLV infections were subsequently investigated. Due to the differences in herd management, an analysis of risk factors for a BLV infection was independently conducted in these two sectors. Several factors associated with a BLV infection were identified. Age was significantly associated with BLV infection status in dairy cows (p < 0.001) but not in beef cattle. A high prevalence of BLV was observed in cattle >15.5 months old (57.8%) compared with those ≤15.5 months old (11.4%). Moreover, after stratification analysis, based on the critical age of 15.5 months, as determined by the receiver operating characteristic (ROC) curve, a significantly higher BLV prevalence was demonstrated in lactating dairy cows, cattle undergoing bull breeding, heifers at older ages, and those undergoing routine rectal palpation. Due to the high prevalence of BLV in Taiwan, the development of an effective control program, based on the identified risk factors, is important for interrupting the routes of BLV transmission within herds.

A pooled testing system to rapidly identify cattle carrying the elite controller BoLA-DRB3*009:02 haplotype against bovine leukemia virus infection

As genetically resistant individuals, the “elite controllers” (ECs) of human immunodeficiency virus infection have been focused on as the keys to developing further functional treatments in medicine. In the livestock production field, identifying the ECs of bovine leukemia virus (BLV) infection in cattle is desired to stop BLV transmission chains on farms. Cattle carrying the bovine leukocyte antigen (BoLA)‐DRB3*009:02 allele (DRB3*009:02) have a strong possibility of being BLV ECs. Most of cattle carrying this allele maintain undetectable BLV proviral loads and do not shed virus even when infected. BLV ECs can act as transmission barriers when placed between uninfected and infected cattle in a barn. To identify cattle carrying DRB3*009:02 in large populations more easily, we developed a pooled testing system. It employs a highly sensitive, specific real‐time PCR assay and TaqMan MGB probes (DRB3*009:02‐TaqMan assay). Using this system, we determined the percentage of DRB3*009:02‐carrying cattle on Kyushu Island, Japan. Our pooled testing system detected cattle carrying the DRB3*009:02 allele from a DNA pool containing one DRB3*009:02‐positive animal and 29 cattle with other alleles. Its capacity is sufficient for herd‐level screening for DRB3*009:02‐carrying cattle. The DRB3*009:02‐TaqMan assay showed high‐discriminative sensitivity and specificity toward DRB3*009:02, making it suitable for identifying DRB3*009:02‐carrying cattle in post‐screening tests on individuals. We determined that the percentage of DRB3*009:02‐carrying cattle in Kyushu Island was 10.56%. With its ease of use and reliable detection, this new method strengthens the laboratory typing for DRB3*009:02‐carrying cattle. Thus, our findings support the use of BLV ECs in the field.

Bovine Leukaemia Virus: Current Epidemiological Circumstance and Future Prospective

Bovine leukaemia virus (BLV) is a deltaretrovirus that is closely related to human T-cell leukaemia virus types 1 and 2 (HTLV-1 and -2). It causes enzootic bovine leukosis (EBL), which is the most important neoplastic disease in cattle. Most BLV-infected cattle are asymptomatic, which potentiates extremely high shedding rates of the virus in many cattle populations. Approximately 30% of them show persistent lymphocytosis that has various clinical outcomes; only a small proportion of animals (less than 5%) exhibit signs of EBL. BLV causes major economic losses in the cattle industry, especially in dairy farms. Direct costs are due to a decrease in animal productivity and in cow longevity; indirect costs are caused by restrictions that are placed on the import of animals and animal products from infected areas. Most European regions have implemented an efficient eradication programme, yet BLV prevalence remains high worldwide. Control of the disease is not feasible because there is no effective vaccine against it. Therefore, detection and early diagnosis of the disease are essential in order to diminish its spreading and the economic losses it causes. This review comprises an overview of bovine leukosis, which highlights the epidemiology of the disease, diagnostic tests that are used and effective control strategies.

Absence of bovine leukemia virus in the buffy coats of breast cancer cases from Alabama, USA

Breast cancer is reported as one of the most common and deadly cancers among females. Recent findings have suggested that bovine leukemia virus (BLV), a highly prevalent bovine virus worldwide, might be linked to human breast cancer. However, the involvement of BLV as a risk factor for breast cancer remains controversial. In this study, BLV FRET-PCR was carried out on 238 blood-derived DNA samples from breast cancer patients from the Alabama Hereditary Cancer Cohort. In addition, randomly selected samples (n = 20) were evaluated by WGS for the presence of BLV genome. No BLV proviral DNA was detected in any of 238 samples assayed by FRET-qPCR in this study. Similarly, the WGS analysis did not detect the presence of the BLV genome in the DNA of the buffy coats from 20 randomly selected patients with breast cancer. This study did not support the findings of suggesting an association between BLV and breast cancer. Notably, nearly all the studies using in situ PCR and immunohistochemistry demonstrated positive associations while other studies using whole-genome sequencing and other methods failed to identify the BLV association with breast cancer. Further studies including all reported BLV detection techniques/methods on the same breast cancer sample sets would appear to be the most likely way of resolving the current contradictory evidence.

Review on bovine respiratory syncytial virus and bovine parainfluenza - usual suspects in bovine respiratory disease - a narrative review

Bovine Respiratory Syncytial virus (BRSV) and Bovine Parainfluenza 3 virus (BPIV3) are closely related viruses involved in and both important pathogens within bovine respiratory disease (BRD), a major cause of morbidity with economic losses in cattle populations around the world. The two viruses share characteristics such as morphology and replication strategy with each other and with their counterparts in humans, HRSV and HPIV3. Therefore, BRSV and BPIV3 infections in cattle are considered useful animal models for HRSV and HPIV3 infections in humans.

The interaction between the viruses and the different branches of the host’s immune system is rather complex. Neutralizing antibodies seem to be a correlate of protection against severe disease, and cell-mediated immunity is thought to be essential for virus clearance following acute infection. On the other hand, the host’s immune response considerably contributes to the tissue damage in the upper respiratory tract.

BRSV and BPIV3 also have similar pathobiological and epidemiological features. Therefore, combination vaccines against both viruses are very common and a variety of traditional live attenuated and inactivated BRSV and BPIV3 vaccines are commercially available.

Bayesian Estimation of the True Seroprevalence and Risk Factor Analysis of Bovine Leukemia Virus Infection in Pakistan

Simple Summary

The enzootic bovine leucosis is the most common and economically important viral disease of cattle, caused by bovine leukemia virus (BLV). In cattle, infection with BLV leads to decreased milk production and premature culling and also impairs the immune system predisposing animals to other infections and increasing severity of disease. The aim of this study was to estimate the true seropositivity to BLV at the farm and within-farm levels in Pakistan, using a latent class analysis. In addition, some factors influencing BLV seropositivity were analyzed. We tested 1380 dairy cattle from 451 herds and 92 water buffalo. Analysis at the within-herd and herd levels showed 3.8% of cattle and 1.4% of herds were truly seropositive. All 92 serum samples from water buffalo were negative. The study demonstrated strong association between BLV seroprevalence and herd size but not with common housing of cattle representing indigenous breeds with exotic breed or their crossbred and also common housing of cattle and water buffalo.

Abstract

The objective of this study was to determine the true seroprevalence of bovine leukemia virus (BLV) infection in dairy cattle from Pakistan at the animal and herd-level. We tested 1380 dairy cattle from 451 herds and 92 water buffalo. The sera were tested by ELISA and the results were analyzed using Bayesian inference. The median posterior estimate of the herd level true BLV prevalence was 1.4%, with a 95% credible interval (CI) 0.7–3.1, whereas the median posterior estimate of the within-farm true seroprevalence was 3.8% with a 95% CI 2.8–4.8. All 92 sera collected from water buffalo were negative. Several risk factors potentially associated with seropositivity to BLV infections in Pakistan were analyzed using logistic regression model based on calculation of an odds ratio (OR). The study showed an association between seropositivity and medium herd (≥50) size (OR = 23.57, 95% CI: 3.01–103.48). Common housing of indigenous cattle with exotic-breed cattle (OR = 0.67, 95% CI: 06–2.35) or housing indigenous or their crossbred cattle with exotic-breed cattle (OR = 0.95, 95% CI: 0.14–3.01) had no effect on the BLV seroprevalence. Similarly, common housing of cattle and water buffalo was not risk factor for increased BLV seropositivity (OR = 27.10, 95% CI: 0.63–119.34).

Invited review: Bovine leukemia virus-Transmission, control, and eradication

Bovine leukemia virus (BLV) infection, endemic in North American dairy herds, has production-limiting effects. A literature review of available papers published since 1995 concerning BLV transmission and its control was conducted. Although confirmed transmission routes were reviewed (blood, natural breeding, in utero, colostrum, and milk), there is still a lack of detailed information on other specific risks for transmission (e.g., contact transmission and hoof-trimming knives). Eradication of BLV has been achieved by combined management, segregation, and culling approaches. In contrast, although sole implementation of best management practices aimed at prevention of BLV transmission has decreased within-herd BLV prevalence, it has not eradicated BLV from a herd. Therefore, control and eradication of BLV by best management practices only should be further investigated. Additionally, the role of proviral load in infected cattle was investigated. Cattle with a high proviral load seem to be more likely to infect others, whereas those with a very low proviral load seem to have low risks of transmitting BLV. Information on proviral load could be taken into account when controlling BLV in high-prevalence herds. In conclusion, there is a need for detailed, large-scale studies investigating roles of specific transmission routes, knowing proviral load of infected individuals.

Effectiveness of on-farm continuous flow high-temperature short-time pasteurization for inactivation of bovine leukemia virus in milk

The effectiveness of on-farm continuous flow high-temperature short-time (HTST) pasteurization (i.e., 72°C for 15 s) for the inactivation of bovine leukemia virus (BLV) in milk was investigated with a sheep bioassay. Four sheep that had been inoculated with completely pasteurized milk containing approximately 3.4 × 10⁷ BLV-infected peripheral blood mononuclear cells (PBMC) and treated by either HTST pasteurization or laboratory-scale low-temperature long-time (LTLT) pasteurization (i.e., 60°C for 30 min), remained negative for BLV for at least 17 weeks after inoculation. In contrast, all sheep inoculated with unpasteurized or inadequately pasteurized milk containing the same number of BLV-infected PBMC were tested positive for BLV and anti-BLV antibodies within 3 weeks after inoculation. These results suggest that on-farm continuous flow HTST pasteurization was equivalent value with inactivated BLV on the LTLT procedure and can effectively inactivate BLV in the milk. Therefore, on-farm HTST pasteurization of the pooled colostrum or milk used in automated feeding systems is likely to protect group-housed preweaned calves from BLV infection, thereby improving animal health on dairy farms.

Quantitative Risk Assessment for the Introduction of Bovine Leukemia Virus-Infected Cattle Using a Cattle Movement Network Analysis

The cattle industry is suffering economic losses caused by bovine leukemia virus (BLV) and enzootic bovine leukosis (EBL), the clinical condition associated with BLV infection. This pathogen spreads easily without detection by farmers and veterinarians due to the lack of obvious clinical signs. Cattle movement strongly contributes to the inter-farm transmission of BLV. This study quantified the farm-level risk of BLV introduction using a cattle movement analysis. A generalized linear mixed model predicting the proportion of BLV-infected cattle was constructed based on weighted in-degree centrality. Our results suggest a positive association between weighted in-degree centrality and the estimated number of introduced BLV-infected cattle. Remarkably, the introduction of approximately six cattle allowed at least one BLV-infected animal to be added to the farm in the worst-case scenario. These data suggest a high risk of BLV infection on farms with a high number of cattle being introduced. Our findings indicate the need to strengthen BLV control strategies, especially along the chain of cattle movement.

Detection and molecular characterization of bovine leukemia virus in beef cattle presented for slaughter in Egypt

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis, the most common neoplastic disease of cattle worldwide and a serious problem for the cattle industry. Previous studies have shown the molecular prevalence of BLV and the coexistence of BLV genotype-1 and -4 in Egyptian dairy cattle; however, the molecular characteristics of BLV in Egyptian beef cattle are unknown. Therefore, we collected blood samples of 168 beef cattle from slaughterhouses in three governorates in Egypt. Based on BLV-CoCoMo-qPCR-2 targeting long terminal repeats and nested PCR targeting the env-gp51 gene, the BLV provirus infection rates were found to be 47/168 (28.0%) and 42/168 (25.0%), respectively. Phylogenetic analysis based on 501 bp of the BLV env-gp51 gene from 42 BLV isolates revealed that at least six distinctive strains (b, e, f, g, x, and z) were prevalent in cattle across the examined regions. Furthermore, phylogenetic analysis of the 420 bp sequence of the BLV env-gp51 region of the six strains against 11 known genotypes showed that the strains b, e, f, and g were clustered into genotype-1, and strains x and z were clustered into genotype-4. Our results also indicated that strains b and x exist in both dairy and beef cattle in Egypt. The present study is the first to detect and genotype BLV among beef cattle in Egypt.

Detection and Molecular Characterization of Bovine Leukemia Virus in Egyptian Dairy Cattle

Bovine leukemia virus (BLV) causes enzootic bovine leukosis (EBL), the most common neoplastic disease in cattle worldwide. The first EBL outbreak in Egypt was reported in 1997. To date, there are few studies regarding BLV diagnosis using only serological detection and no studies investigating the distribution of BLV provirus, which is the retroviral genome integrated into the host genome, in Egypt. The genetic characteristics of Egyptian BLV strains are also unknown. Therefore, we aimed to detect BLV provirus and determine BLV genetic variability among dairy cattle in Egypt. We collected 270 blood samples of dairy cattle from 24 farms located in five provinces in Egypt. Out of the 270 samples, 58 (21.5%) were positive for BLV provirus. Phylogenetic analysis based on 18 420-bp selected sequences out of 50 isolates of the BLV env-gp51 gene demonstrated that Egyptian BLV isolates were clustered into genotype-1 and-4, among 11 genotypes detected worldwide. Furthermore, phylogenetic analysis and alignment of the 501-bp sequence of the env-gp51 gene revealed that at least six genetically different strains are present in Egypt. Genotype-1 isolates comprised four different strains (G1-a, G1-b, G1-c, and G1-d) and genotype-4 isolates included two different strains (G4-x and G4-y). Moreover, in one farm with 100% infection rate, we identified three isolates of G1-a strain, 35 isolates of G4-x strain, and two isolates of G4-y strain. Overall, this study provides the new report on molecular prevalence of BLV in Egypt and records the coexistence of BLV genotype-1 and-4 in Egyptian cattle.

Seroprevalence and risk factors associated with bovine leukemia virus (BLV) seropositivity in cattle herds from Ecuador

Background: Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis (EBL). This disease mainly affects cattle, causing severe economic losses to producers. Objective: To establish individual and herd seroprevalence and determine the risk factors associated with BLV seropositivity for dairy and dual-purpose cattle herds in Ecuador. Methods: A total of 2,668 serum samples from 386 herds were collected. A questionnaire, including variables related to cattle health, management and the environment was completed by each herd. A commercial blocking enzyme-linked immunosorbent assay (ELISA) test was used to determine seropositivity. A generalized estimating equation model (GEE) was developed to determine the factors associated with BLV seropositivity. Results: Individual seroprevalence of BLV infection in Ecuador was 17.3% (CI95% = 15.86-18.74%). Herd prevalence was 37.8% (CI95% = 33.0-42.6%), and intra-herd prevalence ranged between 12.5 and 100% (median: 37.5%). The risk factors associated with BLV seropositivity were artificial insemination (OR: 2,215; CI95% = 1.402-3.501), concrete floors (OR: 2.178; CI95% = 1.217-3.889), presence of wild ruminants (OR: 2.998; CI95% = 1.788-5.027), and sampling season (wet; OR: 1.996; CI95% = 1.140-3.497). Conclusions: Results indicate that BLV is widespread in cattle herds in Ecuador. In addition, the study suggests that a control program to fight BLV infection should focus on controlling the risk factors identified.

Phylogenetic Analysis of South African Bovine Leukaemia Virus (BLV) Isolates

Bovine leukaemia virus (BLV) causes chronic lymphoproliferative disorder and fatal lymphosarcoma in cattle, leading to significant economic losses in the beef and dairy industries. BLV is endemic globally and eleven genotypes have been identified. To date, only Zambian isolates have been genotyped from Africa. Although high BLV prevalence has been reported in South Africa, there has been no molecular characterisation of South African BLV isolates. To characterise BLV isolates in South Africa for the first time, we investigated the phylogenetic relationships and compared the genetic variability of eight South African BLV isolates with BLV isolates representing the eleven known genotypes from different geographical regions worldwide. Phylogenetic analyses based on full-length and partial env sequences as well as full-length gag sequences revealed that at least two genotypes, genotypes 1 (G1) and 4 (G4), are present in cattle in South Africa, which is consistent with studies from Zambia. However, our analysis revealed that the G1 South African isolate is more similar to other G1 isolates than the G1 Zambian isolates whereas, the G4 South African isolates are more divergent from other G4 isolates but closely related to the G4 Zambian isolate. Lastly, amino acid sequence alignment identified genotype-specific as well as novel amino acid substitutions in the South African isolates. The detection of two genotypes (G1 and G4) in southern Africa highlights the urgent need for disease management and the development of an efficacious vaccine against local strains.

Detection of genotype 1 bovine leukemia virus from a C.schultzei pool: Do Culicoides spp. have a role on the transmission of bovine leukemia virus?

Bovine leukemia virus (BLV) is known as the etiological agent of Enzootic bovine leukosis (EBL), which is the most common neoplastic disease of cattle. While the major route of virus transmission is believed to be iatrogenic, BLV proviral DNA has been identified in biological materials, including nasal secretions, saliva, milk, colostrum, and semen, and in several insect species, including horses flies. However, insects' role in the natural transmission of BLV has not been clearly demonstrated. This study assessed the possible role of midges - Culicoides spp. - in BLV transmission. BLVs were genetically characterized and BLV infection seroprevelance was determined in 224 cattle sampled from 27 different small family herds in five different districts in Hatay province, southern Turkey. Out of the 25 Culicoides spp. pools, one (4.0%; 1/25) was a C.schultzei pool while 2.67% (6/224) of the sampled cattle were positive for BLV nucleic acid. The seroprevalance rates for the sampled herds and all sampled cattle were 7.40% (2/27) and 1.33% (3/224), respectively. According to the phylogenetic analysis, the sequences of the BLVs from the cattle (n = 6) and the one BLV-positive C.schultzei pool clustered on genotype 1 (G1) BLVs. Although these results do not reveal the exact role of Culicoides spp. or other midges flies in BLV transmission, the simultaneous presence of same substitions in BLVs from both cattle and a C.schultzei pool is noteworthy. Further studies on the env gene and other BLV gene regions detected from cattle and C.schultzei pools are ongoing to understand the possible epidemiological relationship between cattle and flies.

Herd management practices associated with bovine leukemia virus incidence rate in Michigan dairy farms

The objective of this study was to identify associations between herd management practices and the incidence rate of bovine leukemia virus (BLV) infections in Michigan dairy herds. Previous management risk factor studies were of antibody prevalence rather than the rate of recent infections. Milk samples were collected from cohorts of cows on 112 Michigan dairy herds and tested for BLV using an antibody capture ELISA (n = 3849 cows). Cows were subsequently followed for an average of 21 months. Cows negative for anti-BLV antibodies and still present in their respective herds were retested by the same antibody capture ELISA to estimate within-herd incidence rates. The overall crude incidence rate was 1.46 infections per 100 cow-months at risk for the 1314 retested cows in 107 herds. The average within-herd incidence rate was 2.28 infections per 100 cow-months (range: 0 to 9.76 infections per 100 cow-months). A negative binomial regression model was used to identify herd management practices associated with the within-herd incidence rate. Results of the final multivariable model identified higher herd prevalence, milking frequency, needle reuse, as well as housing post-parturient cows separately, to be associated with increased incidence rate. Utilization of sand bedding for the lactating herd was found to be associated with decreased incidence rates. Results of this study suggest potential routes of BLV transmission which should be further investigated as disease control targets in ongoing control programs.

New evidence of bovine leukemia virus circulating in Myanmar cattle through epidemiological and molecular characterization

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis, which is the most common neoplastic disease of cattle. BLV infects cattle worldwide and causes serious problems for the cattle industry. In this study, we examined the prevalence of BLV infection and the distribution of BLV genotypes in cattle in the northern, central, and southern parts of Myanmar. The prevalence of BLV infection among Myanmar cattle (37.04%) in this study was markedly higher than the prevalence (9.1%) observed in our earlier study in which BLV was detected from the limited number of cattle only from a small area of Myanmar. Phylogenetic analysis of partial env-gp51 sequence of the isolated BLV strains revealed that there are at least three BLV genotypes (genotype-1, genotype-6, and genotype-10) in Myanmar, which have also been detected in the neighboring countries. We performed this study to estimate the BLV proviral load, which is a major diagnosis index for determining the virus transmission risk. The cattle of the three test regions with warm, wet, and humid climatic conditions (upper Sagaing, Yangon, and Kayin) exhibited a high mean proviral load, while cattle of three other regions with low annual rainfall and very high temperature (Mandalay, Magway, and upper Bago) exhibited a low mean proviral load. Further, the level of proviral load and the prevalence of BLV infection in Myanmar native cattle (N = 235) were lower than that in the hybrid cattle (Holstein Friesian × Myanmar native) (N = 62). We also observed that the cattle with high risk for BLV transmission, which have high proviral load, may enhance the BLV infection rate. Hence, to control BLV transmission, it is necessary to eliminate these cattle with high-risk for BLV transmission and to diagnose BLV provirus in cattle in the remaining regions/states of Myanmar sharing a boundary with neighboring countries.

Molecular Epidemiological and Serological Studies of Bovine Leukemia Virus in Taiwan Dairy Cattle

Bovine leukemia virus (BLV) infection results in a decrease in milk yield and quality, a compromise in immunity, and shortening in the longevity of cows. The current status of BLV infection of dairy cattle in Taiwan remains unclear. To evaluate BLV infection, anti-BLV gp51 antibody and proviral DNA were detected. Surprisingly, the seroprevalence of BLV at the animal and herd level was as high as 81.8% (540/660 cattle) and 99.1% (109/110 herds), respectively. Among 152 blood samples analyzed, 132 (86.8%) were detected as positive for BLV-proviral DNA. When the complete blood count (CBC) was taken into account, the white blood cell (WBC) number appears to be the factor with the highest predicted potential for BLV infection. Moreover, based on receiver operating characteristic (ROC) curve analysis, the sensitivity and specificity are 72.0 and 75.0%, respectively, when the cut-off value of the WBC was set at 10.215 K/μL. Despite the co-circulation of genotype 1 and 3 in Taiwan, genotype 1 was much more prevalent (29/30). Taken together, due to the high prevalence of BLV, the identification of risk factors for interrupting the routes of transmission of BLV are critical for the control and prevention of further BLV infection.

Detection and molecular characterization of bovine leukemia virus in various regions of Iran

Purpose. Bovine leukemia virus (BLV) infects cattle worldwide, imposing an economic impact on the dairy cattle industry. The purpose of this study was to evaluate the molecular epidemiology of BLV in Iran.Methodology. Blood samples taken from 280 cows aged over 2 years old from 13 provinces of Iran were used for leukocyte count and blocking ELISA. Genomic DNA was extracted from the peripheral blood leukocytes of BLV-infected samples and fetal lamb kidney cells to perform PCR of partial env, rex and tax genes and long-terminal-repeat region. The PCR products were sequenced, the phylogenetic tree of each gene was constructed, and nucleotide and amino acid sequence pair distances were calculated.Results. The frequency of BLV infection was 32.8 % among animals and was 80 % among provinces. In BLV seropositive animals, the rate of persistent lymphocytosis was 36.9 %. The constructed phylogenetic trees showed the presence of two BLV genotypes (1 and 4) in Iranian strains. As previous studies, our results showed that the env gene was more variable than previously thought, the Rex protein could withstand more amino acid changes compared to the Tax protein, and no significant differences were observed in average changes of the nucleotide of these genes between clinical stages.Conclusions. Our data indicates an increase in the frequency of this infection in Iran. This is the first study report of the presence of BLV genotype 4 in Iranian farms. These findings may have an important role in the control and prevention of BLV infection in Iran and other countries.

Epidemiology and genetic diversity of bovine leukemia virus

Bovine leukemia virus (BLV), an oncogenic member of the Deltaretrovirus genus, is closely related to human T-cell leukemia virus (HTLV-I and II). BLV infects cattle worldwide and causes important economic losses. In this review, we provide a summary of available information about commonly used diagnostic approaches for the detection of BLV infection, including both serological and viral genome-based methods. We also outline genotyping methods used for the phylogenetic analysis of BLV, including PCR restriction length polymorphism and modern DNA sequencing-based methods. In addition, detailed epidemiological information on the prevalence of BLV in cattle worldwide is presented. Finally, we summarize the various BLV genotypes identified by the phylogenetic analyses of the whole genome and env gp51 sequences of BLV strains in different countries and discuss the distribution of BLV genotypes worldwide.

Bovine leukaemia virus DNA in fresh milk and raw beef for human consumption

Bovine leukaemia virus (BLV) is the causative agent of enzootic bovine leucosis, which has been reported worldwide. BLV has been found recently in human tissue and it could have a significant impact on human health. A possible hypothesis regarding viral entry to humans is through the consumption of infected foodstuffs. This study was aimed at detecting the presence of BLV DNA in raw beef and fresh milk for human consumption. Nested PCR directed at the BLV gag gene (272 bp) was used as a diagnostic test. PCR products were confirmed by Sanger sequencing. Forty-nine per cent of the samples proved positive for the presence of proviral DNA. This is the first study highlighting the presence of the BLV gag gene in meat products for human consumption and confirms the presence of the viral DNA in raw milk, as in previous reports. The presence of viral DNA in food products could suggest that viral particles may also be found. Further studies are needed to confirm the presence of infected viral particles, even though the present findings could represent a first approach to BLV transmission to humans through foodstuff consumption.

Lifetime effects of infection with bovine leukemia virus on longevity and milk production of dairy cows

Enzootic bovine leukosis (EBL) is an economically important disease of dairy cattle caused by bovine leukemia virus (BLV). The economic impacts of the infection have been debated in the literature. The present study was conducted to determine the lifetime effects of BLV infection on longevity and milk production of dairy cows in Canada. The data were aggregated from a combination of two data sets: 1) BLV serum-ELISA test results from Canada-wide surveys of production limiting diseases, which took place between 1998 and 2003 in 8 provinces, and 2) longitudinal production data for all cows in the former study, extracted from the Canadian dairy herd improvement database. All participant cows had been culled or died by the onset of this study. A historical cohort study was designed, including cows which tested positive to BLV-antibodies in their first lactation (positive cohort, n=1858) and cows which tested negative in their second or later lactations (negative cohort, n=2194). To assess the impacts of infection with BLV on longevity (the number of lifetime lactations), a discrete-time survival analysis was carried out. The effect of BLV on the lifetime milk production (the sum of all life 305-day milk production) was evaluated using a multilevel linear regression model. Overall, 4052 cows from 348 herds met the eligibility criteria and were enrolled in the study. In the longevity model, the interaction term between time (lactation number) and BLV-status was highly significant. Cows which were positive to BLV had consistently greater probabilities of being culled (or dying) than the test-negative cows. In the milk production model, the interaction term between BLV-status and longevity of the cows was highly significant; indicating that lifetime BLV effects on the total milk production was dependent on the lactation in which the study cows were culled/died. Infected cows with 2 and 3 lactations showed significantly lower life milk productions [-2554kg (-3609 to -1500) and -1171kg (-2051 to -292), respectively] compared with their negative counterparts with 2 and 3 lactations. As the cows lived longer (>3 lactations), the differences in life milk production between the two cohorts were no longer significant. Overall, it was predicted that the test-positive cows produced substantially lower milk compared to the test-negative cows throughout their study lifespans. With the high prevalence of BLV in Canadian dairy cows and its detrimental economic impacts, pursuing broad-based control programs in Canada should be evaluated.

Short communication: Relationship between the level of bovine leukemia virus antibody and provirus in blood and milk of cows from a naturally infected herd

We explored the relationship between the level of bovine leukemia virus antibodies and provirus load during natural infection. For that purpose, a set of 50 blood and milk paired samples were analyzed for the presence of bovine leukemia virus provirus and antibodies. Additionally, provirus load and antibody titers were measured and the relationship between these variables was investigated. Bovine leukemia provirus was detected in 59% of milk samples and a negative correlation was observed between the level of milk provirus load and milk antibody titers. By the consumption of raw milk, calves might be exposed to bovine leukemia virus favoring the perinatal transmission of this disease.

Bovine leukemia virus infection in cattle of China: Association with reduced milk production and increased somatic cell score

The main objective of this study was to investigate the individual cow effect of bovine leukemia virus (BLV) infection on milk production and somatic cell score (SCS). The fluorescence resonance energy transfer (FRET) quantitative PCR established in this study and a commercial ELISA kit revealed that 49.1% of dairy cattle (964/1,963) from 6 provinces of China and 1.6% of beef cattle (22/1,390) from 15 provinces were BLV positive. In a detailed study of 105 cows, BLV was found most commonly in buffy coat samples that also had highest copy numbers (10(4.75±1.56) per mL); all cows negative for BLV in buffy coat samples were also negative in vaginal swab, milk, and fecal samples. Copy numbers of BLV were 10(2.90±0.42)/gram of feces, 10(0.83±0.62)/mL of milk, and 10(2.18±0.81) per vaginal swab. The BLV-positive cows had significantly lower milk production in the early (26.8 vs. 30.9kg) and middle stages of lactation (22.2 vs. 26.1kg) in animals with ≥4 parities than the BLV-negative cows; they also had significantly higher SCS in early and middle lactation stages (early=5.2 vs. 4.3; middle=4.9 vs. 3.9) in animals with ≥4 parities. Milk production and SCS did not significantly differ between the BLV-infected and -uninfected cows when they were in the late lactation stage or in animals with ≤3 parities. Taken together, our results indicate that BLV infections are widespread in the dairy farms of China. Vaginal secretions and feces may be involved in BLV transmission. A BLV infection may result in reduced milk yield and increased SCS in a parity and lactation stage-restricted manner.

Risk factors associated with increased bovine leukemia virus proviral load in infected cattle in Japan from 2012 to 2014

Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis, a malignant B cell lymphoma. BLV has spread worldwide and causes serious problems. After infection, the BLV genome is integrated into the host DNA and can be amplified during periods of latency. We previously designed degenerate primers using the Coordination of Common Motifs (CoCoMo) algorithm to establish a new quantitative real-time PCR method (BLV-CoCoMo-qPCR-2) of measuring the proviral load of both known and novel BLV variants. Here, we aimed to examine the correlation between proviral load and risk factors for BLV infection, such as breeding systems, parousity, and colostrum feeding. Blood and serum samples were collected from 83 BLV-positive farms in 22 prefectures of Japan, and the BLV proviral load and anti-BLV antibody levels were measured. BLV was detected in 73.3% (1039/1,417) of cattle by BLV-CoCoMo-qPCR-2 and the provirus was detected in 93 of 1039 antibody-negative samples. The results showed that the proviral load increased with progression of lymphocytosis. Next, the risk factors associated with increasing BLV infection rate were examined along with any association with proviral load. The proviral load was higher in cattle with lymphocytosis than in healthy cattle, and higher in multiparous cows than in nulliparous cows. Finally, proviral loads were higher in contact breeding systems than in non-contact breeding systems. Taken together, these findings may help to formulate a plan for eliminating BLV from contaminated farms. This is the first nationwide study to estimate BLV proviral load in Japanese cattle.

Detection of the BLV provirus from nasal secretion and saliva samples using BLV-CoCoMo-qPCR-2: Comparison with blood samples from the same cattle

Bovine leukemia virus (BLV) induces enzootic bovine leukosis, which is the most common neoplastic disease in cattle. Sero-epidemiological studies show that BLV infection occurs worldwide. Direct contact between infected and uninfected cattle is thought to be one of the risk factors for BLV transmission. Contact transmission occurs via a mixture of natural sources, blood, and exudates. To confirm that BLV provirus is detectable in these samples, matched blood, nasal secretion, and saliva samples were collected from 50 cattle, and genomic DNA was extracted. BLV-CoCoMo-qPCR-2, an assay developed for the highly sensitive detection of BLV, was then used to measure the proviral load in blood (n=50), nasal secretions (n=48), and saliva (n=47) samples. The results showed that 35 blood samples, 14 nasal secretion samples, and 6 saliva samples were positive for the BLV provirus. Matched blood samples from cattle that were positive for the BLV provirus (either in nasal secretion or saliva samples) were also positive in their blood. The proviral load in the positive blood samples was >14,000 (copies/1×10(5) cells). Thus, even though the proviral load in the nasal secretion and saliva samples was much lower (<380 copies/1×10(5) cells) than that in the peripheral blood, prolonged direct contact between infected and healthy cattle may be considered as a risk factor for BLV transmission.

Horizontal transmission and phylogenetic analysis of bovine leukemia virus in two districts of Miyazaki, Japan

Horizontal transmission is recognized as a major infection route for bovine leukemia virus (BLV), and cattle with high viral loads are considered to be a major infectious source in a herd. However, a correlation between viral loads and the risk of infection has been insufficient to use as a foundation for BLV control strategies. In this report, we examined the epidemiology of BLV infection and the infectious source in a local area. In 2013–2014, BLV infection was investigated in 1,823 cattle from 117 farms in two adjacent districts, Miyazaki, Japan. Seropositive samples for BLV were detected with 88 cattle and in 14 farms. Phylogenetic analysis revealed that 94% of the isolates clustered into genotype I and the remaining isolate into genotype III. Among genotype I, genetically distinct strains were spread at each farm, and cattle infected with less than 3 copies/100 cells did not transmit BLV to other cattle for more than thirty months. This is the first report of concrete data of viral load in relation to viral horizontal transmission under the field condition. The data facilitate farmers and veterinarians understanding the status of BLV infected cattle. This research contributes to BLV infection control and the development of effective BLV eradication programs.

A homogenous fluorescence quenching based assay for specific and sensitive detection of influenza virus A hemagglutinin antigen

Influenza pandemics cause millions of deaths worldwide. Effective surveillance is required to prevent their spread and facilitate the development of appropriate vaccines. In this study, we report the fabrication of a homogenous fluorescence-quenching-based assay for specific and sensitive detection of influenza virus surface antigen hemagglutinins (HAs). The core of the assay is composed of two nanoprobes namely the glycan-conjugated highly luminescent quantum dots (Gly-QDs), and the HA-specific antibody-modified gold nanoparticle (Ab-Au NPs). When exposed to strain-specific HA, a binding event between the HA and the two nanoprobes takes place, resulting in the formation of a sandwich complex which subsequently brings the two nanoprobes closer together. This causes a decrease in QDs fluorescence intensity due to a non-radiative energy transfer from QDs to Au NPs. A resulting correlation between the targets HA concentrations and fluorescence changes can be observed. Furthermore, by utilizing the specific interaction between HA and glycan with sialic acid residues, the assay is able to distinguish HAs originated from viral subtypes H1 (human) and H5 (avian). The detection limits in solution are found to be low nanomolar and picomolar level for sensing H1-HA and H5-HA, respectively. Slight increase in assay sensitivity was found in terms of detection limit while exposing the assay in the HA spiked in human sera solution. We believe that the developed assay could serve as a feasible and sensitive diagnostic tool for influenza virus detection and discrimination, with further improvement on the architectures.

Prevalence of bovine leukemia virus (BLV) infection in the northeast of Iran

The purpose of this study was to determine the prevalence of bovine leukemia virus (BLV) in Khorasan Razavi and Khorasan Shomali provinces which are the main provinces located in the northeast of Iran. Total number of 429 blood samples were collected from industrial dairy herds. The samples were categorized based on province, age (2-3, 4-6, and 7-10 years old), calving (≤ 2, 3-5, and > 5) and herd size (≤ 100, 101-250, and > 250) and examined by indirect ELISA. The results of this study showed that 109 (25.4%) out of 429 serum samples were BLV seropositive. The BLV prevalence among cattle of dairy herds of Khorasan Razavi and Khorasan Shomali provinces were 29.8% and 1.5%, respectively. The results showed that the number of seropositive animals was increased significantly with the age (p < 0.05). The infection rate in animals 2-3, 4-6 and 7-10 years old were 12.1%, 26.7% and 45.6%, respectively. It was shown that BLV prevalence according to calving ≤ 2, 3-5 and > 5 was 15.5%, 33.0% and 42.9%, respectively, with a significant difference between calving ≤ 2 and > 5 (p < 0.001). The prevalence of BLV among herd size of ≤ 100, 101-250 and > 250 was 19.7%, 14.3% and 42.1%, respectively, which was significantly higher in herds with more than 250 cattle (p < 0.05). This study revealed that BLV infection in dairy herds of northeast of Iran was influenced by geographical location (province), age, calving and herd size.

BLV-CoCoMo-qPCR: a useful tool for evaluating bovine leukemia virus infection status

BACKGROUND

Bovine leukemia virus (BLV) is associated with enzootic bovine leukosis, which is the most common neoplastic disease of cattle. BLV infects cattle worldwide, imposing a severe economic impact on the dairy cattle industry. Recently, we developed a new quantitative real-time polymerase chain reaction (PCR) method using Coordination of Common Motifs (CoCoMo) primers to measure the proviral load of known and novel BLV variants in BLV-infected animals. Indeed, the assay was highly effective in detecting BLV in cattle from a range of international locations. This assay enabled us to demonstrate that proviral load correlates not only with BLV infection capacity as assessed by syncytium formation, but also with BLV disease progression. In this study, we compared the sensitivity of our BLV-CoCoMo-qPCR method for detecting BLV proviruses with the sensitivities of two real-time PCR systems, and also determined the differences of proviral load with serotests.

RESULTS

BLV-CoCoMo-qPCR was found to be highly sensitive when compared with the real-time PCR-based TaqMan MGB assay developed by Lew et al. and the commercial TaKaRa cycleave PCR system. The BLV copy number determined by BLV-CoCoMo-qPCR was only partially correlated with the positive rate for anti-BLV antibody as determined by the enzyme-linked immunosorbent assay, passive hemagglutination reaction, or agar gel immunodiffusion. This result indicates that, although serotests are widely used for the diagnosis of BLV infection, it is difficult to detect BLV infection with confidence by using serological tests alone. Two cattle were experimentally infected with BLV. The kinetics of the provirus did not precisely correlate with the change in anti-BLV antibody production. Moreover, both reactions were different in cattle that carried different bovine leukocyte antigen (BoLA)-DRB3 genotypes.

CONCLUSIONS

Our results suggest that the quantitative measurement of proviral load by BLV-CoCoMo-qPCR is useful tool for evaluating the progression of BLV-induced disease. BLV-CoCoMo-qPCR allows us to monitor the spread of BLV infection in different viewpoint compared with classical serotest.

Herd-level determinants of bovine leukaemia virus prevalence in dairy farms

The prevalence of bovine leukaemia virus (BLV) was determined in 113 Michigan dairy herds by ELISA testing for anti-BLV antibodies in milk. Additionally, an interview regarding management practices with cooperating herd managers identified farm-level variables thought to be associated with prevalence of BLV. Twenty-three risk factors (P ⩽ 0·1) were identified on one-way ANOVA or simple linear regression. Multivariate analysis identified several management practices whose predictive value for increased prevalence of BLV may relate to transmission among herd mates, e.g. reuse of hypodermic needles, lack of fly control, gouge dehorning and increased use of injections in dry cows. Additionally, exclusive breeding of heifers with artificial insemination was associated with decreased BLV prevalence, as compared with at least some use of natural service by a bull. Although intervention studies are needed before causal relationships can be concluded, and unaccounted variables related to transmission exist among dairy herds, these findings suggest management practices that may help dairy producers reduce the transmission of BLV within their herds.