Enzootic bovine leukosis: Report of eradication and surveillance measures in Italy over an 8-year period (2005–2012)

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.

Development of droplet digital PCR for quantification of bovine leukemia virus proviral load using unpurified genomic DNA

Bovine leukemia virus (BLV) is the causative agent of a B-cell tumor called enzootic bovine leukosis. Preventing BLV spreading is required to reduce economic loss related to BLV infection of livestock. To quantify proviral load (PVL) more easily and rapidly, we developed a quantification system of PVL using droplet digital PCR (ddPCR). This method uses a multiplex TaqMan assay of the BLV provirus and housekeeping gene RPP30 for the quantification of BLV in BLV-infected cells. Furthermore, we combined ddPCR with DNA purification-free sample preparation (unpurified genomic DNA). The percentage of BLV-infected cells based on unpurified genomic DNA was highly correlated with that based on purified genomic DNA (correlation coefficient: 0.906). Thus, this new technique is a suitable method to quantify PVL of BLV-infected cattle in a large sample number.

Identifying Pathogen and Allele Type Simultaneously in a Single Well Using Droplet Digital PCR

In the transmission control of chronic and untreatable livestock diseases such as bovine leukemia virus (BLV) infection, the removal of viral superspreaders is a fundamental approach. On the other hand, selective breeding of cattle with BLV-resistant capacity is also critical for reducing the viral damage to productivity by keeping infected cattle. To provide a way of measuring BLV proviral load (PVL) and identifying susceptible/resistant cattle simply and rapidly, we developed a fourplex droplet digital PCR method targeting the BLV pol gene, BLV-susceptible bovine major histocompatibility complex (BoLA)-DRB3*016:01 allele, resistant DRB3*009:02 allele, and housekeeping RPP30 gene (IPATS-BLV). IPATS-BLV successfully measured the percentage of BLV-infected cells and determined allele types precisely. Furthermore, it discriminated homozygous from heterozygous carriers. Using this method to determine the impact of carrying these alleles on the BLV PVL, we found DRB3*009:02-carrying cattle could suppress the PVL to a low or undetectable level, even with the presence of a susceptible heterozygous allele. Although the population of DRB3*016:01-carrying cattle showed significantly higher PVLs compared with cattle carrying other alleles, their individual PVLs were highly variable. Because of the simplicity and speed of this single-well assay, our method has the potential of being a suitable platform for the combined diagnosis of pathogen level and host biomarkers in other infectious diseases satisfying the two following characteristics of disease outcomes: (i) pathogen level acts as a critical maker of disease progression; and (ii) impactful disease-related host genetic biomarkers are already identified. IMPORTANCE While pathogen-level quantification is an important diagnostic of disease severity and transmissibility, disease-related host biomarkers are also useful in predicting outcomes in infectious diseases. In this study, we demonstrate that combined proviral load (PVL) and host biomarker diagnostics can be used to detect bovine leukemia virus (BLV) infection, which has a negative economic impact on the cattle industry. We developed a fourplex droplet digital PCR assay for PVL of BLV and susceptible and resistant host genes named IPATS-BLV. IPATS-BLV has inherent merits in measuring PVL and identifying susceptible and resistant cattle with superior simplicity and speed because of a single-well assay. Our new laboratory technique contributes to strengthening risk-based herd management used to control within-herd BLV transmission. Furthermore, this assay design potentially improves the diagnostics of other infectious diseases by combining the pathogen level and disease-related host genetic biomarker to predict disease outcomes.

Development of a droplet digital PCR assay for quantification of the proviral load of bovine leukemia virus

Droplet digital PCR (ddPCR) is a highly sensitive tool developed for the detection and quantification of short-sequence variants—a tool that offers unparalleled precision enabling measurement of smaller-fold changes. We describe here the use of ddPCR for the detection of Bovine leukemia virus (BLV) DNA provirus. Serum samples and whole blood from experimentally infected sheep and naturally infected cattle were analyzed through ddPCR to detect the BLV gp51 gene, and then compared with serologic and molecular tests. The ddPCR assay was significantly more accurate and sensitive than AGID, ELISA, nested PCR, and quantitative PCR. The limit of detection of ddPCR was 3.3 copies/µL, detecting positive experimentally infected sheep beginning at 6 d post-infection. The ddPCR methodology offers a promising tool for evaluating the BLV proviral load, particularly for the detection of low viral loads.

BVDV, BHV-1 and BLV antibodies in dromedary camels of Turkey kept without and with ruminants

Camels are the only animals bred to sustain the tradition of wrestling in Turkey and are reared within a limited set of geographic areas. Farmers of such animals may also be engaged in ruminant breeding. The current research was aimed at documenting bovine viral diarrhoea virus (BVDV), bovine herpesvirus-1 (BHV-1), and bovine leukaemia virus (BLV) infections in sera collected from dromedary camels in four different geographical regions of Turkey during the years 2019-2021. All samples were tested for BVDV, BHV-1 and BLV antibodies as well as BVDV antigen by ELISA. Antibodies against BVDV were found in 16.8% of the camel sera tested. However, none of the camels sampled were positive in terms of BHV-1 and BLV antibodies as well as BVDV antigen. The prevalence was observed higher in the herds in which ruminants were raised in addition to camels (OR = 4.583, 95% CI, 1.298-16.182), (p = 0.018), while the prevalence was observed lower in the herds in which only camels were raised. This study showed that BVDV infection was more prevalent than BHV-1 and BLV infections in Turkish dromedary camels. Herewith, the camels, being a susceptible species to numerous viral ruminant diseases, may also serve as an important source of BVDV infection for other ruminant animals in the same flock.

Evidence of bovine leukemia virus circulating in sheep and buffaloes in Colombia: insights into multispecies infection

Bovine leukemia virus (BLV) is the causative agent of leukemia/lymphoma in cattle. However, previous evidence has shown its presence in other species of livestock as well as in humans, suggesting that other species can be accidental hosts of the virus. In viral infections, receptors that are common to different animal species are proposed to be involved in cross-species infections. For BLV, AP3D1 has been proposed to be its receptor, and this protein is conserved in most mammalian species. In Colombia, BLV has been reported in cattle with high prevalence rates, but there has been no evidence of BLV infections in other animal species. In this study, we tested for the virus in sheep (n = 44) and buffaloes (n = 61) from different regions of Colombia by nested PCR, using peripheral blood samples collected from the animals. BLV was found in 25.7% of the animals tested (12 buffaloes and 15 sheep), and the results were confirmed by Sanger sequencing. In addition, to gain more information about the capacity of the virus to infect these species, the predicted interactions of AP3D1 of sheep and buffaloes with the BLV-gp51 protein were analyzed in silico. Conserved amino acids in the binding domains of the proteins were identified. The detection of BLV in sheep and buffaloes suggests circulation of the virus in multiple species, which could be involved in dissemination of the virus in mixed livestock production settings. Due to the presence of the virus in multiple species and the high prevalence rates observed, integrated prevention and control strategies in the livestock industry should be considered to decrease the spread of BLV.

Seropositivity and risk factors associated with the presentation of bovine leukosis virus in Sotaquirá, Colombia

Background and Aim

Enzootic bovine leukosis is a disease economically important to the dairy farming industry worldwide. The virus is of the Deltaretrovirus genus and is primarily transmitted iatrogenically. Most bovines infected with the virus remain asymptomatic with only 5-10% of cattle having lymphomas. This study aimed to determine the seroprevalence of bovine leukosis virus (BLV) in Sotaquirá, Boyacá, Colombia.

Materials and Methods

We conducted a descriptive, observational epidemiological cross-sectional study using the simple random sampling method with a sample size of 1000. Blood samples from random bovine were processed using the SERELISA^® BLV Ab Mono Blocking indirect enzyme-linked immunosorbent assay kit (Zoetis, USA). The assay had a sensitivity of 97% and a specificity of 98%. The collected data were processed using Epi Info^® (Centers for Disease Control and Prevention; Atlanta, Georgia). From the study, we could determine a high seroprevalence of BLV in Sotaquirá.

Results

We established a high seroprevalence on BLV in the municipality, with 31.1% apparent seroprevalence and 30.6% real seroprevalence rate. We found that male cattle more than 4 years old (39.4%) and the Ayrshire breed (45.5%) had the highest prevalence rates of the virus. In this study, we could establish statistically significant associations according to breed, age, and gender of the cattle under study. Moreover, we identified the risk factors for BLV infection. We found that in cattle aged <1 year and those older than 4 years of age and those of the Holstein breed, the presentation of infectious bovine rhinotracheitis, mucosal secretions, mastitis, fetal death, the presence of a corral, and the implementation of artificial insemination practices were risk factors for BLV infection.

Conclusion

Determining the prevalence of BLV within the herd and identifying the associated risk factors for the disease are fundamental in developing efficient programs for the control and eradication of BLV within herds.

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).

Overview of Control Programs for EU Non-regulated Cattle Diseases in Italy

The cattle industry is a major driving force for the Italian agricultural sector totalling about 5. 6 million heads for dairy and meat production together. It is particularly developed in the northern part of the country, where 70% of the whole Italian cattle population is reared. The cattle industry development in the rest of the country is hampered by the hard orography of the territories and a variety of socioeconomic features leading to the persistence of the traditional rural farming systems. The differences in the farming systems (industrial vs. traditional) also affect the health status of the farms. Whereas, Enzootic Bovine Leukosis (EBL) is almost eradicated across the whole country, in Southern Italy where Bovine Tuberculosis and Brucellosis are still present and Bluetongue is endemic due to the presence of the competent vector (Culicoides imicola), less investments are aimed at controlling diseases with economic impact or at improving farm biosecurity. On the other hand, with the eradication of these diseases in most part of the country, the need has emerged for reducing the economic burden of non-regulated endemic disease and control programs (CPs) for specific diseases have been implemented at regional level, based on the needs of each territory (for instance common grazing or trading with neighboring countries). This explains the coexistence of different types of programs in force throughout the country. Nowadays in Italy, among cattle diseases with little or no EU regulations only three are regulated by a national CP: Enzootic Bovine Leukosis, Bluetongue and Paratuberculosis, while Bovine Genital Campylobacteriosis and Trichomonosis are nationwide controlled only in breeding bulls. For some of the remaining diseases (Infectious Bovine Rhinotracheitis, Bovine Viral Diarrhea, Streptococcus agalactiae) specific CPs have been implemented by the regional Authorities, but for most of them a CP does not exist at all. However, there is a growing awareness among farmers and public health authorities that animal diseases have a major impact not only on the farm profitability but also on animal welfare and on the use of antibiotics in livestock. It is probable that in the near future other CPs will be implemented.

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.

Retrospective analysis of the epizootic situation of enzootic bovine leukosis in Ukraine in 1994–2019

In Ukraine, prevention and control measures of bovine leukosis were regulated by relevant legislation, regulations and instructions developed in the period 1960–1992. Currently, the instruction on prevention and rehabilitation of this disease in cattle is used (approved in 2007). According to it, the identification of infected animals is carried out from 6 months of age by serological (first scheme in AGID or another in ELISA) and genomic (PCR) methods. The infected animals are removed from the herd or slaughtered. In general, because of the diagnostic and preventive measures carried out during the analyzed period (26 years) 10 519 farms were rehabilitated from leukosis (2 346 affected farms remained from previous years). At the same time, more 4 million infected cattle were slaughtered. The majority of affected farms (more than 1 000) were registered in the period between 1994 (2 346 farms) and 2003 (1 247 farms). Since 2014, the number of affected farms has remained mostly below 10 and the number of infected cattle has decreased to 2 000 animals per year. At the same time, the number of rehabilitated farms also decreased (from 1 307 farms in 1998 to 4 farms in 2014). The same trend was registered with the dynamics of the number of animals that were removed from the herd due to leukosis. Thus, in 1995 and 1997 their numbers were 321 178 and 558 649 animals, respectively, and in 2014 it was 1 124. The obtained indicators of intensity and extensiveness of the epizootic process show that the incidence rate was maximal during 1998–2000 and amounted to 3.7–4.3%. The maximum indicators of the coefficient of affection were recorded in 1997–2000 and equal 11.8–15.3%. The rate of foci remained on the level of 90–270 throughout the all analyzed period. During 2008–2019, specialists of the Ukrainian veterinary laboratories investigated more than 47 million samples of cattle blood sera for enzootic bovine leukosis by AGID and ELISA. However, despite the significant diagnostic work, the important factor in the decrease of the number of affected farms and infected animals is the decrease in the total number of cattle in Ukraine (almost 22 million animals in 1994 against 3 million in 2019). Graphic trends of these indicators are comparable and agree with the decrease in the number of cattle in our country by analyzed period. After 2014, the number of affected farms ranged 10–17 per year (mostly in private households). However, the full recovery of cattle in Ukraine from bovine leukosis has not taken place, although our country is closer than ever to this.

Detection and genotyping of bovine leukemia virus (BLV) in Vietnamese cattle

Bovine leukemia virus (BLV) belongs to the genus, Deltaretrovirus of the family, Retroviridae and it is the causative agent of enzootic bovine leukosis. The prevalence of BLV in three provinces in the Red River Delta Region in the North of Vietnam, Hanoi, Vinhphuc and Bacninh was studied from April 2017 to June 2018. A total of 275 blood samples collected from cattle were used for serum isolation and DNA extraction. Of these samples, 266 sera were subjected to ELISA test for detecting antibody against BLV gp51 protein and 152 DNA samples were used to detect the 444 bp fragment corresponding to a part of the gp51 region of the env by nested PCR. The results showed that 16.5% (n=44) and 21.1% (n=32) of samples were positive for BLV gp51 antibody and BLV proviral DNA, respectively. Phylogenetic analysis of the partial (423 bp) and complete (913 bp) BLV env-gp51 gene indicated that Vietnamese strains were clustered into genotypes 1, 6 and 10 (G1, G6 and G10). Of those genotypes, G1 genotype was dominant; G6 strains were designated as G6e and G6f subgenotypes; the existence of genotype 10 was confirmed for the first time in Vietnam. The present study provides important information regarding the prevalence of BLV infection and genetic characteristics of BLV strains identified in Vietnam, contributing to promote the establishment of disease control and eradication strategies in Vietnam.

Serological evidence of enzootic bovine leukosis in the periurban dairy cattle production system of Al Ain, United Arab Emirates

The serostatus of enzootic bovine leukosis (EBL) was determined at three dairy farms and the Al Ain Livestock Market (AALM), within the Al Ain region of Abu Dhabi, UAE. Of the 957 bovine sera tested by ELISA, 657 were from Holstein-Friesians from three dairy farms, and 300 from Bos indicus cattle at AALM. The chi-square homogeneity test (CSHT) and the Marascuilo multiple comparison procedure (MMCP) assessed the level of significance between the proportions of EBL-seropositive cattle (ESPC) across the study farms and AALM, and between the age groups at farms 1 and 3. Overall, the proportion of ESPC was 25.7% at dairy farms and AALM, 37.0% for farms and 1.0% for AALM. Furthermore, the proportions of ESPC at farms 1, 2 and 3 were 54.7%, 0.0% and 26.3% respectively, and statistically significant differences were seen across the farm/farm and farm/AALM comparisons, and between two age groups at farms 1 and 3. The 37-72-month-old age group showed the highest proportion of ESPC. This is the first serological evidence of EBL in the UAE. As previously reported, the ESPC are comparatively higher in dairy than Bos indicus cattle. Molecular and more extensive serological studies are needed to further corroborate the present data. Meanwhile, the UAE veterinary authorities will need to formulate national EBL control policies.

Effect of bovine leukemia virus on bovine mammary epithelial cells

Bovine leukemia virus (BLV) is a retrovirus that infects cattle and is associated with an increase in secondary infections. The objective of this study was to analyze the effect of BLV infection on cell viability, apoptosis and morphology of a bovine mammary epithelial cell line (MAC-T), as well as Toll like receptors (TLR) and cytokine mRNA expression. Our findings show that BLV infection causes late syncytium formation, a decrease in cell viability, downregulation of the anti-apoptotic gene Bcl-2, and an increase in TLR9 mRNA expression. Moreover, we analyzed how this stably infected cell line respond to the exposure to Staphylococcus aureus (S. aureus), a pathogen known to cause chronic mastitis. In the presence of S. aureus, MAC-T BLV cells had decreased viability and decreased Bcl-2 and TLR2 mRNA expression. The results suggest that mammary epithelial cells infected with BLV have altered the apoptotic and immune pathways, probably affecting their response to bacteria and favoring the development of mastitis.

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.

Performance assessment of imported ELISA in the serodiagnosis of the enzootic bovine leukosis in herds of Pernambuco state, Brazil

ABSTRACT: Enzootic bovine leukosis (EBL) is an infectious disease of cosmopolitan distribution and chronic character caused by a virus of the Retroviridae family, bovine leukemia virus (BLV). The epidemiological situation of EBL in Brazil has motivated studies to improve its diagnosis, based on the recommended serological techniques: agar gel immunodiffusion (AGID) and enzyme-linked immunosorbent assay (ELISA). This study was designed to evaluate the use of imported ELISA for the detection of BLV in dairy herds raised in Pernambuco, Brazil, comparing it to AGID. Blood serum samples from 327 dairy cattle from the state of Pernambuco were tested to AGID and the imported commercial ELISA CHEKIT-Leucose-serum, produced by the IDEXX® laboratory for the diagnosis of EBL. Discarding 25 inconclusive samples from one or both tests, 302 samples were analyzed, being 24.1% positive (73/302) in the AGID and 45% (136/302) in the ELISA, which compared to the AGID, a technique considered standard, presented sensitivity of 98.6%, specificity of 72% and Kappa coefficient of 0.55. The lack of agreement in the diagnostic methods was probably due to the high sensitivity of the ELISA, which makes it possible to detect antibodies even in situations with low serum levels. Although AGID has been shown to be an efficient test so far, in more advanced stages of an EBL control and eradication program, with low prevalence rates, ELISA will present better performance, due to its higher sensitivity, avoiding the permanence of animals that spread the disease in the herds.

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.

Identification of an Atypical Enzootic Bovine Leukosis in Japan by Using a Novel Classification of Bovine Leukemia Based on Immunophenotypic Analysis

Bovine leukemia is classified into two types: enzootic bovine leukosis (EBL) and sporadic bovine leukosis (SBL). EBL is caused by infection with bovine leukemia virus (BLV), which induces persistent lymphocytosis and B-cell lymphoma in cattle after a long latent period. Although it has been demonstrated that BLV-associated lymphoma occurs predominantly in adult cattle of >3 to 5 years, suspicious cases of EBL onset in juvenile cattle were recently reported in Japan. To investigate the current status of bovine leukemia in Japan, we performed immunophenotypic analysis of samples from 50 cattle that were clinically diagnosed as having bovine leukemia. We classified the samples into five groups on the basis of the analysis and found two different types of EBL: classic EBL (cEBL), which has the familiar phenotype commonly known as EBL, and polyclonal EBL (pEBL), which exhibited neoplastic proliferation of polyclonal B cells. Moreover, there were several atypical EBL cases even in cEBL, including an early onset of EBL in juvenile cattle. A comparison of the cell marker expressions among cEBL, pEBL, and B-cell-type SBL (B-SBL) revealed characteristic patterns in B-cell leukemia, and these patterns could be clearly differentiated from those of healthy phenotypes, whereas it was difficult to discriminate between cEBL, pEBL, and B-SBL only by the expression patterns of cell markers. This study identified novel characteristics of bovine leukemia that should contribute to a better understanding of the mechanism underlying tumor development in BLV infection.

Development and evaluation of an immunochromatographic assay using a gp51 monoclonal antibody for the detection of antibodies against the bovine leukemia virus

Infection of cattle with bovine leukemia virus (BLV) has been observed and reported worldwide, including in Korea. The onsite identification of infected cattle would help decreasing and eradicating BLV infections on farms. Here, we present a new immunochromatographic assay that employs monoclonal antibodies (MAbs) for the detection of antibodies against BLV in the field. BLV envelope glycoprotein (gp)51 was expressed in E. coli, and MAbs against recombinant BLV gp51 were generated for the development of an immunochromatographic assay to detect BLV antibodies in cattle. The sensitivity and specificity of the assay were determined by comparing these results with those obtained from a standard enzyme linked immunosorbent assay (ELISA). A total of 160 bovine sera were used to evaluate the new immunochromatographic assay. Using ELISA as a reference standard, the relative specificity and sensitivity of this assay were determined to be 94.7% and 98%, respectively. Because of its high sensitivity and specificity, this BLV antibody detection assay would be suitable for the onsite identification of BLV infection in the field.

Co-infection with Mycobacterium bovis does not alter the response to bovine leukemia virus in BoLA DRB3*0902, genetically resistant cattle

High proviral load (HPL) profile in bovine leukemia virus infected animals poses increased risk of transmission, and development of HPL or low proviral load (LPL) profile may be attributed to host genetics. Genetic resistance and susceptibility has been mapped to the Major Histocompatibility Complex class II DRB3 gene (BoLA DRB3). The aim of this work was to determine the effect of Mycobacterium bovis infection on certain virological and host immunological parameters of BLV experimental infection. Twenty-six Argentinian Holstein calves carrying the resistance-associated marker allele BoLA DRB3*0902, susceptibility-associated marker allele BoLA DRB3*1501, or neutral BoLA DRB3 alleles, exposed to M. bovis were used. Twenty calves were inoculated with BLV, three were naturally infected and other three were BLV-negative. Seven from twenty six (27%) of the animals resulted positive to the PPD test. The proviral load, absolute leukocyte and lymphocyte counts, time to seroconversion, antibody titer against BLV, and viral antigen expression in vitro at various times post inoculation were determined and compared between PPD+ and PPD- animals. From a total of 23 BLV positive animals (naturally and experimentally infected), 13 (56.5%) developed HPL, and 10 (43.5%) developed LPL. None of the investigated parameters were affected by infection with M. bovis. We concluded that the ability of cattle carrying resistance-associated marker to control BLV and to progress towards a LPL phenotype was not altered by M. bovis co-infection.