Enzootic bovine leukosis and the risk to human health

Molecular investigation of possible relationships concerning bovine leukemia virus and breast cancer

Worldwide, breast cancer has an eminent morbidity and mortality rate, as it is a neoplastic disease among females. The query of the prospective danger of bovine leukemia virus (BLV) to humans is an old but exceedingly topical focus of scientific debate. The objective of the current study was to determine the possible relationship between BLV and breast cancer. A total of 2710 formalin-fixed paraffin-embedded (FFPE) breast cancer samples were selected regardless of the age, ethnicity, or municipality origin of the subjects. The presence of BLV in human breast cancer was determined through nested PCR by amplifying tax and gag genes followed by partial sequencing. Homology was confirmed by using the online BLAST Tool. BLV genes were found to be positive in 26.8% (728/2710) of the samples from breast cancer patients and 10% (10/80) of the samples without cancer (negative control). The results indicated a correlation between the presence of the BLV gene and breast cancer (odds ratio = 0.3889; confidence interval = 1,18; p = 0.0029). The current findings suggest a possible link between BLV and human breast carcinoma. Therefore, screening cattle herds and milk products is suggested to reduce the viral transmission risk to humans.

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.

Prevalence of Bovine Leukemia Virus (BLV) and Bovine Adenovirus (BAdV) genomes among air and surface samples in dairy production

We aimed to assess the occurrence of bovine viruses (bovine leukemia virus-BLV and bovine adenovirus-BAdV) at workplaces in traditional dairies and to evaluate the potential role of airborne and surface contamination in spreading of these viruses derived from raw milk. The total amount of 122 samples-including 37 air (bioaerosol), 40 surface, and 45 milk samples-were checked for the presence of BLV and BAdV genomes using RT-qPCR/qPCR method. The study showed that the viruses were present in 7 air (among them 71.4% were BLV-positive and 28.6% were BAdV-positive), 14 surface (among them 85.7% were BLV-positive and 14.3% were BAdV-positive), and 34 milk (all were BLV-positive only) samples. Statistical analysis revealed that both the air and surfaces in studied occupational environment were more frequently contaminated with BLV than with BAdV (Chi-square test: p = 0.002, Fisher's Exact test: p = 0.002). Kruskal-Wallis tests showed significant differences in BLV genome concentrations in the air (p = 0.045) as well as in BLV and BAdV genome concentrations on surfaces (p = 0.005 and p = 0.040, respectively) between studied processing areas. In units of genome copies (gc) per area, the highest concentrations of BLV and BAdV genomes in the air (9.8 × 10¹ ± 1.14 × 10² gc/m³ and 5.4 × 10¹ ± 9.1 × 10¹ gc/m³, respectively) and on surfaces (9.83 × 10² ± 7.41 × 10² gc/100cm² and 2.30 × 10² ± 3.8 × 10² gc/100cm², respectively) were observed in milk reception area. The air and surfaces of pre-production zones were also significantly more contaminated with BAdV genomes compared to production areas (Mann-Whitney test: p = 0.039 and p = 0.029, respectively). This study showed that dairy workers may be exposed to bovine viruses through the inhalation of bioaerosols and contact with contaminated surfaces. To reduce the probability of virus transmission from the raw milk to humans, efficient surface cleaning procedures degrading viral particles should be introduced and the use of personal protection equipment, especially within pre-production zones, should be required. As the raw milk may be a source of bovine viruses, the development of strategies for both the control and eradication of BLV and BAdV among cattle seems to be also urgently needed.

Genetic identification of bovine leukaemia virus

Molecular genetic research methods make it possible to evaluate the genetic diversity of bovine leukemia virus (BLV) and are the most informative approaches to its genetic identification. Molecular genetic research methods work well for the phylogenetic analysis of sequenced nucleotide DNA sequences of the provirus, as well as for the polymerase chain reaction-restriction fragment length polymorphism analysis (PCR-RFLP) according to the phylogenetic classification of the pathogen. The purpose of the research was to study the scientific and methodological approaches to the genetic identification of bovine leukemia virus, integrated into the molecular monitoring of infection of cattle with BLV genotypes. The authors used PCR-RFLP-genotyping and comparative phylogenetic analysis of aligned nucleotide sequences of the env gene fragment of the BLV provirus isolates to detect the genotypic affiliation of the cattle from twenty-one livestock farms of the Republic of Tatarstan. As a result, isolates of four out of ten BLV genotypes were found in the Tatarstani cattle, namely genotypes 1, 4, 7, and 8. The research involved a comparative analysis of 505 nucleotide sequences of a fragment of the BLV env gene, including those deposited in GenBank NCBI. The analysis confirms the inconsistency of several earlier PCR-RFLP typing strategies with the current approach in assessing the genotypic diversity by phylogenetic analysis. The improved strategy of PCR-RFLP genotyping of BLV corresponds with its modern phylogenetic classification. The strategy makes it possible to identify all the known genotypes of the viral pathogen. Its validity has been proved by in silico modelling of restrictogrammes and a phylogenetic analysis of the env gene fragment of 57 reference isolates of ten BLV genotypes that generate 57 genotype-associated combinations of diagnostically significant PCR-RFLP profiles.