Enzootic bovine leukosis is a lethal neoplastic disease caused by bovine leukemia virus (BLV), belongs to family Retroviridae. The BLV proviral load (PVL) represents the quantity of BLV genome that has integrated into the host’s genome in BLV-infected cells. Bovine leukocyte antigen (BoLA) class II allelic polymorphisms are associated with PVLs in BLV-infected cattle. We sought to identify relationships between BoLA-DRB3 allelic heterozygosity and BLV PVLs among different cattle breeds. Blood samples from 598 BLV-infected cattle were quantified to determine their PVLs by real-time polymerase chain reaction. The results were confirmed by a BLV-enzyme-linked immunosorbent assay. Restriction fragment length polymorphism-polymerase chain reaction identified 22 BoLA-DRB3 alleles. Multivariate negative binomial regression modeling was used to test for associations between BLV PVLs and BoLA-DRB3 alleles. BoLA-DRB3.2*3, *7, *8, *11, *22, *24, and *28 alleles were significantly associated with low PVLs. BoLA-DRB3.2*10 was significantly associated with high PVLs. Some heterozygous allele combinations were associated with low PVLs (*3/*28, *7/*8, *8/*11, *10/*11, and *11/*16); others were associated with high PVLs (*1/*41, *10/*16, *10/*41, *16/*27, and *22/*27). Interestingly, the BoLA-DRB3.2*11 heterozygous allele was always strongly and independently associated with low PVLs. This is the first reported evidence of an association between heterozygous allelic combinations and BLV PVLs.

A cross-sectional study was used to identify and assess prevalence and phenotypic antimicrobial resistance (AMR) profiles of Escherichia coli and other enterobacteria isolated from healthy wildlife and livestock cohabiting at a 10,000 acres game ranch near Lusaka, Zambia. Purposive sampling was used to select wildlife and livestock based on similarities in behavior, grazing habits and close interactions with humans. Isolates (n = 66) from fecal samples collected between April and August 2018 (n = 84) were examined following modified protocols for bacteria isolation, biochemical identification, molecular detection, phylogenetic analysis, and antimicrobial susceptibility testing by disc diffusion method. Data were analyzed using R software, Genetyx ver.12 and Mega 6. Using Applied Profile Index 20E kit for biochemical identification, polymerase chain reaction assay and sequencing, sixty-six isolates were identified to species level, of which Escherichia coli (72.7%, 48/66), E. fergusonii (1.5%, 1/66), Shigella sonnei (22.7%, 14/66), Sh. flexinerri (1.5%, 1/66) and Enterobacteriaceae bacterium (1.5%, 1/66), and their relationships were illustrated in a phylogenetic tree. Phenotypic antimicrobial resistance or intermediate sensitivity expression to at least one antimicrobial agent was detected in 89.6% of the E. coli, and 73.3% of the Shigella isolates. The E. coli isolates exhibited the highest resistance rates to ampicillin (27%), ceftazidime (14.3%), cefotaxime (9.5%), and kanamycin (9.5%). Multidrug resistance (MDR) was detected in 18.8% of E. coli isolates while only 13.3% Shigella isolates showed MDR. The MDR was detected among isolates from impala and ostrich (wild animals in which no antimicrobial treatment was used), and in isolates from cattle, pigs, and goats (domesticated animals). This study indicates the possible transmission of drug-resistant microorganisms between animals cohabiting at the wildlife–livestock interface. It emphasizes the need for further investigation of the role of wildlife in the development and transmission of AMR, which is an issue of global concern.

Enzootic bovine leucosis (EBL) is a neoplastic disease caused by Bovine leukaemia virus (BLV) (Bartlett et al., 2014). BLV infection occurs in three possible stages: the aleukaemic stage, persistent lymphocytosis (PL) stage and EBL stage (Dequiedt et al., 1999). It is estimated that approximately 30% of BLV-infected cattle are in the PL stage, and fewer than 5% of those develop fatal B-cell lymphosarcoma (Rodríguez et al., 2011). This disease has an economic impact because it causes direct economic losses by reducing milk production and fertility, and through cattle condemnation and death (Kale et al., 2007). A great amount of efforts was directed to BLV elimination during the period 1993-2010 (EFSA Panel on Animal Health and Welfare (AHAW) et al., 2017) in the European Union (EU). As a result, most of its member states have officially declared EBL-free. In Japan, on the other hand, the nationwide survey of BLV infection from 2009 to 2011 showed that the prevalence of BLV infection in animal level was 40.9%

Most bovine leukemia virus (BLV)-infected cattle do not have clinical signs (aleukemic AL), but some develop persistent lymphocytosis (PL) and B-cell lymphosarcoma (enzootic bovine leucosis [EBL]). BLV infection is a well-known cause of chronic wasting disease, which is associated with a reduction in milk productivity and immunity in dairy cattle. However, the effect of BLV infection on beef cattle is not clear. The objective of this study was to investigate the effect of BLV infection on the productivity of slaughtered beef cattle. A total of 997 blood samples were collected from cattle in 2 slaughterhouses in Miyazaki prefecture, Japan. BLV-antibodies were tested in these cattle＇s blood samples using enzyme-linked immunosorbent assay (ELISA), to identify BLVinfected cattle. We compared blood parameters and carcass weight between BLV ELISA-positive and ELISA-negative cattle in two age groups : young (≤ 60 months) and elder (> 60 months) groups. The results showed that the proportion of ELISA-positive cattle in the young and elder groups were 22.8% and 24.9%, respectively. The number of white blood cells (WBCs) and lymphocytes in ELISA-positive cattle was significantly higher than that in ELISA-negative cattle in the young group. In addition to the number of lymphocytes, the number of monocytes and neutrophils were also significantly higher in BLV ELISA-positive cattle than in ELISAnegative cattle in the elder group. There was no significant difference in the carcass weight between ELISA-positive and ELISAnegative cattle in both groups. The results of this study suggest that BLV infection has an effect on the host immune response in beef cattle.