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Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis, which is the most common neoplastic disease of cattle. Bovine leukocyte antigen (BoLA) is strongly involved in the subclinical progression of BLV infections. Recent studies show that the BoLA-DRB3 gene might play a direct role in controlling the number of BLV-infected peripheral B lymphocytes in vivo in Holstein cattle. However, the specific BoLA class II allele and DRB3-DQA1 haplotypes determining the BLV proviral load in Japanese Black cattle are yet to be identified. In this study, we focused on the association of BLV proviral load and polymorphism of BoLA class II in Japanese Black cattle. We genotyped 186 BLV-infected, clinically normal cattle for BoLA-DRB3 and BoLA-DQA1 using a polymerase chain reaction-sequence-based typing method. BoLA-DRB3*0902 and BoLA-DRB3*1101 were associated with a low proviral load (LPVL), and BoLA-DRB3*1601 was associated with a high proviral load (HPVL). Furthermore, BoLA-DQA1*0204 and BoLA-DQA1*10012 were related to LPVL and HPVL, respectively. Furthermore, we confirmed the correlation between the DRB3-DQA1 haplotype and BLV proviral load. Two haplotypes, namely 0902B or C (DRB3*0902-DQA1*0204) and 1101A (DRB3*1101-DQA1*10011), were associated with a low BLV proviral load, whereas one haplotype 1601B (DRB3*1601-DQA1*10012) was associated with a high BLV proviral load. We conclude that resistance is a dominant trait and susceptibility is a recessive trait. Additionally, resistant alleles were common between Japanese Black and Holstein cattle, and susceptible alleles differed. This is the first report to identify an association between the DRB3-DQA1 haplotype and variations in BLV proviral load.

Bovine leukocyte antigen (BoLA), the major histocompatibility complex of cattle, is one of the most polymorphic gene clusters. We genotyped a population of 109 Japanese Black and 39 Holstein cattle to analyze their BoLA class II haplotypes, BoLA-DRB3 locus, 5 BoLA-DQA loci, and 5 BoLA-DQB loci. We identified 26 previously reported DRB3 alleles, 22 previously reported and 3 new DQA alleles, and 24 previously reported and 6 new DQB alleles. A dendrogram was constructed based on the predicted amino acid sequences of the α1 or β1 domains encoded by BoLA-DQA or -DQB alleles, which revealed that DQA alleles were clustered into 5 loci, whereas DQB alleles could not be clearly assigned to specific DQB loci. The BoLA-DRB3-DQA-DQB haplotypes were sorted by sequential analytical processes, and 42 distinct haplotypes, including 11 previously published haplotypes and 31 novel haplotypes, were defined. Strong linkage disequilibrium was present in the BoLA genes. We also compared DRB3-DQA1 haplotype frequencies between 507 Japanese Black and 143 Holstein cattle. Thirty-nine DRB3-DQA1 haplotypes were identified, including 29 haplotypes from Japanese Black and 22 haplotypes from Holstein cattle. The majority of the haplotypes could be identified in both breeds, although several haplotypes were identified in only a single breed. This is the first report presenting a detailed study of the BoLA class II haplotype in Japanese Black and Holstein cattle in Japan.

Infections with equine herpesviruses (EHVs) are widespread in equine populations worldwide. Whereas both EHV-1 and EHV-4 produce well-documented respiratory syndromes in equids, the contribution of EHV-2 and EHV-5 to disease of the respiratory tract is still enigmatic. This study describes the detection and genetic characterization of EHVs from equids with and without clinical respiratory disease. Virus-specific PCRs were used to detect EHV-1, -2, -4 and -5. From the total of 160 equids with respiratory disease, EHV-5 was detected at the highest prevalence (23.1%), followed by EHV-2 (20.0%), EHV-4 (8.1%) and EHV-1 (7.5%). Concurrent infections with EHV-2 and EHV-5 were recorded from nine (5.2%) diseased horses. Of the total of 111 clinically healthy equids, EHV-1 and EHV-4 were never detected whereas EHV-2 and EHV-5 were found in 8 (7.2%) and 18 (16.2%) horses, respectively. A significantly higher proportion of EHV-2-infected equids was observed in the respiratory disease group (32/160, 20.0%; P = 0.005) compared to those without disease (8/111; 7.2%). EHV-2-positive equids were three times more likely to display clinical signs of respiratory disease than EHV-2-negative equids (OR 3.22, 95% CI: 1.42-7.28). For EHV-5, the observed difference was not statistically significant (P = 0.166). The phylogenetic analysis of the gB gene revealed that the Ethiopian EHV-2 and EHV-5 strains had a remarkable genetic diversity, with a nucleotide sequence identity among each other that ranged from 94.0 to 99.4% and 95.1 to 100%, respectively. Moreover, the nucleotide sequence identity of EHV-2 and EHV-5 with isolates from other countries acquired from GenBank ranged from 92.9 to 99.1% and 95.1 to 99.5%, respectively. Our results suggest that besides EHV-1 and EHV-4, EHV-2 is likely to be an important contributor either to induce or predispose equids to respiratory disease. However, more work is needed to better understand the contribution of EHV-2 in the establishment of respiratory disease.

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