Detection and molecular characterization of bovine leukemia virus in Philippine cattle
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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. BLV infects cattle worldwide, imposing a severe economic impact on the dairy cattle industry. However, there are no comprehensive studies on the distribution of BLV in the Philippines, and the genetic characteristics of Philippine BLV strains are unknown. Therefore, the aim of this study was to detect BLV infections in the Philippines and determined their genetic variability. Blood samples were obtained from 1116 cattle from different farms on five Philippine islands, and BLV provirus was detected by BLV-CoCoMo-qPCR-2 and nested PCR targeting BLV long terminal repeats. Out of 1116 samples, 108 (9.7 %) and 54 (4.8 %) were positive for BLV provirus, as determined by BLV-CoCoMo-qPCR-2 and nested PCR, respectively. Of the five islands, Luzon Island showed the highest prevalence of BLV infection (23.1 %). Partial env gp51 genes from 43 samples, which were positive for BLV provirus by both methods, were sequenced for phylogenetic analysis. Phylogenetic analysis based on a 423-bp fragment of the env gene revealed that Philippine BLV strains clustered into either genotype 1 or genotype 6. Substitutions were mainly found in antigenic determinants, such as the CD4+ T-cell epitope, the CD8+ T-cell epitope, the second neutralizing domain, B and E epitopes, and these substitutions varied according to genotype. This study provides comprehensive information regarding BLV infection levels in the Philippines and documents the presence of two BLV genotypes, genotypes 1 and 6, in this population.
KeywordsBovine Leukemia Virus Proviral Load Bovine Leukemia Virus Infection Bovine Leukemia Virus Strain Neutralize Domain
We thank Drs. T. Miyasaka, M.A. Villanueva, A.J. Salces, Libertado C. Cruz and Mr. M. Ohashi, and the management and staff of the Philippine Carabao Center for kindly assisting with the large-scale sampling from many farms in the Philippines. We are grateful to the Support Unit at the Bio-material Analysis, RIKEN BSI Research Resources Center, for help with sequence analysis. This work was supported by Grants-in-Aid for Scientific Research (B and C) from the Japan Society for the Promotion of Science (JSPS), by A-STEP (Adaptable & Seamless Technology Transfer Program through Target-driven R&D) and by a grant from the Program for the Promotion of Basic and Applied Research for Innovations in Bio-oriented Industry in Japan.
Conflict of interest
The authors declare that they have no conflict of interest.
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