Bovine Leukemia Virus in Bovine Aborted Fetuses

Abstract

We investigated the infection of Bovine Leukemia Virus (BLV) related to other pathogens [Neospora caninum, Bovine Herpesvirus-1 (BoHV-1), Bovine Viral Diarrhea Virus (BVDV), and pathogenic bacteria] in 80 bovine aborted fetuses. The materials comprised whole fetuses, fetal organs, and placenta. The BLV was diagnosed by nested-PCR (env gp51 BLV gene), the identification of viral genotypes by sequencing, and the phylogenetic analysis by neighborjoining and maximum composite likelihood methods. The other pathogens and diagnoses were, respectively: Neospora caninum (nested-PCR), BoHV-1 (nested-PCR), BVDV (PCR), Brucella spp. (isolation and identification), Leptospira spp. (PCR), aerobic bacteria [Enterobacteriaceae, Gram positive cocci, Trueperella (Arcanobacterium) pyogenes] and micro-aerophilic (Campylobacter spp., Histophilus somni, and Listeria monocytogenes) by isolation and identification. BLV fetal antibodies were identified by ELISA kit. Thirteen (16.25%) fetuses were positive by BLV nested-PCR. Phylogenetic analysis revealed BLV genotypes 1, 5, and 6, which are frequently found in cattle in Brazil, Argentina, and Uruguay. No fetuses were positive for BLV antibodies by ELISA. A single case of coinfection with BLV was found for each of the pathogens Trueperella (Arcanobacterium) pyogenes, Klebsiella spp., and Streptococcus spp. were isolated as a pure or representing the preponderance of bacteria in a pooled culture. In the 67 BLV-negative fetuses, pathogens identified were single cases of Trueperella (Arcanobacterium) pyogenes, Staphylococcus aureus, and Brucella abortus; 2 of Escherichia coli; 3 of bovine viral diarrhea virus; and 4 of Neospora caninum. No pathogens were found in 55 fetuses. The low number of BLV positive samples infected or no by other pathogens didn´t allow performing statistical analysis for understanding if there were significative differences among not infected and infected BLV fetuses. Because BLV is an immunosuppressive agent and predisposes the cow to other pathogens, its connection with Leukemia or abortions need additional studies with bigger sampling, for elucidating pathogenesis in the pregnant cow and in the fetus. The rates of BLV transplacental transmission show the necessity of prophylactic measures in Brazilian cattle herds, in order to avoid infection in utero.