Abstract

MARIN A, Carlos et al. Absence of Vertical Transmission of the Bovine Leukemia Virus in Calves Born of Cows Positive to the Infection. Rev. Fac. Cienc. Vet. [online]. 2017, vol.58, n.2, pp.45-52. ISSN 0258-6576.

Bovine leukemia virus (BLV) is an oncogenic transmissible disease caused by the bovine leukemia virus, a type C delta-retrovirus, which provokes a subclinic infection in adult cattle and a type of proliferative pseudoleukemia (persistent lymphocytosis). Furthermore, 1 to 5% of the animals develop a multicentric tumoral form. Despite advances in the knowledge of this pathology, epidemiological controversies persist, particularly the transplacental transmission. To clarify them, 43 BLV-serological positive and 48 BLV-serological negative pregnant cows, detected by the agar-gel immune diffusion test (AGID) were selected. Parturition was induced with prostaglandin-F_2α to control calves birth and to avoid contact with BLV from cow’s colostrum and milk. At birth, blood was collected for serology. A total of 91 calves were studied and randomly assigned to three groups: Group I: 27 calves born to serum positive cows that were not allowed to ingest milk or colostrum; Group II: 16 calves born to serum positive cows, which were only fed colostrum; Group III: 48 calves born to serum negative cows, which were fed colostrum and milk. A sterile and frozen colostrum pool was prepared from serum negative cows. All groups were isolated for 4 months, fed with dairy substitutes and grazed in tick-free, with a strict fly control. At the end of the first year of the trial, all calves from the three groups were negative to the AGID test. In the second year, of the total calves, 83 (95.6%) remained negative results to the IDAG and 8 (4.4%) showed positive serum conversion to BLV. Of these, 4 calves (2.2%) belonged to group II and the other 4 (2.2%) to group III. The time of appearance of BLV infection in infected calves was 15±4 months. It is concluded that BLV vertical transmission did not occur and colostrum ingestion does not represent a risk of infection.

Keywords : Retrovirus; bovine enzootic leukosis; BLV; persistent lymphocytosis; colostrum; vertical transmission; calves.

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