Bovine Leukemia Virus Infection in Neonatal Calves. Risk Factors and Control Measures

Abstract

Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis (EBL). Although efficient eradication programs have been successfully implemented in most European countries and Oceania, BLV infection rates are still high worldwide. BLV naturally infects cattle, inducing a persistent infection with diverse clinical outcomes. The virus infects lymphocytes and integrates a DNA intermediate as a provirus into the genome of the cells. Therefore, exposure to biological fluids contaminated with infected lymphocytes potentially spreads the virus. Vertical transmission may occur in utero or during delivery, and about 10% of calves born to BLV-infected dams are already infected at birth. Most frequently, transmission from dams to their offspring occurs through the ingestion of infected colostrum or milk. Therefore, although EBL is not a disease specific to the neonatal period, during this period the calves are at special risk of becoming infected, especially in dairy farms, where they ingest colostrum and/or raw milk either naturally or artificially. Calves infected during the first week of life could play an active role in early propagation of BLV to susceptible animals. This review discusses the main factors that contribute to neonatal BLV infection in dairy herds, as well as different approaches and management practices that could be implemented to reduce the risk of BLV transmission during this period, aiming to decrease BLV infection in dairy herds.

Polymorphism of Haplotypes of Bovine Leukemia Virus

“…It is noteworthy that only 25% of all selected infected animals did not show clinical signs of leukemia expressed by the leukocyte formula. Earlier studies show that the latent leukemia is characteristic for at least 70% of the carriers [2,35,36]. Moreover, both BLV haplotypes are more aggressive in this study, causing a large proportion of clinical cases of leukemia, even in comparison with the results of typing of animals from other farms in the Novosibirsk Region [31].…”

Molecular Epidemiological and Serological Studies of Bovine Leukemia Virus in Taiwan Dairy Cattle

“…As BLV activities have been detected in saliva, milk, and the nasal secretions of cattle (5, 31), in these circumstances, without necessary precautions being taken during cattle handling, processing, and routine husbandry, the iatrogenic transmission would not be avoided. On the other hand, although the possibility of vertical transmission is far less than horizontal, when BLV DNA intermediate as a provirus was integrated into the chromosome of lymphocytes or frozen semen samples (32–35), the offspring might vertically acquire the BLV genome from a parent via in utero route or artificial insemination procedure, respectively. Hence, effective BLV surveillance, segregation of BLV-positive cows, and good management practices are essential to minimize BLV transmission.…”

Epizootic situation with bovine leukemia in the Central Federal District of the Russian Federation in 2012–2016

“…In recent years, the scope of scientific research has expanded significantly and new data have been obtained on the organization of preventive and antiepizootic measures that allow the effective use of a system of therapeutic antileukemia measures depending on the degree of damage to the dysfunctional herd, including through the replacement of cattle breeds with leukemia-resistant [7,13,[24][25][26][27]. However, the existing systems of antiepizootic measures are far from perfect and require scientific and industrial development, taking into account the regional epizootological features of bovine leukemia.…”