Serological survey of Bovine leukemia virus infection in dairy cattle herds in the Central-Eastern mesoregion of Paraná state, southern Brazil

Abstract

Bovine leukemia virus (BLV) is an oncogenic retrovirus belonging to the subfamily Orthoretrovirinae and genus Deltaretrovirus. It is the etiological agent of enzootic bovine leukosis, an infectious disease that affects cow longevity and milk production, potentially leading to economic losses. Serological surveys provide valuable information on BLV circulation in dairy cattle herds. This study evaluated the serological profile of BLV infection in high-yield dairy cattle herds in the Central-Eastern mesoregion of Paraná State, Southern Brazil. Whole-blood samples were collected from 628 lactating cows in 43 dairy cattle herds between October 2019 and January 2020. Serum samples were stored at –80 °C until processing. Serological tests were performed using a commercially available ELISA kit to detect antibodies against glycoprotein 51 (gp51) in the BLV envelope. Herds were considered positive when at least one cow tested positive for anti-gp51 antibodies. The data obtained were categorized by type of management (intensive and semi-intensive) and the number of lactating cows per herd (<100, 100–200, and >200) and subjected to statistical analyses using chi-square and odds ratio tests at a 95% confidence level. Notably, all 43 (100.0%) evaluated herds were seropositive for BLV, with 10 herds (23.3%) showing 100% positivity in the evaluated cows. Of the sampled cows, 82% (515/628) were seropositive for BLV. The results of the statistical analyses for both factors were compared with the frequency of seropositive cows. Herds with 100–200 lactating cows exhibited a higher chance of being positive than those with <100 or >200 lactating cows. Moreover, herds under intensive management practices showed a 1.87-times greater chance of becoming infected with BLV than those under semi-intensive management. The serological survey results indicated that BLV infection is endemic in the Central-Eastern mesoregion of Paraná State. Enzootic bovine leukosis is a clinically silent retroviral disease, with overt clinical manifestations occurring only sporadically. Nevertheless, BLV infection is associated with reduced animal productivity and significant economic losses. Therefore, only coordinated actions to raise awareness among all stakeholders in the dairy production chain regarding the epidemiological importance of BLV and its routes of transmission will help to reduce the prevalence of seropositive animals and herds in endemic regions.