Changes in leukocyte and erythrocyte blood profile and parameters under a combined Anaplasma marginale and bovine leukemia virus infection in cattle

The global spread of infectious diseases and large-scale import of cattle genetic resources lead to necessity of developing screening methods that estimate the danger of co-infection with different pathogens and its impact on animal adaptiveness. In this regard here we analyzed the variability of erythrocyte and leukocyte characteristics in dairy Black-and-White holsteinized cattle naturally infected by Anaplasma marginale, the causative agent of bovine anaplasmosis, and bovine leukemia virus (BLV). The results showed that BLV infection of cattle did not facilitate the cross-infection with A. marginale in cattle since more than half of A. marginale-free animals were BLV-infected, and about one-third cows were characterized by leukocytosis. Except an increased number of leukocytes and lymphocytes due to retroviral infection, A. marginale-free animals were characterized only by the absence of statistically significant correlation between the counts of erythrocytes and neutrophils as compared to A. marginale-infected cows, which may point at the activation of nonspecific defense mechanisms in A. marginale-infected animals. Testing animals for BLV infection by agar gel immunodiffusion (AGID) and polymerase chain reaction (PCR) assays revealed the proviral DNA integration in one AGID-negative cow, whereas in seven out of thirty four AGID-positive cows the proviral DNA was absent. Leukocytosis (> 20½109 blood leukocytes per liter) was revealed only in six AGID- and PCR-positive cows. The only common feature of BLV-infected animals with moderate and severe leukocytosis was thrombocytosis, as well as disruption of correlational relationships between the number of agranulocytes and granulocytes in peripheral blood. The detected disruption of the network relationships between different leukocyte populations reflects deep changes in the immune system functioning induced by retroviral infection. We observed a deficiency of neutrophils in cows with leukocytosis, which is in consistency with the data on neutropenia in milk of BLV-infected cows with leucosis (M. Nishiike et al., 2016). Considering the absence of BLV diagnostic tests that are able to reliably exclude the false-positive or false-negative results, it seems that the most effective approach for herd sanitation may consist in a simultaneous quantification of viral load (the number of BLV RNA in peripheral blood cells) and estimation of leukocytosis severity.