Comparison of Blood Non‐Specific Immune Parameters in Bovine Virus Diarrhoea Virus (BVDV) Persistently Infected and in Immune Heifers

Abstract

Several data from different authors show that Bovine virus diarrhoea virus (BVDV) could be a key component in multiple-etiology diseases, indeed a lower leukocytes number and their impaired functions decrease the resistance to infections. However, most of the information on the impairment of immune function during BVDV infections arise from circumstantial evidence and from experimental infection studies, and few from field data. To assess the effects of BVDV on blood cells parameters, cellular and humoral functions under field conditions, we designed a controlled study in commercial dairy herds, comparing persistent infected (PI) and healthy heifers. A total of 45 heifers were considered, the PI animals were nine, the control animals were 34, while two controls were considered as acute infected animals. The comparison of the mean values in PI calves showed a significant decrease for leukocytes and granulocytes, while platelets showed a significant increase, when compared with control animals. The total number of lymphocytes decreased not significantly in PI animals, while the proportion significantly increased. The number and proportion of monocytes was significantly reduced in PI animals, when compared with controls. The data collected on markers of cellular immunity during our study cannot be compared with the literature because there are no reference values. The presence of a persistent infection affected the cellular enzymes: NAGase, lysozyme and respiratory burst showed a large statistically significant decrease in PI animals when compared with controls. The presence of a persistent infection with BVD virus influenced blood cells number and impaired some blood cell functions. Such impairment confirms that PI animals represent a threat to the herd not only because they could spread BVDV, but also because they are more susceptible to other infectious diseases.

Comparison of bovine hematology reference intervals from 1957 to 2006

“…But, a shift to higher neutrophil counts was not universal in the survey or published results. Furthermore, a 2006 study in Italy also reported relatively low mean neutrophil counts for dairy heifers 33 …”

“…Decreased prevalence of BVD virus infection in 2001 compared with 1957 also may have affected neutrophil reference intervals. Cattle with persistent BVD infections acquired in utero may be apparently healthy, 44 yet have lower mean neutrophil counts that could skew the reference interval lower 33 . Our 2001 reference population came from herds with well‐established BVD vaccination programs, and the absence of persistently infected BVD cattle could have contributed to higher neutrophil counts.…”

Molecular findings and approaches spotlightingMycobacterium bovispersistence in cattle

“…In addition, in TB cases associated with human M. bovis infection, the HIV/AIDS pandemic may lead to a greater susceptibility of people to overt TB [39], as has been shown with the use of anti-inflammatory treatment [54]. Envisioning a similar scenario, should persistent/latent bTB in cattle be present, reactivation could be associated with changes in cell-mediated immunity in tuberculous cattle as well as with viral immunosuppression, metabolic unbalance, corticosteroids and postpartum period [32, 82, 84, 102]. Nevertheless, the association of bTB with persistent and immunosuppressive viral diseases, such as bovine viral diarrhoea and bovine leucosis, has not been described in spite of its enzootic character in dairy cattle and deserves further attention.…”

Hematology as a diagnostic tool in bovine medicine

“…Genetic selection and decreased prevalence of bovine virus diarrhea were suggested as possible reasons for higher neutrophil counts. 16 Animals persistently infected with Bovine viral diarrhea virus (BVDV) exhibit significant neutropenia, 35 thus the absence of persistently infected animals in the study might have contributed to increased neutrophil numbers. The reduced eosinophil count was assumed to be caused by decreased exposure to parasites due to modern husbandry and parasite control programs.…”