Changes

==Pathogenesis==

==Pathogenesis==

Following entry and contact with the mucosa or the oral or nasal cavity, or the reproductive tract, BVDV replicates in epithelial cells and has a predilection for the palatine tonsil and the nasal mucosa. From here, the virus spreads to regional lymph nodes before a viraemia becomes established. Virus can be disseminated free in the blood, or associated with leukocytes, particularly lymphocytes and monocytes²⁸. Bovine viral diarrhoea virus can then gain access to many tissues, but shows a preference for lymphoid tissue, reaching its highest concentrations in the tonsil, thymus and ileum. Bone marrow²⁹ and intestinal mucosa are often infected, and the lymphoid tissue of the Peyer's patches frequently depleted. however, there is variation between strains as to which tissues are specifically infected and in generally, a wider distribution is associated with higher virulence.

 

Following entry and contact with the mucosal lining of the mouth or nose, initial replication occurs in epithelial cells with a predilection for the palatine tonsils. From here, the virus is able to spread systemically through the blood stream. Spread can occur through both free virus in the serum and virus infected leucocytes, particularly lymphocytes and monocytes. Isolation of virus from serum or leucocytes is generally possible between 3 and 10 days post infection. During systemic spread, the virus is able to gain entry to most tissues with a preference for lymphoid tissues. However, the tissues infected may vary between different virus strains.

==Diagnosis==

==Diagnosis==