Cell-to-Cell Transmission Is the Main Mechanism Supporting Bovine Viral Diarrhea Virus Spread in Cell Culture.

After initiation of an infective cycle, spread of virus infection can occur in two fundamentally different ways: (i) viral particles can be released into the external environment and diffuse through the extracellular space until they interact with a new host cell, and (ii) virions can remain associated with infected cells, promoting the direct passage between infected and uninfected cells that is referred to as direct cell-to-cell transmission. Although evidence of cell-associated transmission has accumulated for many different viruses, the ability of members of the genus Pestivirus to use this mode of transmission has not been reported. In the present study, we used a novel recombinant virus expressing the envelope glycoprotein E2 fused to mCherry fluorescent protein to monitor the spreading of bovine viral diarrhea virus (BVDV) (the type member of the pestiviruses) infection. To demonstrate direct cell-to-cell transmission of BVDV, we developed a cell coculture system that allowed us to prove direct transmission from infected to uninfected cells in the presence of neutralizing antibodies. This mode of transmission requires cell-cell contacts and clathrin-mediated receptor-dependent endocytosis. Notably, it overcomes antibody blocking of the BVDV receptor CD46, indicating that cell-to-cell transmission of the virus involves the engagement of coreceptors on the target cell. BVDV causes one of the most economically important viral infections for the cattle industry. The virus is able to cross the placenta and infect the fetus, leading to the birth of persistently infected animals, which are reservoirs for the spread of BVDV. The occurrence of persistent infection has hampered the efficacy of vaccination because it requires eliciting levels of protection close to sterilizing immunity to prevent fetal infections. While vaccination prevents disease, BVDV can be detected if animals with neutralizing antibodies are challenged with the virus. Virus cell-to-cell transmission allows the virus to overcome barriers to free virus dissemination, such as antibodies or epithelial barriers. Here we show that BVDV exploits cell-cell contacts to propagate infection in a process that is resistant to antibody neutralization. Our results provide new insights into the mechanisms underlying the pathogenesis of BVDV infection and can aid in the design of effective control strategies.