disease in vertebrates. Different levels of virulence may be observed depending on the strain of orthoreovirus. Species that are known to become infected with the virus include: humans, birds, cattle, monkeys, sheep, swine, baboons, and bats Replication Replication occurs in the cytoplasm of the host cell. The following lists the replication cycle of the virus from attachment to egress of the new virus particle ready to infect next host cell. Attachment Attachment occurs with the aid of the virus σ1 protein. This is a filamentous trimer protein that projects out of the outer capsid of the virus. There are two receptors for the virus on the host cell. There is the junctional adhesion molecule-A, which is a serotype-independent receptor as well as the sialic acid coreceptor. Viral proteins μ1 and σ3 are responsible for attachment by binding to the receptors. After the attachment to the receptors, entry to the host cell occurs via receptor-mediated endocytosis through the aid of clathrin coated pits. Uncoating and Entry Once inside the host cell, the virus must find a way to uncoat. The virus particles enter the cell in a structure known as an endosome (also called an endolysosome). Disassembly is a stepwise process. Uncoating requires a low pH, which is provided by the help of endocytic proteases. Acidification of the endosome removes the outer-capsid protein σ3. This removal allows membrane-penetration mediator μ1 to be exposed and attachment protein σ1 goes through a conformational change. After uncoating is completed, the active virus is released in the cytoplasm where replication of the genome and virion takes place. Replication of genome and proteins Replication of the virus takes places in the cytoplasm of the host cell. Since the genome of this virus is dsRNA, early transcription of the genome must take place inside the capsid where it is safe and will not be degraded by the host cell. dsRNA inside of a cell is a tip off to the immune system that the cell is infected with a virus, since dsRNA does not occur in the normal replication of a cell. As transcription occurs with the aid of viral polymerase, protein λ3 serves as the RNA-dependent RNA polymerase, full strands of positive sense single stranded RNA (mRNA) are synthesized from each of the dsRNA segments. Viral protein, μ2, is known to be a transcriptase cofactor during transcription. It has been determined that this protein has some