frames (ORFs) which encode for three different proteins: P10 which promotes syncytia formation, P17, and σC involved in cell attachment. Baboon orthoreovirus The syncytia inducing capabilities of this class of orthoreoviruses combined with their association to encephalitis in baboons, distinguish them from other mammalian orthoreoviruses. While these viruses have the signature Orthoreovirus genome, they have not been found to encode for a cell attachment protein (σC), they do not encode any S-class genome segments, and are organized differently from the other species of fusogenic orthoreoviruses. The BRV genome contains 2 ORFs and contains two proteins, p15 and p16, that are not homologous to known viral or cellular proteins; however, p15 has been found to be the cell fusion protein in BRV. Avian orthoreovruses The Avian orthoreovirus has a similar structure compared to the Mammalian Orthoreovirus with the differences mainly existing in the proteins that it encodes: 10 structural proteins and 4 non-structural proteins. However, these proteins have not been studied in depth, so there is some skepticism regarding their exact functions. The pathogenesis of this virus has been studied in an attempt to determine the pathway of inducing apoptosis. Avian orthoreovirus induces apoptosis by what has been proposed as an upregulation of p53 and Bax, a mitochondria-mediated pathway. P17 has also been found to play a role in growth retardation involved in the p53 pathway. Avian Orthoreoviruses have been found to cause diseases in poultry including chronic respiratory disease, malabsorption syndrome, and arthritis representing economic losses that make this virus particularly important to study. Reptilian orthoreovirus These orthoreoviruses were first isolated in 1987 from a moribund python (Python regius) and was found to cause high levels of syncytium formation but did not cause hemagglutination in human red blood cells (RBCs). In reptiles the virus has been found widely but is not necessarily associated with any specific disease. The virus has been found to have 2 ORFs encoding for p14, a cell fusion protein and σC. RRVs belong to the fusogenic subgroup and has only recently been classified as a distinct subgroup of orthoreoviruses. Piscine orthoreovirus Also known as Piscine reovirus or PRV, was initially discovered in Atlantic salmon and subsequently in Pacific salmon and is associated with Heart and Skeletal Muscle Inflammation (HSMI) Infection and transmission Transmission of the virus is either through the fecal–oral route or through respiratory droplets. The virus is transmitted horizontally and only known to cause