Jaagsiekte sheep retrovirus (JSRV) is a type of virus that primarily affects sheep, causing a contagious lung disease known as jaagsiekte. This disease leads to the formation of tumors in the lungs, resulting in respiratory distress and often death in infected animals. JSRV is transmitted through respiratory secretions, making it highly contagious among sheep populations. The virus is a member of the retrovirus family, which means it can integrate its genetic material into the host's DNA. Research on JSRV has provided insights into viral behavior and the mechanisms of tumor formation, contributing to a better understanding of similar diseases in other species, including humans.