What is the common name for livestock diseases caused by viruses?

The common name for livestock diseases caused by viruses is indeed viral infections. This term specifically refers to diseases that result from the intrusion of viruses into the host organism, leading to a variety of clinical signs based on the specific virus and the type of livestock affected. Viral infections can range from mild to severe and can significantly impact animal health and productivity.

Other options don't accurately describe viral diseases; infectious diseases is a broader category that encompasses various pathogens, including bacteria and parasites, as well as viruses. Parasitic infections refer specifically to diseases caused by parasites, while bacterial infections are caused by bacteria. Thus, "viral infections" is the precise term that captures the nature of diseases stemming from viruses, making it the correct answer in this context.