 Epstein–Barr virus is important in the history of viruses for being the first virus shown to cause cancer in humans.The second half of the 20th century was the golden age of virus discovery and most of the 2,000 recognised species of animal, plant, and bacterial viruses were discovered during these years.In 1946, bovine virus diarrhea was discovered, which is still possibly the most common pathogen of cattle throughout the world and in 1957, equine arterivirus was discovered.