Balto was the lead sled dog on the last leg of a famous, life-saving medical delivery to Nome, Alaska, in 1925. There was a serious outbreak of diphtheria in the city, and medical officials needed antitoxins to prevent the upper respiratory tract infection from spreading. The nearest doses were in Anchorage. Officials were forced to rely on dogsleds to deliver the antitoxins because the extreme cold made other modes of transport impossible. The run took seven days.