The loss of the Izagirre brothers, who went down with the illness on Sunday, constitutes a blow to Movistar's hope for the race. Movistar have Nairo Quintana as their leader for the six day Basque race, which Quintana won in 2013.
Ion Izagirre was in strong form, taking the GP Miguel Indurain one-day race on Saturday in a spectacular two-up hilly duel against Team Sky's Sergio Henao. A winner of the Tour de Pologne in 2015, Izagirre had finished third in the Vuelta al País Vasco last year and had recently finished fifth in Paris-Nice.
"Both of them have gastroenteritis," team doctor Jesus Hoyos told Cyclingnews at the start of the opening stage of the Vuelta al Pais Vasco. "Both of them went home after the GP Indurain, the strange thing is that they hadn't eaten together since Friday evening and the rest of the team from that race feel absolutely fine, including the staff. It's baffling."