(Recasts with name of substance, details) MOSCOW, April 11 (Reuters) - Russia's European track champion Valery Kaikov has become the first rider to test positive for a drug the World Anti-Doping Agency (WADA) has warned has serious health risks, his Rusvelo team said on Thursday. "Kaikov had his contract terminated after testing positive for a prohibited substance," the team said in a statement. ... More...