By Julie Steenhuysen CHICAGO (Reuters) – Scientists across the United States say they cannot obtain samples of Ebola, complicating efforts to understand how the virus is mutating and develop new drugs, vaccines and diagnostics. The problems reflect growing caution by regulators and transport companies about handling Ebola as well as the limited resources of West African countries which are struggling to help thousands of infected citizens. Ten scientists from eight major research institutions contacted by Reuters reported they were unable to get Ebola samples in recent months. …