BOSTON – City health officials said Monday that Boston has seen three or four possible cases of Ebola since the latest outbreak began ravaging West Africa, but they stressed that the city has had no confirmed cases. Dr. Anita Barry, head of the Infectious Disease Bureau at the Boston Public Health Commission, said all possible cases of the deadly virus turned out to be other illnesses, including malaria, typhoid fever and others typical of West Africa. But she acknowledged it is possible the city might eventually see a confirmed case of the virus, which has had a roughly 50 percent mortality rate in West Africa. “We have an international airport,” Barry said.