WASHINGTON — The Obama administration’s top health officials pitched senators Tuesday on the urgency of their $1.8 billion request to combat the Zika virus and warned against diverting funding to fight Ebola. Health and Human Services Secretary Sylvia Mathews Burwell pointed to Puerto Rico in particular, where officials fear the virus could spread rapidly. “We need to put those things in place now,” she told reporters, referring to mosquito control and other programs. Requests for additional funding face a high hurdle in the Republican-led Congress.