Mr. Alves added that he expected the Zika outbreak to ease to the point that the Olympics here in August would not be affected.Yet others in Brazil applauded the C.D.C.’s alert, pointing to the country’s struggle not just with Zika, a virus with origins in Uganda that is thought to have made the leap to Brazil in 2014, but also with two other mosquito-borne viruses, dengue and chikungunya. Last year, Brazil registered more than 1.6 million cases of dengue, a virus causing fever and joint pain, with 863 people dying from the disease.