Margaret Chan (left), director general of the World Health Organization, is among the dignitaries visiting a military base in Conakry, Guinea, on a tour of west African countries affected by Ebola. Also pictured: Guinean President Alpha Conde (fourth from right) and U.N. Secretary General Ban Ki-Moon (right). BINANI/AFP/Getty Images hide caption
The Zika virus is spread by mosquitoes, but it can be sexually transmitted as well. Centers for Disease Control and Prevention hide caption
Angelica Pereira feeds her daughter Luiza, who was born with microcephaly, at her mother's house in Santa Cruz do Capibaribe, Brazil. Felipe Dana/AP hide caption
Two-month-old Lara, who was born with microcephaly, is examined by a neurologist at the Pedro I hospital in Campina Grande, Paraiba state, Brazil, on Feb. 12. Felipe Dana/AP hide caption
A scientist examines mosquitoes at the lab. Walter Reed Army Institute of Research hide caption
People in Pinar del Rio, Cuba, make their way through a fumigation fog that's meant to kill the mosquito that transmits the Zika virus. Ramon Espinosa/AP hide caption
A baby born with microcephaly in Brazil is examined by a neurologist. Felipe Dana/AP hide caption
A pregnant woman gets an ultrasound to monitor for the birth defect microcephaly, in Guatemala City last month. Johan Ordonez/AFP/Getty Images hide caption
There are about 1,000 genetically engineered mosquitoes in each pot. Guilherme Trivellato of the biotech company Oxitec prepares to release them in Piracicaba, Brazil, in the hope of reducing the spread of Zika and other viruses. Catherine Osborn/for NPR hide caption
A molecular model of the Zika virus. Evan Oto/Science Source hide caption
A medical researcher prepares tests for various diseases including Zika. Arnulfo Franco/AP hide caption
A microbiologist sorts mosquitoes collected in Hutchins, Texas, to test for Zika virus. LM Otero/AP hide caption
The mosquito Aedes aegypti is a spreader of Zika virus. Jeffrey Arguedas/EPA hide caption
Marcia Andrade, an agent from Brazil's Ministry of Health, interviews Camila Alves, 22. A friend holds Alves' 2-month-old daughter. Catherine Osborn for NPR hide caption