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
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A molecular model of the Zika virus. Evan Oto/Science Source hide caption
Mylene Helena Ferraira of Recife, Brazil, carries her 5-month-old son, David Henrique Ferreira, who was born with microcephaly. She's returning home after a medical visit. Mario Tama/Getty Images hide caption
While some scientists seek ways to stop the spread of Zika by mosquitoes, others have received new funding from the National Institutes of Health to track the genes and habits of the virus itself. Felipe Dana/AP hide caption
Aedes aegypti mosquitoes are displayed at an exhibition on Jan. 28 in Brazil. The mosquitoes can be carriers of the Zika virus. Several cases of the virus have spread to Puerto Rico. Mario Tama/Getty Images hide caption
Nancy Writebol, a missionary who recovered from Ebola she contracted in Liberia in 2014, told a reporter last July that she was still experiencing knee pain and hadn't fully regained her energy. Chris Keane/Getty Images hide caption
Scientists think the lone star tick (center) likely transmits Heartland disease to people. And the virus probably also circulates in deer and coyotes. iStockphoto; CDC; iStockphoto hide caption
A blood test developed by Harvard researchers checks for evidence of past infection with more than a thousand strains of virus, from about 200 virus families. The swine flu virus shown here, A/CA/4/09, rarely infects humans. C. S. Goldsmith/CDC hide caption
Augustine Goba (right) heads the laboratory at Kenema Government Hospital in Sierra Leone. He and colleagues analyzed the viral genetics in blood samples from 78 Ebola patients early in the epidemic. Stephen Gire/AP hide caption
Biologist Rob Knight, co-founder of the American Gut Project, recently moved the project to the University of California, San Diego's School of Medicine. Casey A. Cass/University of Colorado hide caption
Ecologists found signs of Ebola in a Rousettus leschenaultii fruit bat. These bats are widespread across south Asia, from India to China. Kevin Olival/EcoHealth Alliance hide caption
A woman protects her child's face in Managua, Nicaragua, as health workers fumigate for mosquitoes that carry chikungunya. The virus started spreading through Nicaragua and Mexico in the fall. Esteban Felix/AP hide caption
The dengue virus has an icosahedral shape, similar to the pattern on a soccer ball. Antibodies stop the virus by binding to its surface. Laguna Design/Science Source hide caption