A member of the Syrian government forces watches during an evacuation of Syrian rebel fighters and civilians from a opposition-held area of Aleppo on Friday. George Ourfalia/AFP/Getty Images hide caption
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A mother holds her baby, who has microcephaly, in Recife, Brazil. Mario Tama/Getty Images hide caption
One of these candidates will be the next head of WHO. Top row from left: Tedros Adhanom Ghebreyesus, Flavia Bustreo, David Nabarro. Bottom row from left: Miklós Szócska, Sania Nishtar, Philippe Douste-Blazy. Getty Images, AP and WHO hide caption
A 2014 photo shows a tuberculosis patient preparing to take his medication at Lal Bahadur Shastri Government Hospital in Varanasi, India. Rajesh Kumar Singh/AP hide caption
A wrecked police motorcycle lays on the scene after a suspected drunk driver crashed during the Oklahoma State University homecoming parade in Stillwater, Okla. J Pat Carter/Getty Images hide caption
A government worker sprays mosquito insecticide fog in Kuala Lumpur, Malaysia, earlier this month to block the spread of Zika. The U.S. CDC advises pregnant women to reconsider plans to travel to Malaysia and 10 other countries because of the virus. Joshua Paul/AP hide caption
Chinashama Sainvilus is one of three babies born with microcephaly at the Mirebalais Hospital in Haiti in July. Jason Beaubien/NPR hide caption
A microscope image, magnified 600 times, of the bacteria that cause the sexually transmitted disease gonorrhea. BSIP/UIG via Getty Images hide caption
A Syrian Red Crescent team works to evacuate the conjoined twins to a hospital in Damascus on Friday. Courtesy of the Syrian American Medical Society hide caption
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
World Health Organization head Dr. Margaret Chan delivering a speech in March of this year at a summit in Lyon, France. Francois Mori/AP hide caption
A baby born with microcephaly in Brazil is examined by a neurologist. Felipe Dana/AP hide caption
Health workers fumigate to wipe out mosquitoes in Recife, Brazil. Mario Tama/Getty Images hide caption
WHO: Birth Defect Linked To Zika Virus Is 'Public Health Emergency'
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
A unidentified family member (right) of a 10-year-old boy that contracted Ebola has her temperature measured by a health worker outside an Ebola clinic on the outskirts of Monrovia, Liberia, on Nov. 20. Liberia, Guinea and Sierra Leone have now gone 42 days without a single reported case of Ebola. Abbas Dulleh /AP hide caption