RECIFE, Brazil — So many distraught mothers stream into the infant ward clutching babies with abnormally small heads that the receptionist sends them outside, to see if they can find a chair to wait under the mango tree.

“There’s shade there, at least,” said Maria Helena Lopes, 66, as she greeted one young mother after another. “We’ll call you when we’re ready.”

Roziline Ferreira took three buses to get here, grasping her 3-month-old son, Arthur, all the way. Tears swelled as she looked at him, recalling how the symptoms of the Zika virus had struck her during the second month of her pregnancy. How would she ever be able to care for him, she wondered? What kind of life would he have?

“It gets me angry when someone on the bus looks at Arthur and asks, ‘What’s wrong with his head?’” Ms. Ferreira said. “I tell them, ‘Nothing’s wrong, he’s just different.’ But then I think to myself, ‘Yes, something’s wrong. My son will never be like the other boys.’ ”