RECIFE, Brazil — Davi Roriz Alves de Carvalho, aged 4, rested his head on his mother’s lap, his eyes glazed and mouth slightly open. His mother, Rossandra Débora de Sà, looked down, stroked his hair tenderly and smiled.

“There is a moment of pain, of despair; that is normal,” she said, referring to when she discovered her son had microcephaly, a condition where babies are born with unusually small heads and often have associated brain damage.

“You want your child to do things and he cannot. But do not cry in front of your child, do not be unhappy in front of him. Because he already has so much trouble in his life, we must pass on joy and let him know that he is loved.”

The family lives in Pernambuco state in Brazil’s northeast, at the center of the current crisis over microcephaly. More than a quarter of the 404 confirmed and 3,670 suspected cases identified by officials in Brazil since October are here. Health officials believe the cases are linked to the spread of the tropical Zika virus, leading the World Health Organization to declare a global emergency this week.

Hundreds of mothers are now confronting the diagnosis, which can cause seizures as well as problems with vision, hearing, speech and movement. Davi and his family, though, have long been grappling with his condition. (About 150 cases were recorded in Brazil each year until the current crisis).

The failings of Brazil’s public health service — which officials here admit is unable to provide patients with sufficient doctors, equipment and infrastructure — are felt acutely by families of children with microcephaly, who typically need intensive physiotherapy, speech therapy and occupational therapy. Those are rarely, if ever, available.

“We are far from providing the high quality healthcare that Brazilians deserve,” said Dr. Jailson Correia, health secretary of the state capital Recife. Even most private health plans favored by the middle class here offer only limited coverage.

Advocates also say that prejudice against the disabled remains widespread. “When a disabled child is born in Brazil, the family is often alone,” said Claudia Werneck, a journalist who has become one of Brazil’s foremost voices on disabled rights through her NGO Escola de Gente. “And they remain alone because of the lack of support from politicians and segregation from society.”

“Microcephaly is now being presented in Brazil as this symbol of the worst thing that can happen to a child,” she added. “But there is no discussion of the rights of these children, of their future and how to make their lives better.”