In this Sept. 27, 2016 photo, Solange Ferreira holds her son Jose Wesley Campos as family friend Sandra Souza, right, holds his nasogastric feeding tube during his 1-year birthday party at his home in Bonito, Pernambuco state, Brazil. Learning how to feed is the Jose's latest struggle as medical problems mount for him and many other infants born with small heads to mothers infected with the Zika virus in Brazil. (AP Photo/Felipe Dana)

Two weeks shy of his first birthday, doctors began feeding Jose Wesley Campos through a nose tube because swallowing problems had left him dangerously underweight.

Learning how to feed is the baby's latest struggle as medical mount for him and many other infants born with small heads to mothers infected with the Zika virus in Brazil.

"It hurts me to see him like this. I didn't want this for him," said Jose's mother, Solange Ferreira, breaking into tears as she cradled her son.

A year after a spike in the number of newborns with the defect known as microcephaly, doctors and researchers have seen many of the babies develop swallowing difficulties, epileptic seizures and vision and hearing problems.

While more study is needed, the conditions appear to be causing more severe problems in these infants than in patients born with small heads because of the other infections known to cause microcephaly, such as German measles and herpes. The problems are so particular that doctors are now calling the condition congenital Zika syndrome.

"We are seeing a lot of seizures. And now they are having many problems eating, so a lot of these children start using feeding tubes," said Dr. Vanessa Van der Linden, a pediatric neurologist in Recife who was one of the first doctors to suspect that Zika caused microcephaly.

In this Sept. 27, 2016 photo, babies born with microcephaly Alexandro Julio, center, and Pedro Henrique, wait for their physical therapy session at the UPAE hospital in Caruaru, Pernambuco state, Brazil. A year after a spike in the number of newborns with the defect known as microcephaly, doctors and researchers have seen many of the babies develop swallowing difficulties, epileptic seizures and vision and hearing problems. (AP Photo/Felipe Dana)

Zika, mainly transmitted by mosquito, was not known to cause birth defects until a large outbreak swept through northeastern states in Latin America's largest nation, setting off alarm worldwide. Numerous studies confirmed the link.

Seven percent of the babies with microcephaly that Van der Linden and her team have treated were also born with arm and leg deformities that had not previously been linked to other causes of microcephaly, she said.

To complicate matters, there are babies whose heads were normal at birth but stopped growing proportionally months later. Other infants infected with the virus in the womb did not have microcephaly but developed different problems, such as a patient of Van der Linden's who started having difficulties moving his left hand.

"We may not even know about the ones with slight problems out there," Van der Linden said. "We are writing the history of this disease."

In this Sept. 26, 2016 photo, Erildo Jose and his wife Iraci Beatriz, whose granddaughter Luiza was born with microcephaly, ride their motorcycle near home in Santa Cruz do Capibaribe, where many cases of Zika where reported in Pernambuco state, Brazil. Zika, mainly transmitted by mosquito, was not known to cause birth defects until a large outbreak swept through northeastern states in Latin America's largest nation, setting off alarm worldwide. Numerous studies confirmed the link. (AP Photo/Felipe Dana)

On a recent day, Jose laid on a blue mat wearing just brown moccasins and a diaper, his bony chest pressed by a respiratory therapist helping him clear congested airways.

Jose, who has been visited by The Associated Press three times in the last year, is like a newborn. He is slow to follow objects with his crossed eyes. His head is unsteady when he tries to hold it up, and he weighs less than 13 pounds, far below the 22 pounds that is average for a baby his age.

Breathing problems make his cries sound like gargling, and his legs stiffen when he is picked up. To see, he must wear tiny blue-rimmed glasses, which makes him fussy.

Arthur Conceicao, who recently turned 1, has seizures every day despite taking medication for epilepsy. He also started taking high-calorie formula through a tube after he appeared to choke during meals.

In this Sept. 30, 2016 photo, 1-year-old Jose Wesley Campos, who was born with microcephaly, cries during his physical therapy session at the AACD rehabilitation center in Recife, Brazil. Jose is like a newborn. He is slow to follow objects with his crossed eyes. His head is unsteady when he tries to hold it up, and he weighs less than 13 pounds, far below the 22 pounds that is average for a baby his age. (AP Photo/Felipe Dana)

"It's every mom's dream to see their child open his mouth and eat well," said his mother, Rozilene Ferreira, adding that each day seems to bring new problems.

Studies are underway to determine if the timing of the infection during pregnancy affects the severity of the abnormalities, said Ricardo Ximenes, a researcher at the Fiocruz Institute in Recife.

Also, three groups of babies whose mothers were infected with Zika are being followed for a study funded by the U.S. National Institutes of Health. The groups include infants born with microcephaly, some born with normal-sized heads found to have brain damage or other physical problems and babies who have not had any symptoms or developmental delays.

At birth, Bernardo Oliveira's head measured more than 13 inches, well within the average range. His mother, Barbara Ferreira, thought her child was spared from the virus that had infected her during pregnancy and stricken many newborns in maternity wards in her hometown of Caruaru, a small city 80 miles west of Recife.

In this Sept. 26, 2016 photo, Angelica Pereira, center right, chats with her sister and sister's boyfriend outside her home as her infant daughter Luiza, who was born with microcephaly, sleeps in Santa Cruz do Capibaribe, Pernambuco state, Brazil. A year after a spike in the number of newborns with the defect known as microcephaly, doctors and researchers have seen many of the babies develop swallowing difficulties, epileptic seizures and vision and hearing problems. (AP Photo/Felipe Dana)

But Bernardo cried nonstop. The pediatrician told Ferreira that her baby was likely colicky and would get better by the third month. Instead, the crying got worse, so Ferreira took him to a government-funded event where neurologists were seeing patients with suspected .

"At the end of the second month, beginning of the third, his head stopped growing," Ferreira said. "Bernardo was afflicted by the Zika virus after all. I was in despair."

In Brazil, the government has reported 2,001 cases of microcephaly or other brain malformations in the last year. So far, only 343 have been confirmed by tests to have been caused by Zika, but the Health Ministry argues that the rest are most likely caused by the virus.

Health Minister Ricardo Barros said there was a drop of 85 percent in microcephaly cases in August and September compared to those months last year, when the first births started worrying pediatricians. He credited growing awareness of the virus and government attempts to combat mosquitoes through spraying campaigns.

In this Sept. 27, 2016 photo, relatives and hospital staff pose for a photo with Jose Wesley Campos during his 1-year birthday party at home in Bonito, Pernambuco state, Brazil. Learning how to feed is Jose's latest struggle as medical problems mount for him and many other infants born with small heads to mothers infected with the Zika virus in Brazil. (AP Photo/Felipe Dana)

Despite all the problems, some infants with the syndrome are showing signs of progress.

On a recent evening, 11-month-old Joao Miguel Silva Nunes pulled himself up in his playpen and played peek-a-boo with his mother, Rosileide da Silva.

"He is my source of pride," Silva said. "He makes me feel that things are working out."

  • In this Oct. 1, 2016 photo, Daniele Ferreira dos Santos and her son Juan Pedro, right, sit next to Heloisa Dias who feeds her grandson Arthur Conceicao during his one-year birthday party in Recife, Pernambuco state, Brazil. Arthur, who was born with microcephaly, has started taking high-calorie formula through a tube after he appeared to choke during meals. (AP Photo/Felipe Dana)

  • This Sept. 27, 2016 photo shows Lucas Matheus, who was born with microcephaly, during his physical therapy session at the UPAE hospital in Caruaru, Pernambuco state, Brazil. In Brazil, the government has reported 1,949 cases of microcephaly or other brain malformations in the last year. (AP Photo/Felipe Dana)

  • In this Sept. 27, 2016 photo, physical therapist Camilla Costa, left, and speech therapist Amora Marins apply Kinesio Tape on Luiza as Victoria Leticia, right, holds her son Lucas Matheus, during a physical therapy session for babies born with microcephaly at the UPAE hospital in Caruaru, Pernambuco state, Brazil. A year after a spike in the number of newborns with microcephaly, doctors and researchers have seen many of the babies develop swallowing difficulties, epileptic seizures and vision and hearing problems. (AP Photo/Felipe Dana)

  • In this Sept. 28, 2016 photo, 1-year-old Jose Wesley Campos, who was born with microcephaly, cries during a physical therapy session at the AACD rehabilitation center in Recife, Brazil. Breathing problems make his cries sound like gargling, and his legs stiffen when he is picked up. (AP Photo/Felipe Dana)

  • In this Sept. 28, 2016 photo, Helena Melo, who was born with microcephaly, balances on a ball during a physical therapy session at the AACD rehabilitation center in Recife, Brazil. Melo, 11 months old, travels more than two hours to Recife for therapy sessions three times a week. (AP Photo/Felipe Dana)

  • This Sept. 28, 2016 photo shows 1-year-old Arthur Conceicao, who was born with microcephaly, during his swimming pool physical therapy session at AACD rehabilitation center in Recife, Brazil. While scientists probe how Zika attacks fetuses in the womb, babies like Arthur born with brain damage caused by the virus are suffering numerous health problems such as trouble swallowing, worsening epileptic seizures and difficulty breathing. (AP Photo/Felipe Dana)

  • This Sept. 26, 2016 photo shows Lucas, 11, collecting water from a polluted well in a village near Caruaru, Pernambuco state, Brazil. Lucas' family uses the water for bathing, and for horses and donkeys to drink. One of the main reasons this region was so affected by Zika is the fact that they don't have water, so they collect and store water everywhere, creating a perfect breading site for mosquitoes, which carry the virus. (AP Photo/Felipe Dana)

  • This Oct. 1, 2016 photo shows Daniele Ferreira looks over Arthur Conceicao, counter clockwise beginning from back left, sleeping at his one-year birthday party, next to Alice, Enzo, and Mateus, all born with microcephaly, in Recife, Pernambuco state, Brazil. Away from medical facilities, many of the mothers of babies afflicted with microcephaly, get together and try to keep a semblance of normalcy by celebrating milestones, like first birthdays. (AP Photo/Felipe Dana)

  • In this Oct. 1, 2016 photo, Tatiane holds her nephew Arthur Conceicao, who was born with microcephaly, during his one-year birthday party in Recife, Pernambuco state, Brazil. Health Minister Ricardo Barros said there was a drop of 85 percent in microcephaly cases in August and September compared to those months last year, when the first births started worrying pediatricians. He credited growing awareness of the virus and government attempts to combat mosquitoes through spraying campaigns. (AP Photo/Felipe Dana)

  • In this Oct. 1, 2016 photo, Rozilene Ferreira and her husband Elias Rodrigo celebrate the one-year birthday of their son Arthur, who was born with microcephaly, in Recife, Pernambuco state, Brazil. Arthur has started taking high-calorie formula through a tube after he appeared to choke during meals. "It's every mom's dream to see their child open his mouth and eat well," said his mother, adding that each day seems to bring new problems. (AP Photo/Felipe Dana)

  • In this Oct. 1, 2016 photo, mothers hold their babies, who have microcephaly, from left, Alice Vitoria, Juan Pedro and Joao Guilherme, during Arthur's one-year birthday party, at his home in Recife, Pernambuco state, Brazil. Away from medical facilities, many of the mothers of babies born with microcephaly get together and try to keep a semblance of normalcy by celebrating milestones, like first birthdays. (AP Photo/Felipe Dana)

  • In this Oct. 1, 2016 photo, Vanessa dos Santos holds her son Enzo, who was born with microcephaly, as she walks home with her daughter Lorena in Recife, Pernambuco state, Brazil. Studies are underway to determine if the timing of mothers who were infected with Zika during pregnancy affects the severity of the abnormalities, said Ricardo Ximenes, a researcher at the Fiocruz Institute in Recife. (AP Photo/Felipe Dana)

  • In this Sept. 26, 2016 photo, Angelica Pereira holds her daughter Luiza, who was born with microcephaly, as her husband Dejailson Arruda stands by at their home in Santa Cruz do Capibaribe, Pernambuco state, Brazil. Pereira says it's a victory just for her daughter Luiza to reach her first birthday. Despite Luiza's suffering from daily seizures and breathing problems, Pereira is hopeful her health and motor skills will improve with time. (AP Photo/Felipe Dana)

  • This Sept. 26, 2016 photo shows Luiza, who was born with microcephaly and is almost 1-year-old, sleeping under a mosquito net in her home in Santa Cruz do Capibaribe, Pernambuco state, Brazil. As they reach their first birthdays, babies stricken by Zika in Brazil are developing a host of health problems. The disease is mainly transmitted by mosquito and was not known to cause birth defects until a large outbreak swept through northeastern states in Latin America's largest nation.(AP Photo/Felipe Dana)

  • In this Sept. 26, 2016 photo, Dejailson Arruda holds his daughter Luiza, who was born with microcephaly when her mother was infected with the Zika virus, at their home in Santa Cruz do Capibaribe, Pernambuco state, Brazil. While more study is needed, swallowing difficulties, epileptic seizures and vision and hearing problems appear to be causing more severe problems in these infants than in patients born with small heads because of the other infections known to cause microcephaly, such as German measles and herpes. (AP Photo/Felipe Dana)

  • In this Sept. 27, 2016 photo, the sun rises in Santa Cruz do Capibaribe, where many cases of Zika were reported in Pernambuco state, Brazil. As they reach their first birthdays, babies stricken by Zika in Brazil are developing a host of health problems. The disease is mainly transmitted by mosquito and was not known to cause birth defects until a large outbreak swept through northeastern states in Latin America's largest nation. (AP Photo/Felipe Dana)

  • In this Sept. 29, 2016 photo, Aedes aegypti mosquitoes, responsible for transmitting Zika, sit in a petri dish at the Fiocruz Institute in Recife, Brazil. Fiocruz Institute in Pernambuco collects mosquitoes from many areas around the state to test eradication efforts of the federal government such as one in which they sterilize male mosquitoes for them not to reproduce. (AP Photo/Felipe Dana)