A pregnant woman in Puerto Rico has become the first American whose fetus developed microcephaly because of a Zika infection acquired in the United States, the territory’s health department said on Friday.
Dr. Ana Ríus, the island’s health secretary, said the fetus, which was not carried to term, had developed a shrunken skull and calcified spots in the brain, suggesting inflammation and cell death.
The Centers for Disease Control and Prevention, which confirmed the presence of the virus in brain tissue from the fetus, released a statement saying the case “saddens and concerns us as it highlights the potential for additional cases and associated adverse pregnancy.”
The agency has estimated that 20 percent or more of the island’s 3.5 million residents will become infected with Zika this year.
The Senate is poised to vote next week on funds to combat the spread of the virus, which is expected to arrive in Southern states as summer approaches and the mosquitoes that carry the infection begin to spread north.
Administration officials had requested $1.9 billion in emergency funding and have been sharply critical of Republicans in Congress for failing to provide it. The White House has transferred $510 million intended to counter the Ebola virus to the fight against Zika.
The fetus in Puerto Rico was miscarried in the second trimester, and a local doctor, suspecting Zika-related brain damage, sent it to the C.D.C., said Dr. Johnny Rullan, a former territorial health secretary who is an adviser to the governor for the epidemic. He did not know at what week of pregnancy the miscarriage occurred, but congenital brain damage related to Zika has been detected as early as the 19th week.
The territory has had only 925 confirmed cases of Zika infection to date, but health officials assume there have been tens of thousands of unreported cases. Of the confirmed ones, 128 have involved pregnant women.
Sixteen of the infected women have given birth so far, “and the babies are progressing normally,” Dr. Ríus told El Nuevo Dia, a local paper. The children will be monitored for three years.
Dr. Rullan suspects that there have been 80,000 infections since January, assuming about 10,000 cases for each case of Guillain-Barré syndrome, a creeping paralysis caused by an autoimmune attack on the peripheral nerves triggered by a Zika infection.
As of this week, there have been eight confirmed Guillain-Barré cases since the year began.
Puerto Rico has also seen one Zika-related death in an adult. It occurred in February in a man in his 70s who recovered from Zika but succumbed to immune thrombocytopenic purpura, another type of autoimmune reaction.
There have been two other cases of microcephaly in the United States thought to be related to Zika. One involved a child born to a woman in Hawaii who had spent the early part of her pregnancy in Brazil. The other involved a pregnancy aborted by a Washington, D.C., woman who became infected on a trip through Mexico, Belize and Guatemala.
Only about a third of the roughly 15,000 pregnant women in Puerto Rico have been tested, Dr. Rullan said.
“The doctors are not being aggressive enough, and the insurance companies are not,” he said. “We had a conference, and I told them we need to do all 15,000 immediately, whether they have symptoms or not.”
He added, “I think a case of microcephaly will get people going.”