Brazil is enduring an extraordinary outbreak of microcephaly, a rare birth defect that results in infants being born with abnormally small heads and brains. Since last fall, more than 4,000 suspected cases have been reported, and authorities have blamed an unusual virus, Zika, carried by mosquitos.
But now it appears that a number of those cases may not in fact be microcephaly, or not linked to Zika.
On Wednesday, Brazil’s Ministry of Health said 4,180 cases of Zika-related microcephaly had been reported since October. The country is trying to find out which cases it could actually confirm from notifications provided by doctors — a slow and complicated process as the information is compiled and checked by health secretariats in 26 states and one federal district spread across South America’s biggest country.
After experts scrutinized 732 of the cases they found that more than half either weren’t microcephaly, or weren’t related to Zika.
Just 270 were confirmed as microcephaly that appears to be linked to Zika or other infectious diseases, according to the latest ministry bulletin.
It’s not yet clear whether the same pattern will emerge from the rest of the 3,448 cases that Brazil has to examine. And health experts say the huge number of cases is still very worrisome — as is the rapid spread of Zika through the Americas. (Brazil reported just 147 cases of microcephaly in 2014).
Microcephaly causes babies to be born with abnormally small heads, and can cause motor and learning difficulties, among other problems. The condition can also be caused by genetic factors or drug or alcohol abuse during pregnancy.
Some scientists said the new data suggest that Brazil will have fewer cases of Zika-related microcephaly than originally feared. The country may have over-counted microcephaly cases because it initially asked doctors to report all births of babies with a head circumference of 33 centimeters or less — but some of those were simply children with normally small heads.
“It is possible that the number of cases of microcephaly with suspected relationship to Zika will be much less,” said Esper Kallas, an infectious diseases specialist and professor of medicine at the University of São Paulo. “I think it will be less than a third” of the possible cases that have been reported, he said.
Kallas also said the outbreak had made Brazil realize that microcephaly unrelated to Zika was more common than authorities realized in the past.
Other specialists, though, were wary of the new data, questioning the methodology that was being used. They noted that authorities in one of the badly affected areas, the northeastern state of Bahia, have used relatively cheaper transcranial ultrasound imaging — rather than CT brain imaging scans — to try to confirm and discard cases of microcephaly.
The more inexpensive test might not spot milder cases of the condition, said Ganeshwaran Mochida, a pediatric neurologist and researcher at Boston Children’s Hospital. “There could be some cases mistakenly discarded due to not enough sensitivity,” he said.
Zika was first confirmed in Brazil in May last year, and has spread rapidly in the hemisphere, reaching 23 countries and territories. Its explosive growth has alarmed health professionals who worry about the suspected linkage to microcephaly and a rare nervous system syndrome known as Guillain-Barré that can lead to paralysis.
The World Health Organization has convened an emergency meeting to explore ways of stopping the transmission of Zika for Monday.
“The level of alarm is extremely high, as is the level of uncertainty," Margaret Chan, the director-general of the World Health Organization, said during a briefing of member countries on Thursday in Geneva.
In October, when the Brazilian government began requiring doctors to report suspected cases, they were instructed to notify the Health Ministry if the circumference of a newborn baby’s head was 33 centimeters (about 13 inches) or less.
In December, the ministry reduced the figure to 32 centimeters (12.6 inches) or less, roughly in line with WHO guidelines. The ministry said some babies with the larger measurement were later found to be healthy, although a ministry spokeswoman said she did not have exact figures on how many.
Some officials at the state level say they also believe that many of the cases of possible Zika-linked microcephaly will also be found to be something else.
In northeastern Pernambuco state, one of the areas hardest-hit by the health crisis, authorities estimate that less than half of the 1,373 reported suspect cases are likely to be microcephaly linked to Zika. Some children just have small heads, others could have microcephaly caused by genetic factors, or alcohol or drug abuse by the mother during pregnancy -- cases which do not show the same type of brain malformation.
So far, the state has investigated 248 cases, using CT brain imaging scans. A total of 138 cases were confirmed as probable Zika-related microcephaly, and 110 were discarded, local authorities said.
“There are many normal children who were included [in the original count]. This generates a lot of anguish for the families, for the general population,” said Vanessa van der Linden, a pediatric neurologist in Recife. Van der Linden was the first doctor to identify the microcephaly outbreak in Brazil.
Mochida from Boston Children's Hospital said that using standard U.S. growth charts, the 33- centimeter guide would put 10 percent of American newborns in the category of suspected microcephaly — clearly way too high a percentage.
Authorities in Bahia state have so far confirmed 35 of the reported cases of Zika-related microcephaly, and discarded 27. The state still has 533 other suspected cases of Zika-related microcephaly that it will investigate, officials said.
Although some of the suspected cases of Zika-related microcephaly have been discounted, scientists and health officials are hardly breathing easy.
There is some preliminary evidence that even babies born in Brazil with normal-size heads may have developmental defects, according to Albert Ko, an infectious disease doctor and chair of the Department of Epidemiology of Microbial Diseases at the Yale School of Public Health. Ko has been working with colleagues at maternity hospitals in Salvador, Brazil’s third-largest city and one of the places where the epidemic is most pronounced, to study what is causing the birth defects in newborns.
Ko cautioned that the evidence so far is “extremely anecdotal.” But it is worrisome, he said, because clinicians are finding neurological lesions and smaller brains even in babies who look normal.
Clinicians started identifying larger than expected numbers of fetuses with birth defects during ultrasound screenings in July, August and September, he said. Some of the babies were born with intracranial lesions that may be due to infection with Zika virus.
Researchers in Brazil are working with the Brazilian health ministry to pin down answers, he said.
Sun reported from Washington.