Women who are infected with the Zika virus in up to the first 12 weeks of pregnancy have at least a 14 percent risk of delivering a baby with microcephaly -- a condition associated with insufficient development of the brain -- according to estimates by a University of Tokyo team published in an online U.S. epidemiology journal on March 17.
The Zika virus is continuing to spread throughout the Central and South American region. In what is the first study on patient data from Brazil -- one of the countries affected by the spreading virus -- the team stated that "the rate of microcephaly is particularly high in Brazil's northeastern region, possibly reaching up to 50 percent."
As such, the team advised caution with respect to travel by pregnant women to the region.
The effects of the Zika virus infection in early pregnancy are believed to be significant as the link between the virus and infant microcephaly continues to be strongly called into question.
At the same time, however, the actual rate of microcephaly is not clearly known.
The University of Tokyo team, whose members include Yuichiro Miyamatsu, a specially-appointed researcher of infectious disease epidemiology, based their provisional calculations upon factors including the number of patients last year in Brazil's northeastern region who were suspected of having dengue fever -- whose symptoms are similar to the Zika virus -- as well as the total number of microcephaly cases.
If the number of patients who were confirmed of having dengue fever are subtracted from the total number of cases, and if the remaining patients are postulated to have contracted the Zika virus, the rate of microcephaly stands at 14 percent.
By using a separate study conducted in a specific part of the region and presuming that the Zika infection rate was around 30 percent, the team's calculation reached a microcephaly rate of 46.7 percent.
Meanwhile, a team including members from the Pasteur Institute in France said on March 15 that based upon data from French Polynesia in the Southern Pacific Ocean, which experienced microcephaly outbreaks in 2013-14, the estimated rate of babies born with the condition when their mothers were infected with the Zika virus in early pregnancy stood at 1 percent.
The team reported their findings in the British journal The Lancet, saying that "the risk is around 50 times higher than usual."
Miyamatsu commented with respect to the discrepancy between the two studies, "The reason for the difference in figures is likely to be the subject of forthcoming discussion."