Zika virus infections cannot be accurately diagnosed solely on the basis of microcephaly screening, reveals a study published in the journal The Lancet . “Substantial proportion” of newborns with definite or probable Zika virus infection present head circumference in the normal range.
The study warns that focusing on microcephaly (small head) alone will lead to an underestimation of the true magnitude of the Zika epidemic. Besides head circumference, signs and symptoms of brain abnormalities should also be included in the screening criteria to detect all newborns affected by Zika virus, the study suggests.
Following the Zika outbreak in northeast Brazil, a surveillance system for microcephaly was set up and suspected cases were selected solely on the basis of small head circumferences. “The initial focus on equating congenital Zika virus infection with microcephaly should be modified,” the authors write.
“The Brazilian Ministry of Health is revising the current protocols in the light of the findings from the study and the current literature,” says Giovanny V.A. Franca, the first author from the Ministry of Health, Brazil in an email to The Hindu .
While Zika virus infection during the first trimester of pregnancy is more likely to cause microcephaly, infection during the third trimester is associated with brain abnormalities despite having normal-sized heads. During an epidemic, there are fewer chances of under-reporting of microcephaly, but babies affected late during pregnancy will be missed as they have normal head circumference, the researchers warn. Cranial growth takes place only up to 30 weeks, so newborns infected late in pregnancy will not have microcephaly but can still suffer from neurological damage.
According to the study, one in five newborns with confirmed or probably Zika virus infection had head circumference in the normal range and one third of the newborns with confirmed or probably Zika virus infection were not born to mothers who had rash during pregnancy.
“Because many definite or probable cases present normal head circumference values and their mothers do not report having a rash, screening criteria must be revised in order to detect all affected newborn babies,” the authors write.
The researchers reviewed 1,501 newborns already investigated by Brazil’s health authorities between November 2015 and February 2016. While 899 cases were found to be normal, the remaining 602 newborns either had definite or probable Zika virus infection (76 had definite infection and 526 were probable cases). The definite cases had laboratory evidence of Zika virus infection, while the probable cases did not have lab confirmation but had imaging reports.
As of June 15, 1,581 cases of confirmed microcephaly and other nervous system disorders were reported in Brazil.
